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Prevalence of anthelmintic resistance on sheep and goat farms in the mid-Atlantic region and comparison of in vivo and in vitro detection methods
... Comparisons of these values were used to ascertain the anthelmintic resistance status of each flock. It was deemed that, for H. contortus: 1) the critical wells associated with LC 50 values corresponded to FECRT ≥ 95% and were classified as susceptible; 2) wells associated with delineating doses (LC 90 -LC 95 ) corresponded to FECRT between 80% to 94% and were classified as presenting suspected resistance; and 3) wells associated with the discriminatory dose value (LC 99 ) corresponded to FECRT ≤ 79% and were classified as resistant (adapted from Crook et al., 2016). ...
... The degree of concordance between the efficacy (i.e. the parasite was susceptible, suspected of resistance or resistant) found for each chemical group in the FECRT and the critical well obtained in the LDT (where there was 50% inhibition of larval development + 95% CI) was ascertained. Then, it was also found an association with the concentration of the drug that was in that critical well (Crook et al., 2016). The Fisher's Exact Chi-square test was used to compare the resistance status of H. contortus regarding each chemical group in each flock, and to analyze the level of agreement between the in vivo field test (FECRT) and the in vitro laboratory test (LDT), in order to validate the RESISTA-Test©. ...
... The present study indicated that a good association existed between FECRT and LDT with regard to detection of H. contortus resistant to benzimidazoles and TBZ. Similar findings were reported by Grimshaw et al. (1994) using the FECRT, egg hatch test and LDT on sheep farms in southern England, and by Crook et al. (2016) on sheep and goat farms in the Central Atlantic region of the United States. High frequency of resistance to benzimidazoles (BZs) in the state of São Paulo was previously described by Veríssimo et al. (2012). ...
This study evaluated the resistance status of Haemonchus contortus from sheep flocks in the state of São Paulo, Brazil, through comparison between the fecal egg count reduction test (FECRT) and the larval development test (LDT). For the FECRT, 35 sheep were selected in each of five flocks and divided into groups treated with: benzimidazole, levamisole, ivermectin, monepantel and control. Feces were collected for EPG and fecal cultures. The LDT was performed using thiabendazole (TBZ), levamisole (LEV), ivermectin aglycone (IVM-A) and Zolvix (ZLV). Resistance to all drugs was detected using FECRT in 100% of the flocks, except in relation to ZLV (40% resistant and 20% suspected of resistance). LDT indicated resistance to TBZ and IVM-A in all flocks, to LEV in 80% of flocks and to ZLV in 10%. Total agreement was obtained between the two tests for TBZ and IVM (k = 1.0), while for LEV (k = 0.8) and ZLV (k = 0.9), substantial and almost perfect agreement were obtained, respectively. The concordance between the tests was significant, thus showing that it is possible to use the outcome of the LDT to predict the FECRT, and hence validating the former as a fast diagnostic test for use by sheep farmers in Brazil.
... Therefore, the most efficient in vitro test is the larval development test (LDT) which currently exists in several modifications allowing detection of AR to all three anthelmintic classes [7][8][9][10]. The LDT offers an alternative to the laborious in vivo FECRT and allows investigation of AR to all anthelmintic classes in a single test regardless of the herd size [11]. Moreover, the LDT is the only in vitro AR diagnostic test that has been commercialized and registered on the market as Dren-chRite® [12]. ...
... Very close are results of a recent Slovakian study [15]. Many studies have demonstrated the existence of AR to the main anthelmintic classes in goat herds outside of Europe, namely in the United States [11,16], Cuba [17], Kenya [18], South Africa [19], Uganda [20], Ethiopia [21], Malaysia [22,23], India [24][25][26], and Pakistan [27]. ...
... Similar surveys based on in vitro tests have so far been conducted in Europe on sheep flocks in Lithuania [9,34] and Ireland [35], and sheep and goat flocks in Slovakia [15,36]. Moreover, the LDT is a commonly applied technique in the AR prevalence studies in the United States [11,16,37,38], Philippines [39,40], Canada [41] and the New Zealand [42,43] in both goat and sheep flocks. The LDT allows to estimate efficacy of anthelmintics in nematode populations from small farms where performance of a FECRT for even one anthelmintic would be impractical [11,40]. ...
Background
Helminthic infections, in particular those caused by gastrointestinal nematodes (GIN), are found worldwide and are among the most economically important diseases of goats. Anthelmintic resistance (AR) in GIN of goats is currently present worldwide, and single- or multidrug resistant species are widespread. The aim of this study was to determine the prevalence of AR to benzimidazoles (BZ), macrocyclic lactones (ML) and imidazothiazoles represented by levamisole (LEV) in the Polish goat herds by using an in vitro larval development test, which is useful especially in large-scale epidemiological surveys.
Results
This cross-sectional study was conducted from September 2018 to June 2019 and enrolled 42 dairy goat herds scattered over the entire country. The most commonly used anthelmintic class in goat herds in Poland were BZ (92%), followed by ML (85%) and LEV (13%). BZ-resistant GIN populations were found in 37 herds (88%, CI 95%: 75 to 95%), ML-resistant GIN populations in 40 herds (95%, CI 95, 84 to 99%), and LEV-resistant GIN populations in 5 herds (12%, CI 95%: 5 to 25%). Multidrug resistance involving all three anthelmintic classes was found in 5 herds (12%, CI 95, 5 to 25%). Based on the morphological features of stage 3 larvae the main resistant GIN turned out to be Haemonchus contortus and Trichostrongylus spp. The use of BZ and frequency of anthelmintic treatments were significantly related to the presence of AR to BZ in Polish goat herds.
Conclusions
This cross-sectional study demonstrates the existence of AR to BZ, ML and LEV on Polish goat farms. Resistance to BZ and ML is widespread, while AR to LEV is currently at a low level. A considerable proportion of herds harbours multidrug resistant GIN, which requires further consideration. An effective anthelmintic treatment strategy, reasonable preventive measures and better understanding of the resistance-related management practices by farmers and veterinarians may delay further development of AR.
... are of the greatest concern (Howell et al., 2008). Estimates of anthelmintic resistance in common sheep GIN have been conducted in the Eastern U.S. (Howell et al., 2008;Crook et al., 2016), Eastern Canada (Falzon et al., 2013 a & b), and South Central U.S. (Tsukahara et al., 2017), indicating regionally nuanced resistance to current anthelmintic drug classes. Regional studies estimating resistance can help guide best management practices and inform adaptive strategies to combat GIN. ...
... The Drenchrite LDA® was performed according to the manufacturer's recommendations and as previously described by this laboratory (Kaplan et al., 2007;Howell et al., 2008;Crook et al., 2016). Third-stage larvae (L 3 ) in each well were counted and identified to genus (Dinaburg, 1942;M.A.F.F., 1977). ...
... Haemonchus contortus represented ≥ 50% of larvae identified from coprocultures on 18 of 25 (72%) sheep operations sampled, similar to reported results from previous field studies in the Mid-Atlantic (79%; Crook et al. 2016) and Ontario, Canada (>80%; Falzon et al., 2013a), but less than that reported from the Southeastern U.S. (96%; Howell et al. 2008). Additionally, the proportion of operations with ≥ 50% H. contortus increased with increasing EPG class (Fig. 2). ...
The objectives of this study were to provide baseline estimates of gastrointestinal nematode (GIN) prevalence and species composition on sheep operations grazing irrigated or sub-irrigated pastures, quantify anthelmintic resistance utilizing a commercially available larval development assay (LDA), and identify management risk factors from producer responses to survey data. Sampling occurred during the summers of 2017 to 2019 on 25 sheep operations in Montana (n = 15), Wyoming (n = 9), and Utah (n = 1). Operations were selected for the study based on word-of-mouth solicitation and limited to those with a history of GIN challenges. Fecal samples collected at each operation were composited into a single sample for coproculture and LDA analysis. Overall, H. contortus was the most commonly identified GIN across operations (68.5%) followed by Tri-chostrongylus (12.4%), Oesphagostumum (8.9%), Teladorsagia (8.4%), and Cooperia (1.8%). Twelve operations were evaluated for resistance to H. contortus using the LDA for benzimidazoles, ivermectin, and moxidectin. Results indicated that resistance to H. contortus was highly prevalent with benzimidazoles (91.7%), followed by ivermectin (50%) and moxidectin (8.3%). Grazing system and prior use of the corresponding anthelmintic class did not significantly impact H. contortus susceptibility to iver-mectin. Questionnaire responses indicated that 56% of producers attributing production losses to GIN in 0 to 10% of their flock but only 25% utilized targeted treatment methods to guide anthelmintic administration. Results from the present study indicate that anthelmintic resistance to multiple drug classes is a concern in Intermountain West flocks that routinely utilize irrigated pastures as a forage base.
... In the southern United States where small ruminant production is considerably challenged by internal parasitism, predominant organisms are Haemonchus contortus (Miller and Craig, 1996;Zajac and Gipson, 2000;Crook et al., 2016) and Trichostrongylus colubriformis (Terrill et al., 2001;Howell et al., 2008), particularly the former. Anthelmintic resistance of these genera was first reported in Texas (Miller and Craig, 1996) and later in the southeastern United States (Zajac and Gipson, 2000;Terrill et al., 2001). ...
... Anthelmintic resistance of these genera was first reported in Texas (Miller and Craig, 1996) and later in the southeastern United States (Zajac and Gipson, 2000;Terrill et al., 2001). Information from these regions has been updated (Howell et al., 2008;Goolsby et al., 2017), and resistance in the mid-Atlantic region has been evaluated (Crook et al., 2016). There are few reports of anthelmintic resistance in the southcentral United States other than a field day proceedings report of Miller and Gipson (2003) conducted on Oklahoma farms quite some time ago. ...
... This was true even for farms not reporting any previous use of EPM or MOX (i.e., S1 and S3 farms). Hence, efficacy of macrocyclic lactone products in the southcentral United States may be low, which agrees with other reports for the southeastern (Miller and Craig, 1996;Zajac and Gipson, 2000;Howell et al., 2008;Goolsby et al., 2017) and mid-Atlantic regions of the United States (Crook et al., 2016). In this regard, Howell et al. (2008) indicated that a general lack of biosecurity, frequent farm introduction of new animals, insufficient quarantine procedures, and a failure to treat arrivals with effective anthelmintics all contribute to increasing anthelmintic resistance. ...
An in vivo fecal egg count reduction (FECR) test was conducted on 5 farms in the southcentral United States participating in an animal resistance selection project to assess internal parasite resistance to anthelmintics. Seventy-six Kiko does on farm G1, 54 Spanish does (G2), 37 Katahdin sheep (S1), 61 Dorper ewes (S2), and 80 St. Croix sheep (S3) were randomly allocated within farm to control and 3 classes of anthelmintics. After determining initial fecal egg count, recommended doses of anthelmintics were given and fecal egg count was assessed 7 to 8 d later. Resistance to eprinomectin was detected on all farms, with FECR <63%. There was no levamisole resistance on sheep farms (FECR >95%). There was resistance to albendazole on 4 farms (FECR <95%). An egg hatch test was conducted to evaluate resistance to albendazole using composite fecal samples from untreated animals of G1, S1, S2, and S3 farms as well as control eggs from susceptible larvae. Final concentrations of albendazole were 0.00005, 0.0005, 0.005, 0.05, 0.5, and 2.0 μg/mL. After 48 h of incubation at 25°C, numbers of unhatched eggs and larvae per well were counted. The hatched percentage of susceptible larvae was 96% in the control wells. Drug concentration affected (P < 0.01) the percentage of unhatched eggs for S2 and S3, whereas values were similar (P > 0.10) for G1 and S1. In conclusion, resistance to common anthelmintics varied considerably among farms and products, suggesting a need for such testing rather than general treatment recommendations.
... Doses in prescriptions of available anthelmintics for goats in Thailand are based on doses recommended for sheep, and these doses are lower than suitable doses for goats. Metabolism of anthelmintics in goats is faster than in sheep, and 2 times the recommended dose for sheep should be used in goats [26]. Regarding the double dose recommendation, 36.0% of farmers in this study were considered overdosing their goats with ivermectin. ...
... All farmers in the present study were informed of AR status in their herds by the research team, as [26]. Levamisole was suggested for anthelmintic treatment in this area. ...
Background and aim:
Promotions of goat farming by both public and private sectors encouraged considerable goat raising in central Thailand. Gastrointestinal nematodes (GIN) infection is a major health and economic problem; however, evidence of resistance to broad-spectrum anthelmintics is frequently reported. Investigation of anthelmintic resistance (AR) status and identification of factors related to the development of AR is important components for sustainable GIN control. However, no information is available on this topic in the study area. The present study aimed to gather information on GIN control practices and to evaluate the effectiveness of albendazole, ivermectin, and levamisole for treating GIN infestation in goat herds in Sing Buri Province.
Materials and methods:
Twenty-nine herds were randomly selected. Information on management practices was collected by face-to-face interview using a structured questionnaire. Three field experiments for routinely used anthelmintics, including albendazole, ivermectin, and levamisole were conducted from June 2019 to November 2019. Fecal samples were collected pre- and post-treatment and examined for fecal egg count reduction to determine the status of anthelmintic resistance of goat GIN.
Results:
Several improper practices were identified that lead to AR, especially chronic use of albendazole and ivermectin. All herds were considered resistant to albendazole and ivermectin, and levamisole resistant nematodes were detected in two herds. AR was strongly linked with the continuous use of anthelmintics.
Conclusion:
Levamisole, which was still effective in the province, should be used with caution to minimize the selection of resistant strains. Farmers should be provided with updated information for sustainable parasite control. Further, the efficacy of anthelmintics should be routinely monitored.
... Therefore, interest was directed towards in vitro tests for detecting AR. These provide comparable and reliable results and can detect low proportions of resistant worms in a population, with the sensitivity that has potential in determining resistance with field tests [34][35][36][37]. ...
... There are several studies indicating that FECRT could un-derestimate low levels of BZ resistance. Crook et al. [36] showed the disagreement between the results of FECRT and LDT on two goat farms, where susceptibility to albendazole were indicated by FECRT and LDT indicated resistance to BZs. In the survey of Diez-Banos et al. [56] performed on sheep flocks, the BZs resistance using FECRT was found in 18% (13) of flocks, whereas 29% (21) of flocks were found to be resistant to BZs when EHT was used. ...
Currently, there are three classes of anthelmintics most commonly used in small ruminants: the benzimidazoles (BZs), macrocyclic lactones (MLs) and cholinergic agonists (especially levamisole; LEV). The widespread use of those products has led to the emergence of drug-resistant parasite strains which represents a serious threat to the livestock industry. In the present study, we describe for the first time a case of resistance to anthelmintics in goats in Romania. The study was carried out in 2021 in a dairy goat herd from the Transylvania region. Two types of diagnostic methods were used to confirm anthelmintic resistance (AR). First, the faecal egg count reduction test (FECRT), an in vivo AR diagnostic method, was used to evaluate the efficacy of eprinomectin (EPM). The results of this test were analysed applying two different calculative methods that are used only in treated animals (without the control group). Furthermore, two in vitro methods were used: the egg hatch test (EHT) for the detection of resistance to BZs, and the larval development test (LDT) for detection of resistance to all three classes of anthelmintics. The results of FECRT indicate the resistance of gastrointestinal nematodes (GINs) to EPM in both calculative methods (FECR1 = −88% and FECR2 = −202%). In addition, the results obtained for ivermectin aglycone (IVM-AG) in LDT also indicate resistance to drugs from MLs group, especially avermectins. Similarly, the results of in vitro methods (EHT and LDT) indicate resistance to BZs in this herd. LEV was the only drug that stopped the development of L3 larvae 100% (LDT). H. contortus was the only nematode species found in coproculture after EPM treatment. Furthermore, H. contotus L3 larvae was the only species found in the wells with the highest concentrations of thiabendazole (TBZ) and IVM-AG in LDT. This suggests that resistance to both BZs and MLs was present for that species.
... These parasites are frequently controlled by the use of synthetic parasiticides. However, due to drug resistance of these parasites ( et 8;TARIQ, 2017), use of multiple and regular doses of anthelmintics is increasingly observed, causing negative effects on the development of natural immunity in the animals, and consequently promoting even more parasitic resistance to various chemical groups (CROOK et al., 2016;SANTOS et al., 2017). This resistance has been observed worldwide (KANETO et al., 2016;MUCHIUT et al., 2018), and the widespread use of parasiticides has resulted in the presence of medicinal residues in foodstuffs of animal origin, as well as in the environment (SMITH et al., 2013). ...
... Another important consideration that has often been observed in sheep concerns the high drug resistance to synthetic anthelmintics. This problem is incre sing presents wor dwide occurrence nd h s been reported in v rious chemic princip es ( et 8;CROOK et al., 2016;MUKHERJEE et al., 2016;SANTOS et al., 2017;TSUKAHARA et al., 2017). Thus, this problem may also have influenced the results of the present study for ovine species. ...
... (Howell et al., 2008). In the mid-Atlantic region, multi-drug resistance was detected on 18% of farms, with complete drug failure on 12% of them (Crook et al., 2016), whereas in the western region of the country, anthelmintic resistance is less prevalent (Kaplan, 2020). ...
Haemonchus contortus is one of the most pathogenic nematodes affecting small ruminants globally and is responsible for large economic losses in the sheep and goat industry. Anthelmintic resistance is rampant in this parasite and thus parasite control programs must account for drug efficacy on individual farms and, sometimes, whether H. contortus is the most prevalent trichostrongylid. Historically, coproculture has been the main way to determine the prevalence of H. contortus in faecal samples due to the inability to morphologically differentiate between trichostrongylid egg types, but this process requires a skilled technician and takes multiple days to complete. Fluoresceinated peanut agglutinin (PNA) has been shown to specifically bind H. contortus and thus differentiate eggs based on whether they fluoresce, but this method has not been widely adopted. The ParasightTM System (PS) fluorescently stains helminth eggs in order to identify and quantify them, and the H. contortus PNA staining method was therefore adapted to this platform using methodology requiring only 20 min to obtain results. In this study, 74 fecal samples were collected from sheep and analyzed for PNA-stained H. contortus, using both PS and manual fluorescence microscopy. The percentage of H. contortus was determined based on standard total strongylid counts with PS or brightfield microscopy. Additionally, 15 samples were processed for coproculture with larval identification, and analyzed with both manual and automated PNA methods. All methods were compared using the coefficient of determination (R2) and the Lin’s concordance correlation coefficient (ρc). ParasightTM and manual PNA percent H. contortus results were highly correlated with R2=0.8436 and ρc=0.9100 for all 74 fecal samples. Coproculture versus PS percent H. contortus were also highly correlated with R2=0.8245 and ρc=0.8605. Overall, this system provides a rapid and convenient method for determining the percentage of H. contortus in sheep and goat fecal samples without requiring specialized training.
... [25]. When excrements of sheep and goats from 34 farms in mid-Atlantic U.S. regions were analyzed, H. contortus was the most common parasite found in feces, resistant to benzimidazoles almost in 100% of farms [26]. For these reasons, there is a great need to find and determine new active compounds which will be also effective against resistant strains of H. contortus. ...
Most drugs used in the treatment of helminthiasis in humans and animals have lost their efficacy due to the development of drug-resistance in helminths. Moreover, since anthelmintics, like many pharmaceuticals, are now recognized as hazardous contaminants of the environment, returning to medicinal plants and their products represents an environmentally friendly way to treat helminthiasis. The goal of the present study was to test the anthelminthic activity of methanol extracts of eight selected European ferns from the genera Dryopteris , Athyrium and Blechnum against the nematode Haemonchus contortus , a widespread parasite of small ruminants. Eggs and adults of H. contortus drug-susceptible strain ISE and drug-resistant strain WR were isolated from experimentally infected sheep. The efficacy of fern extracts was assayed using egg hatch test and adults viability test based on ATP-level measurement. Among the ferns tested, only Dryopteris aemula extract (0.2 mg/mL) inhibited eggs hatching by 25% in comparison to control. Athyrium distentifolium , Dryopteris aemula and Dryopteris cambrensis were effective against H. contortus adults. In concentration 0.1 mg/mL, A. distentifolium , D. aemula , D. cambrensis significantly decreased the viability of females from ISE and WR strains to 36.2%, 51.9%, 32.9% and to 35.3%, 27.0%, 23.3%, respectively in comparison to untreated controls. None of the extracts exhibited toxicity in precise cut slices from ovine liver. Polyphenol’s analysis identified quercetin, kaempferol, luteolin, 3-hydroxybenzoic acid, caffeic acid, coumaric acid and protocatechuic acid as the major components of these anthelmintically active ferns.
... In the mid-Atlantic region study performed a few years later (2007 to 2009), the prevalence of moxidectin resistance was twice as high at 47% of farms. 12 We also have collected data (unpublished) on resistance on sheep and goat farms in other areas of the US. From 2004 to 2015 we tested 29 sheep and goat farms in Michigan and the surrounding states (Wisconsin, Illinois, Indiana, Ohio). ...
Control of gastrointestinal (GIN) parasites is of primary concern in any small ruminant health management program, and is critical to profitability of the farm. For many years, GIN were controlled by the frequent use of anthelmintics, and this approach was quite effective. However, we now know that this strategy is shortsighted and unsustainable. Anthelmintic resistance is bounding out of control, and many of the drugs relied upon for decades no longer are effective on many farms. Furthermore, despite the occasional development of new anthelmintic classes, history clearly demonstrates that the development of resistance is almost certain to outpace the introduction of new drug classes. Thus, anthelmintics can no longer be viewed as inexpensive management tools, but instead must be viewed as extremely valuable and limited resources. Furthermore, parasite control must no longer be equated with a deworming program. Rather, parasite control will only be sustainable if it is approached as an integrated parasite management program, where anthelmintics are only 1 of several components. Additionally, there are new strategies for how we need to use our anthelmintics, the most important of which are that treatment is given selectively to animals based on need, and multiple anthelmintics are administered as a combination treatment.
... To control them, farmers often administer AH drugs to their animals at frequent intervals, most of the time without following good practices, such as the timing and frequency of deworming or the selection of molecules tailored to the parasite population, type of sheep/goat production system and season. This fact has led to an increase in multi-drug resistance (MDR) in populations of gastrointestinal nematodes [3]. ...
Infections caused by gastrointestinal parasites have been described worldwide as one of the most important issues impacting small ruminant production. The systematic administration of anthelmintic (AH) drugs without following good practice principles has led to an increase in an-thelmintic resistance (AR). There is scarce information regarding AH efficacy in small ruminants in Portugal. This study aimed to characterize by in vivo methods the presence and level of AR in four farms in the region of Lisbon and Tagus Valley. All four farms kept small herds in extensive management systems and used different deworming protocols. The active substances used were fen-bendazole and a combination of mebendazole plus closantel in a dosage according to the manufac-turers' instructions. On day 0 (T0), fecal samples were collected from all study animals, and animals in the treatment group (n = 40) were dewormed with the AH previously chosen by the assistant veterinarian. Animals in the control group (n = 30) did not receive any AH drug. The fecal sample collection was repeated on day 15 (T15), and the control group was treated. Egg counts were performed using the McMaster method for the eggs per gram (EPG), and AR was evaluated by the fecal egg count reduction test (FECRT) with a 95% confidence level (CL). The results from this experiment indicated that the four farms presented AR with two farms to fenbendazole (FECRT of 48% and 85%) and two farms to mebendazole plus closantel (FECRT of 66% and 79%). These results indicate that the gastrointestinal parasites of the four studied Portuguese farms are resistant to ben-zimidazoles, which suggests an increase in AR regarding nematodes in small ruminant production systems in Portugal.
... For parasite control, most farms administer anthelmintics to their animals at frequent intervals, without considering the principles of integrated and sustainable parasite management. This has led to the growth of a secondary problem caused by the development of drugresistant gastrointestinal nematode populations worldwide, especially the parasite H. contortus (Crook et al., 2016). ...
Haemonchus contortus is a highly pathogenic and prevalent helminth that causes many deaths in sheep herds. Anthelmintics are usually employed to overcome this issue; however, they do not guarantee immediate and lasting efficacy because of the occurrence of drug-resistant parasites. Among substances that are used in scientific studies for parasitic control, essential oils are known to have different pharmacological properties. However, they demonstrate instability owing to several factors, and therefore, nanoemulsification is considered an alternative to control the instability and degradability of these compounds. The objective of this study was to evaluate the cytotoxicity of nanoemulsions containing essential oil of Eucalyptus globulus against the blood of healthy sheep and to verify their activity against the parasite H. contortus in sheep. The results presented adequate nanotechnological characteristics (diameter 72 nm, PDI 0.2, zeta −11 mV, and acidic pH) and adequate morphology. Further, the corona effect and cytotoxic profiles of the free oil and nanoemulsion against blood cells from healthy sheep were evaluated. The tests results did not present a toxicity profile. For evaluating efficacy, we observed an important anthelmintic action of the nanoemulsion containing oil in comparison to the free oil; the results demonstrate a potential role of the nanoemulsion in the inhibition of egg hatchability and the development of larvae L1 to L3 (infective stage). Based on these results, we developed an important and potential anthelmintic alternative for the control of the parasite H. contortus.
... Resistance to four of the major classes of anthelmintic (benzimidazoles, imidazothiazoles such as levamisole (LEV), macrocyclic lactones and amino-acetonitrile derivatives) has been reported (Sangster and Gill, 1999;Wolstenholme et al., 2004;Gilleard, 2013;Van den Brom et al., 2015) and the prevalence of multidrug resistance is increasing in many areas (Kaplan, 2004;Geurden et al., 2014;Kotze and Prichard, 2016). Resistance to LEV is less common than to other broad-spectrum anthelmintics (Cernanská et al., 2006;Van den Brom et al., 2013;Crook et al., 2016;Rose-Vineer et al., 2020) and, as such, it remains an important control option for the livestock industry. ...
Haemonchus contortus is a haematophagous parasitic nematode that infects small ruminants and causes significant animal health concerns and economic losses within the livestock industry on a global scale. Treatment primarily depends on broad-spectrum anthelmintics, however, resistance is established or rapidly emerging against all major drug classes. Levamisole (LEV) remains an important treatment option for parasite control, as resistance to LEV is less prevalent than to members of other major classes of anthelmintics. LEV is an acetylcholine receptor (AChR) agonist that, when bound, results in paralysis of the worm. Numerous studies implicated the AChR sub-unit, ACR-8, in LEV sensitivity and in particular, the presence of a truncated acr-8 transcript or a deletion in the acr-8 locus in some resistant isolates. Recently, a single non-synonymous SNP in acr-8 conferring a serine-to-threonine substitution (S168T) was identified that was strongly associated with LEV resistance. Here, we investigate the role of genetic variation at the acr-8 locus in a controlled genetic cross between the LEV susceptible MHco3(ISE) and LEV resistant MHco18(UGA2004) isolates of H. contortus. Using single worm PCR assays, we found that the presence of S168T was strongly associated with LEV resistance in the parental isolates and F3 progeny of the genetic cross surviving LEV treatment. We developed and optimised an allele-specific PCR assay for the detection of S168T and validated the assay using laboratory isolates and field samples that were phenotyped for LEV resistance. In the LEV-resistant field population, a high proportion (>75%) of L3 encoded the S168T variant, whereas the variant was absent in the susceptible isolates studied. These data further support the potential role of acr-8 S168T in LEV resistance, with the allele-specific PCR providing an important step towards establishing a sensitive molecular diagnostic test for LEV resistance.
... Apart from benzimidazoles, there are reports of the development of multi-drug resistance in Haemonchus spp. in goats. Multidrug resistance was observed in the Atlantic region (Crook et al. 2016), France (Chartier et al. 2001;Bordes et al. 2020), Switzerland (Schnyder et al. 2005), India (Easwaran et al. 2009 Chemical means of control using anthelmintic compounds have resulted in widespread resistance among parasites. Hence, other non-chemical methods have been suggested to control haemonchosis in small ruminants. ...
Haemonchosis is one of the major parasitic infestations in small ruminants and one of the significant causes for loss of production, morbidity and mortality in young sheep and goats. Conventional strategies for the control of haemonchosis involve breaking the life cycle of the worm using anthelmintic drugs, pasture management and animal management. However, indiscriminate and wide use of anthelmintic compounds may attribute to the development of resistance in the parasites. Therefore, a sustainable strategy needs to be implemented to effectively control haemonchosis in goats. One of the ways to achieve this is to breed animals for disease resistance. There are various genetic loci identified in goats that can be uzed as genetic markers to select resistant animals. However, their direct utilization in developing nations and field situations may be difficult due to the higher cost of gene based selection and multifactorial nature of the trait. Hence, breeding for nematode resistance in goats will require a more integrated approach using indicator traits to identify resistant breeds/lines/ animals and then adopting gene-based selection for organized farms.
... In Uganda, 58%, 52%, and 38% AR prevalence in goat farms were detected for ivermectin, levamisole, and albendazole, respectively [27]. According to study by Crook et al. [28], H. contortus, Trichostrongylus colubriformis, and Teladorsagia cirumcincta developed resistance against levamisole and oxfendazole. Multidrug resistance was also recorded by H. contortus in sheep and goat. ...
Gastrointestinal parasites and their anthelmintic resistance are major constraints to goat production in Ethiopia. Experimental investigation by faecal egg count reduction test (FECRT) and larval cultures were used to assess the occurrence of anthelmintic resistance in naturally infected goats with gastrointestinal nematodes (GIN) in Haramaya, Ethiopia. One hundred goats with a minimum of 150 eggs per gram (EPG) count were selected and randomly divided into five groups, 20 goats in each group, four treated and one untreated group. The result of the faecal egg count reduction test percentage (FECRT%) and the lower 95% confidence limit showed the presence of anthelmintic resistance for all tested drugs except tetramisole. FECRT% and lower 95% confidence limit were 69.9% and 36.9 for albendazole, 84.3% and 66.1 for tetraclozan, 95.7% and 87.4 for tetramisole, and 71.1% and 38.2 for ivermectin, respectively. Trichostrongylus, Teladorsagia, and Haemonchus showed anthelmintic resistance for tested drugs. Coproculture from different treatment groups revealed Trichostrongylus (69.2% in ivermectin and 59.6% in albendazole) were the predominant nematode followed by Teladorsagia (21.9% in albendazole and 14.7% in ivermectin). In tetraclozan treatment group, Trichostrongylus (42%) and Teladorsagia (41.3%) were comparable, followed by Haemonchus (13%). In group treated with tetramisole, Teladorsagia (54.3%) were the most frequently detected nematode followed by Trichostrongylus (25.7%) and Haemonchus (11.4%). Therefore, this study demonstrated the presence of multidrug resistant nematodes that may limit the productivity of goats. Moreover, further studies covering wider areas of Ethiopia and mechanisms of nematode resistance need to be studied in the future.
... The incidence of helminthiasis in farm animals increases the cost of treatment, decreases production, and in some instances results in death (Miller et al. 2011;Maestrini et al. 2020). Studies by the US Department of Agriculture (USDA) demonstrated that 62% of 5174 sheep producers surveyed in the USA identified stomach/intestinal worms as a major concern (USDA 1996; Crook et al. 2016;Isaac et al. 2017a). Helminths affecting ruminants belong to three classes: Trematoda (Flukes) of which the genera Fasciola and Paramphistomum are the most important, Nematoda (Roundworms) of which the Trichostrongyles, especially the genus Haemonchus is the most important and Cestoda (Tapeworms) of which the genus Monieza is the most important (Maestrini et al. 2020). ...
Haemonchosis is a gastrointestinal parasitic disease of economic importance in ruminants especially sheep and goats. In view of the rising costs of conventional veterinary anthelmintics and the development of resistance by Haemonchus contortus, there is a need to develop alternative ethnoveterinary therapies for the treatment and management of Haemonchosis. This study investigated the anthelmintic activity of Dennettia tripetala G. Baker (Annonaceae) fruits against Haemonchus contortus in red Sokoto goats. The maximum tolerated dose was determined in adult albino rats administered, 3000, 4000, and 5000 mg/kg body weight of the crude methanol extract (CME) fraction, and observed over a period of 48 h for signs of toxicity and mortality. The in vivo anthelmintic activity was evaluated using 20 kids infected with H. contortus and randomly allocated into 5 groups (1, 2, 3, 4, and 5). Kids in groups 1, 2, and 3 were treated with CME at doses of 1250, 2500, and 5000 mg/kg respectively for 3 consecutive days per os. Groups 4 and 5 were treated with albendazole (7.5 mg/kg) once and distilled water (5 ml) respectively and served as treated and untreated controls. Blood samples were collected for haematology. The maximum tolerated dose of the CME of D. tripetala did not produce observable signs of toxicity or death in all the rats given up to 5000 mg/kg. There was significant (P < 0.05) reduction in faecal egg count by CME at doses of 1250 mg/kg (91.6%), 2500 mg/kg (98.5%), and 5000 mg/kg (100%) at day 14 post-treatment. The total plasma protein (TPP) and FAMACHA© scoring values were significantly improved (P < 0.05) in the treated groups. These results indicate that methanol extract and fractions of D. tripetala fruits possess beneficial anthelmintic activity against H. contortus and may be a suitable alternative anthelmintic candidate for the control of haemonchosis in goats.
... This treatment strategy causes selection for resistance over a short period of time , and resistant populations of parasites were found three years after the introduction of BZ compounds (Theodorides et al., 1970). Resistant populations have been selected in disparate sites throughout the world and are now extremely common so that nearly all surveyed parasitic nematode populations have BZ resistance (Howell et al., 2008;Crook et al., 2016). ...
Infections by parasitic nematodes cause large health and economic burdens worldwide. We use anthelmintic drugs to reduce these infections. However, resistance to anthelmintic drugs is extremely common and increasing worldwide. It is essential to understand the mechanisms of resistance to slow its spread. Recently, four new parasitic nematode beta-tubulin alleles have been identified in benzimidazole (BZ) resistant parasite populations: E198I, E198K, E198T, and E198stop. These alleles have not been tested for the ability to confer resistance or for any effects that they might have on organismal fitness. We introduced these four new alleles into the sensitive C. elegans laboratory-adapted N2 strain and exposed these genome-edited strains to both albendazole and fenbendazole. We found that all four alleles conferred resistance to both BZ drugs. Additionally, we tested for fitness consequences in both control and albendazole conditions over seven generations in competitive fitness assays. We found that none of the edited alleles had deleterious effects on fitness in control conditions and that all four alleles conferred strong and equivalent fitness benefits in BZ drug conditions. Because it is unknown if previously validated alleles confer a dominant or recessive BZ resistance phenotype, we tested the phenotypes caused by five of these alleles and found that none of them conferred a dominant BZ resistance phenotype. Accurate measurements of resistance, fitness effects, and dominance caused by the resistance alleles allow for the generation of better models of population dynamics and facilitate control practices that maximize the efficacy of this critical anthelmintic drug class.
... It is highly prevalent and pathogenic due to its hematophagous habit, causing gastroenteritis, anemia, weight loss, and even the death of susceptible animals (Burgunder et al., 2018;Torres-Acosta et al., 2012). It therefore causes economic losses to production systems that are exacerbated by the cost of the chemical products used for its control which, at the same time, often have low efficiency due to the increasing resistance of GIN to most anthelmintics (Callanan et al., 2018;Crook et al., 2016;Doyle et al., 2018). Several alternatives can be combined to compensate for the low efficiency of chemical products, including those that function by delaying or reducing the effects of anthelmintic resistance and improving the health conditions of animals (Arece-García et al., 2016;Campbell et al., 2017;Westers et al., 2017). ...
Nutritional aspects modulate the parasitological and immune response in infected sheep. The aim of the present study was to evaluate the parasitological and humoral immune response of Pelibuey sheep experimentally infected with Haemonchus contortus that were fed diets with two different energy (n = 12) and protein (n = 12) levels. Twenty-four Pelibuey lambs infected with H. contortus were evaluated over 12 weeks. An additional six animals were considered as a control group. Fecal egg count (FEC) was determined, in addition to packed cell volume (PCV), total plasma protein (TPP), and immunoglobulin levels (IgA, IgG, and IgM) by indirect enzyme-linked immunosorbent assay (iELISA). Data were analyzed by repeated measures over time. The lambs that received a high-energy (HighE) diet had the lowest FEC (P < 0.01) regardless of whether they received a high (HighP) or low (LowP) level of protein. The effect of energy level was also observed over time: FEC values decreased and PCV and TPP values increased. Higher immunoglobulin levels were obtained for females (P < 0.05) than males yet, overall, the energy and protein levels of the diets did not affect the response of the immunoglobulins. Over time, however, an increase in IgG and IgM was observed, whereas the IgA level remained basal.
... -Baños et al. (2008) detected BZ resistance in 18% of sheep flocks using FECRT but in 29% of the flocks using EHT.Martinez-Valladares et al. (2013) found a prevalence of 35.30% against BZ using the EC 50 criterion in EHT, which was higher than values obtained by FECRT (13.60%).Crook et al. (2016) described the discrepancy between the in vivo FECRT and the in vitro LDT on two goat farms, where LDT indicated BZ resistance but FECRT indicated susceptibility to ALB. The sensitivity of FECRT decreases with mixed infections under field conditions(McKenna 1996(McKenna , 1997a, and species diversity has a significant impact on the diagn ...
The objective of this study was to compare the results of an in vitro egg hatch test (EHT), micro-agar larval development test (MALDT) and in vivo faecal egg count reduction test (FECRT) between worm strains obtained from goats and sheep identically infected with the gastrointestinal parasitic nematode Haemonchus contortus. Results from the in vivo and in vitro tests were compared with benzimidazole (BZ)-resistance-associated β-tubulin allele frequencies determined using Pyrosequencing™. BZ resistance was not detected by the in vivo FECRT, where reductions of > 99% for both the resistant and the susceptible H. contortus strains were detected in both species. Discriminating doses in EHT and MALDT for the resistant strain indicated a low level (approx. 25%) of resistant individuals. Genotyping indicated that the susceptible strain had 10% BZ-resistant β-tubulin codon 200 alleles and the resistant strain had 26% respective resistant alleles. The in vitro tests and allele-frequency distribution suggested low levels of resistance in both strains; however, the FECRT did not support the evidence of resistant individuals of either strain in either species, suggesting a potential underestimation of low-level resistance in sheep and goats when employing this test.
... Furthermore, the results of Várady et al. [22] also suggest that LDT provides a more accurate quantitative estimate of the level of benzimidazole resistance compared to EHT. In the some cases using the in vitro methods for the detection of AR could be more suitable and sensitive, especially in herds where the resistant alleles are present in the proportion of GIN population [24][25][26]. ...
Background:
Prophylactic anthelmintic treatment with one of three basic classes of anthelmintics (benzimidazoles, macrocyclic lactones and imidazothiazoles) is still the mainstay of control of gastrointestinal nematode infections in small ruminants worldwide. As a consequence, anthelmintic resistance is a serious threat to small ruminant health and production. While the resistance to one class of anthelmintics has already been reported in most of countries, the newly-emerging problem is the resistance to two or even all of classes referred to as multidrug resistance. This study aimed to evidence the presence of multidrug resistance of gastrointestinal nematodes in goats in Poland.
Results:
The combination of one in vivo method (fecal egg count reduction test) and two in vitro methods (egg hatch test and larval development test) performed in two goat herds in the southern Poland showed the presence of gastrointestinal nematodes resistant to fenbendazole and ivermectin in both herds. Moreover, in one herd it revealed the development of resistance to the last effective anthelmintic, levamisole, in response to one-year intensive use. Haemonchus contortus was the most prevalent gastrointestinal nematode in samples in which resistance to benzimidazoles and ivermectin was found, whereas Trichostrongylus colubriformis predominated when resistance to levamisole was observed.
Conclusion:
This study shows for the first time that multidrug resistance of gastrointestinal nematodes to three basic classes of anthelmintics is already present in goat population in Poland. Moreover, it may indicate that different species or genera of gastrointestinal nematodes are responsible for the resistance to specific anthelmintics.
... Le Tableau 2 liste les principaux helminthes pathogènes gastro-intestinaux. En Guadeloupe, terrain d'étude du projet, on rencontre une vingtaine de strongles digestifs dans les élevages dont Haemonchus Contortus, Trichostrongylus colubriformis, et Oesophagostomum columbianum Guadeloupe X X X X X X X X X X X X X X (Crook et al., 2016) USA X X X X (Zainalabidi n et al., 2015) Malaisie X (A.M.G. Belem, 2005) Afrique X X X X X X X X (Kearney et al., 2016) Australie X (Herrera-Manzanilla et al., 2017) Mexique X X X (Morgan et al., 2007) Kazakhstan X X X (Di Loria et al., 2009) Italie X X X (Cériac et al., 2017) Guadeloupe X (Matos et al., 2017) Brésil X X X (Nisbet et al., 2013) Royaume-Unie X (Piedrafita et al., 2012) Australie X X X X X X X X (Arece-García et al., 2017) Cuba X X X (Chiejina and Behnke, 2011) Afrique X X X X X (Domke et al., 2013) Norvège X X X X X X X X X (Sultan et al., 2016) Egypte X X X X (Miller et al., 2011) USA X X X ...
Les infestations par les strongles gastro-intestinaux (SGI) constituent une cause majeure de morbidité et de mortalité chez les petits ruminants élevés au pâturage et entraînent donc des pertes de production. En raison de l'émergence de la résistance aux anthelminthiques et des préoccupations des consommateurs concernant les résidus chimiques dans les produits animaux, des stratégies alternatives de contrôle sont nécessaires. L'objectif n'est plus l'éradication totale de la population parasitaire, mais plutôt un meilleur contrôle de ces populations pour atteindre un équilibre favorable à la production animale entre l'hôte et les parasites. Une stratégie prometteuse pour le contrôle des SGI est l'amélioration de la réponse de l'hôte par le statut nutritionnel des animaux. Bien que les chèvres soient plus sensibles que les moutons aux infestations par les NGI, la plupart des programmes de recherche visant à caractériser les interactions hôtes-NGI est menée chez les ovins. Contrairement à l’idée que les résultats acquis chez le mouton seraient applicables aux chèvres du fait de leur proximité, de nombreuses études soulignent des différences significatives entre ces modèles. L’objectif de ce travail de thèse était d’étudier l’impact du statut nutritionnel en termes de quantité de protéines et d’énergie et de la qualité des protéines apportée par la ration sur les réponses (production vs réponse contre le parasitisme) de caprins Créole infestés expérimentalement par Haemonchus contortus. Nous avons montré que le statut nutritionnel permettait de réduire la sévérité et la durée de l’anémie régénérative et de la thrombopénie induite par H. contortus chez le caprin Créole. La ration enrichie en protéines était associée à de la résilience vis-à-vis de l’infestation plutôt que de la résistance. Le mécanisme sous-jacent serait lié à une augmentation de la capacité régénérative de la moelle osseuse. Par contre, une augmentation de la part de protéines by-pass dans la ration était associée à de la résistance. Une augmentation de la réponse humorale IgA dirigée contre les larves L3 et les produits d’excrétions sécrétés par les parasites adultes était associée à cette résistance. Nous avons aussi cherché à valider l’hypothèse d’une partition différenciée des flux d’acides aminés avec le stress provoqué par H. contortus. Nous n’avons pas mis en évidence de différences de synthèses protéiques entre tissus et pour un même tissu entre animaux infestés et non infestés. En résumé, les travaux conduits dans cette thèse ont montré qu’il existe un équilibre entre la quantité et la qualité des protéines alimentaires de la ration qui permet d’améliorer la réponse des caprins Créole contre H. contortus ainsi que leurs performances de production.
... In recent years, multiple drug resistance to old anthelmintic groups has been reported in many parts of the world (Nabukenya et al., 2014;Keegan et al., 2015;Crook et al., 2016;Herrera-Manzanilla et al., 2017). Additionally, treatment failures have been reported for new broad spectrum anthelmintics in sheep (George et al., 2012;Sager et al., 2012) and ...
Gastrointestinal nematode infection is one of the major diseases affecting sheep and goats but most of the studies have focused on sheep. As a highly productive meat breed of goats, it is important to study the response of Boer breed to gastrointestinal nematode infection. The aim of this study was to investigate the interaction between Boer goats and their gastrointestinal nematodes by evaluating the phenotypic (faecal egg counts (FEC), IgA, packed cell volume (PCV), peripheral eosinophil counts and bodyweight) and parasitological (nematode number, length and index) variables following natural and deliberate co-infections that were dominated by Teladorsagia circumcincta and Haemonchus contortus, respectively.
This study also aimed to estimate the repeatability, which provides an upper limit on heritability, and heritability of phenotypic variables among Boer goats, in particular the FEC as this is an important marker of resistance to gastrointestinal nematode infection. The study on natural infection was conducted in a farm in England with a semi-intensive grazing system whereas a deliberate infection study was conducted in a farm in Malaysia with an intensive management system.
The FEC was confirmed to follow a zero-inflated Poisson distribution after comparing the observed and predicted zeroes in a Poisson regression. Mixed model repeated measures analysis that was conducted in a Bayesian framework was then used to analyse the phenotypic data. The findings from the studies of the phenotypic variables showed that the repeatability was moderate for FEC and PCV but relatively high for IgA activity and peripheral eosinophil counts and decreased significantly as the interval between sampling increased. The repeated measures models showed that FEC variation among Boer goats was affected by eosinophilia through time with the presence of an interaction with IgA responses, but that FEC was not heritable among Boer goats.
The bodyweight of Boer goats was shown to be highly heritable despite them being infected with gastrointestinal nematodes. Additionally, the unaffected PCV levels and the increase in bodyweight over the course of infection suggest that Boer goats may be relatively resilient to gastrointestinal nematode infection.
Multiple linear regression analyses of the mean phenotypic variables and the parasitological variables measured at necropsy suggested that H. contortus and Trichostrongylus colubriformis affected each other during co-infection. Shorter T. colubriformis was associated with greater H. contortus index and number whereas longer T. colubriformis was associated with a reduction in H. contortus number. Additionally, increased in IgA activity was associated with increased H. contortus length but a reduction in T. colubriformis index during co-infection.
Together the findings show that eosinophils and IgA do play a role in the response of goats to gastrointestinal nematode infection, but the effects are less pronounced than in sheep. Moreover, the finding of a very low heritability of FEC is in contrast to findings in sheep. Most of the findings also suggest that the Boer breed is relatively resilient to infection but further work is needed to confirm whether these finding might be due to low infection doses.
In conclusion, this study has expanded knowledge of the host-parasite relationship in goats as well as demonstrating interspecific nematode interactions between H. contortus and T. colubriformis, which commonly co-infect goats under natural conditions. However, future studies that overcome the limitations in the present study are needed to confirm the resistance status of Boer goats against these nematode species.
... In Uganda, 58%, 52%, and 38% AR prevalence in goat farms were detected for ivermectin, levamisole, and albendazole, respectively [27]. According to study by Crook et al. [28], H. contortus, Trichostrongylus colubriformis, and Teladorsagia cirumcincta developed resistance against levamisole and oxfendazole. Multidrug resistance was also recorded by H. contortus in sheep and goat. ...
Background: The occurrence of anthelmintic resistance to commonly used drugs is becoming worldwide constrain in livestock production. Considering the narrow range of available drugs and slow rate of new drug development, anthelmintic resistance presents an alarming global threat demanding vigilant monitoring and management. It is likely that anthelmintic resistance of gastrointestinal goats present in Ethiopia, but little information regarding the prevalence and species of nematode resistance to drugs is available. Current study done with objective to assess anthelmintic resistance of gastrointestinal nematodes of goats to commonly used anthelmintic drugs.
Results: The result of the FECRT % and lower 95% confidence limit reported the presence of anthelmintic resistance for tested drugs; albendazole (41.5%, 36.9), tetraclozan (69.5%, 66.1), tetramisole (91.1%, 87.4) and ivermectin (43%, 38.2) respectively. Trichostrongylus spp, Teladorsagia spp and Haemonchus spp showed anthelmintic resistance for all tested drugs. Coproculture from different treated group revealed of Trichostrongylus spp (69.2% in ivermectin and 59.6% in albendazole) was the predominant nematode followed by Teladorsagia spp (21.9% in albendazole and 14.7% in ivermectin). In tetraclozan treatment group, Trichostrongylus spp (42%) and Teladorsagia spp (41.3%) were comparable, followed by Haemonchus spp (13%). In group treated with tetramisole, Teladorsagia spp (54.3%) was the major nematode detected followed by Trichostrongylus spp (25.7%) and Haemonchus spp (11.4%).
Conclusions: The study demonstrated the presence of multi-drug resistant nematodes mainly Trichostrongylus spp, Teladorsagia spp and Haemonchus spp. Control strategies including management practices of pasture rotation, supplementary feeding and encouraging traditional nematode control methods. Further studies covering wider areas of Ethiopia and mechanism of nematode resistance need to be studied in future.
... The excessive use of synthetic nematocidal generates a great monetary cost worldwide. On the other hand, H. contortus has produced an important drug resistance problem mainly in goats and sheep (Kaplan and Vidyashankar, 2012;Crook et al., 2016;Learmount et al., 2016). Additionally, the health and ecological risk produced by remnants of synthetic nematocides had increased the necessity to evaluate other alternative methods for control of helminthiasis (Waller, 1997, Waller andThamsborg, 2004). ...
... The excessive use of synthetic nematocidal generates a great monetary cost worldwide. On the other hand, H. contortus has produced an important drug resistance problem mainly in goats and sheep (Kaplan and Vidyashankar, 2012;Crook et al., 2016;Learmount et al., 2016). Additionally, the health and ecological risk produced by remnants of synthetic nematocides had increased the necessity to evaluate other alternative methods for control of helminthiasis (Waller, 1997, Waller andThamsborg, 2004). ...
The aim of this study was to evaluate the in vitro lethal effect of a hydroalcoholic extract (HAE) from Acacia cochliacantha leaf against three gastrointestinal nematodes species (Haemonchus contortus, H. placei and Cooperia punctata) of domestic ruminants. The HAE was assessed using five concentrations: 100, 125, 175, 150 and 200 mg/ml; 0.5% Ivermectin was used as a positive control and distilled water, as negative control. The data were normalized using the square root and analysed with a completely randomized design through ANOVA analysis using the general lineal model (GLM) of the SAS program. The HAE tannin content was determined through spectrophotometry (UV-visible) and the other major phenols, were identified by chromatographic processes. The results showed an in vitro larvicidal activity of the HAE against the three assessed nematode species with all assessed concentrations. A clear HAE increased concentration dependence effect was observed. The highest activity of the HAE was obtained at the highest concentration (close to 100%, P < 0.05). This result was similar to the one obtained with Ivermectin. On the other hand, the chemical analysis of HAE showed the presence of tannins, caffeoyls and coumaroyl derivates and quercetin as the main compounds. The results suggest that the HAE from this plant species possess in vitro anthelmintic properties. The identified compounds in this study would good candidates for further in vivo researches.
Most drugs used in the treatment of helminthiasis in humans and animals have lost their efficacy due to the development of drug-resistance in helminths. Moreover, since anthelmintics, like many pharmaceuticals, are now recognized as hazardous contaminants of the environment, returning to medicinal plants and their products represents an environmentally friendly way to treat helminthiasis. The goal of the present study was to test the anthelminthic activity of methanol extracts of eight selected European ferns from the genera Dryopteris , Athyrium and Blechnum against the nematode Haemonchus contortus , a widespread parasite of small ruminants. Eggs and adults of H. contortus drug-susceptible strain ISE and drug-resistant strain WR were isolated from experimentally infected sheep. The efficacy of fern extracts was assayed using egg hatch test and adults viability test based on ATP-level measurement. Among the ferns tested, only Dryopteris aemula extract (0.2 mg/ml) inhibited eggs hatching by 25% in comparison to control. Athyrium distentifolium, Dryopteris aemula and Dryopteris cambrensis were effective against H. contortus adults. In concentration 0.1 mg/ml, A. distentifolium, D. aemula , D. cambrensis significantly decreased the viability of females from ISE and WR strains to 36.2%, 51.9%, 32.9% and to 35.3%, 27.0%, 23.6, respectively in comparison to untreated controls. None of the extracts exhibited toxicity in precise cut slices from ovine liver. Polyphenol’s analysis identified quercetin, kaempferol, luteolin, 3-hydroxybenzoic acid, caffeic acid, coumaric acid and protocatechuic acid as the major components of these anthelmintically active ferns.
Anthelmintic efficacy was evaluated among sheep that had become naturally infected with gastrointestinal nematodes in 17 flocks located in the semiarid region of Minas Gerais, Brazil. Feces were collected individually from 1021 hairy sheep to determine the number of eggs per gram of feces (EPG) and for coprocultures to identify nematode genera the nematodes. Only the animals that presented EPG counts greater than or equal to 200 were included in the study (totaling 381 sheep). The animals were divided into three treatment groups: albendazole, ivermectin and levamisole. Fourteen days after the administration of anthelmintics, fecal samples were taken from all animals. In each flock, the pre-treatment and post-treatment arithmetic mean EPG were used to calculate the efficacy (FECR) for each of the treatment groups and the lower 95% confidence limit. Data were analyzed with the "eggCounts 2.3" package in RStudio, using a Bayesian model for paired design. The anthelmintics were classified as being efficacious (when the FECR was both equal to or above 95% and the lower 95% confidence limit was equal to or above 90%) or as encountering anthelmintic resistance (when the FECR was below 95% and the lower 95% confidence limit was below 90%) or inconclusive (when none of the other criteria were fulfilled). Albendazole and ivermectin were not effective in any of the flocks. Levamisole was effective against gastrointestinal nematodes in 25% of the flocks studied. Haemonchus, Trichostrongylus and Oesophagostomum genera were identified in this study in a semiarid region of Minas Gerais, Brazil. The genus Haemonchus was the most prevalent, followed by Trichostrongylus and Oesophagostomum. After anthelmintic treatment, the most prevalent genus was Haemonchus, followed by Trichostrongylus; the genus Oesophagostomum was not detected. The highest percentage of Haemonchus larvae was observed after treatment with ivermectin, followed by albendazole and levamisole. This study revealed the existence of gastrointestinal nematodes in sheep that present multiple resistance to all three main classes of anthelmintic drugs.
Albendazole (ABZ) is widely used in the treatment of animal intestinal parasitic infections. This study has established a method of ultrahigh-performance liquid chromatography coupled with fluorescence detection for the simultaneous determination of ABZ and its three metabolites (albendazole, albendazole sulfone, albendazole sulfoxide, albendazole-2-aminosulfone) in poultry (chicken, duck, and goose) eggs. Good linearity was shown under the optimized conditions with the determination coefficient (≥ 0.9994). The limits of detection (LOD) were 0.3-4.6 µg/kg, whereas the limits of quantification (LOQ) were 1.0-12.9 µg/kg. The recoveries of ABZ and its three metabolites ranged from 80.5% to 98.6%, while relative standard deviations were in the range of 1.2% to 4.8%, and all target analytes could be detected within 6 minutes. The method was demonstrated to be sensitive, selective, and quick for the detection of ABZ and its three metabolites.
OBJECTIVE
To review anthelmintic resistance globally in goats including the effect of location, mode of application and dosage on anthelmintic efficacy (assessed using Faecal Egg Count Reduction). Specifically, resistance of the three major classes of anthelmintics – Benzimidazole and Probenzimidazole (BP); Anti-cholinergics (AC); and Macrocyclic Lactone (ML) was investigated.
DESIGN/PROCEDURE
A PRISMA Framework was followed in order to conduct a thorough assessment of the literature on anthelmintic resistance in goats. A single factor ANOVA test was conducted in Microsoft Excel (2009) to test for the significance of the effect of location, mode of application and dosage on resistance. Three meta-analyses were also conducted in Microsoft Excel (2009) to quantify global resistance levels of the three major anthelmintic classes.
RESULTS
Of the 461 publications screened, 105 studies were included in the systematic review and 101 studies were included in the meta-analyses. Anthelmintic class as well as anthelmintic active principle selection in the BP and ML classes did have a significant effect on resistance (p < 0.05). Combination treatment groups had a lower amount of resistance than groups where anthelmintic classes were used alone. Mode of application of the treatment had a significant effect on resistance (p < 0.05), whilst the correlation of dosage with efficacy was low (r < 0.1). The effect of location (by continent) also had a significant influence on resistance for the AC anthelmintic class (p < 0.05). All GIN species assessed with the exception of Chabertia spp. exhibited anthelmintic resistance.
CONCLUSIONS
Anthelmintic resistance is a substantial global issue in the goat industry. More research needs to be conducted into anthelmintic resistance in regard to effective ways to use anthelmintics and minimise resistance.
Objective:
To determine whether copper oxide wire particles (COWP) administered as an oral bolus effectively decrease fecal gastrointestinal nematode (GIN) egg counts in adult alpacas.
Animals:
57 adult alpacas.
Procedures:
A double-blind clinical trial was performed during the months of April through August 2019. Adult alpacas enrolled in the trial were administered 2 g of COWP or a placebo control capsule PO on day 0 and day 45. On day 0 and at 15-day intervals, fecal samples were collected, and Modified McMaster fecal egg counts (FEC) were performed as well as physical examinations, including FAMACHA scoring and body condition scoring (BCS). Hematocrits were measured in 30-day intervals (days 0, 30, 60, and 90). Results were compared across groups.
Results:
A significant decrease in mean FEC was observed in the COWP-treated group over time, compared with the placebo group. Mean BCS, FAMACHA score, and Hct did not differ significantly between groups. No clinical evidence of copper toxicosis was observed.
Clinical relevance:
Oral administration of COWP was determined to be a safe and effective method of reducing GIN FEC in adult alpacas.
Parasitic nematodes are globally important and place a heavy disease burden on infected humans, crops and livestock, while commonly administered anthelmintics used for treatment are being rendered ineffective by increasing levels of resistance. Although the modes of action and resistance mechanisms caused by detoxification and target site insensitivity for these compounds is well documented, the mechanisms for uptake, which can also cause resistance, are still poorly defined. It has recently been shown in the model nematode Caenorhabditis elegans that the avermectins or macrocyclic lactones such as ivermectin and moxidectin gain entry though the sensory cilia of the amphid neurons. This study interrogated the molecular mechanisms involved in the uptake of avermectins using a combination of forward genetics and targeted resistance screening approaches along with visualising a BODIPY labelled ivermectin analog and confirmed the importance of intraflagellar transport in this process. This approach also identified the protein trafficking pathways used by the downstream effectors and the components of the ciliary basal body that are required for effector entry into these non-motile structures. Mutations in many of the genes under investigation also resulted in resistance to the unrelated anthelmintic drugs albendazole and levamisole, giving insights into the potential mechanisms of multidrug resistance observed in field isolates of the parasitic nematodes that are a scourge of ruminant livestock. In total 50 novel C. elegans anthelmintic survival associated genes were identified in this study, three of which ( daf-6 , rab-35 and inx-19 ) are associated with broad spectrum cross resistance. When combined with previously known resistance genes, there are now 53 resistance associated genes which are directly involved in amphid, cilia and IFT function.
Author Summary
Nematodes represent significant pathogens of man and domestic animals and control relies heavily on limited classes of Anthelminitic drugs. Single and multi-drug resistance is a growing problem however mechanisms of anthelmintic drug resistance and drug uptake by nematodes remain to be clearly elucidated. In Caenorhabditis elegans there has been an association between amphid and dye filling defects with resistance to avermectins however the effector and causal mechanisms remain elusive. This study uses a combination of fluorescently labelled anthelmintics and anthelmintic resistance screens to probe the uptake mechanisms for these drugs. The role of the sensory amphids in the uptake of avermectins was confirmed. The avermectins enter the distal segment of the cilia using an effector which is delivered by the UNC-119 and UNC-33/UNC-44 transport systems to the base of the cilia, followed by distal appendage dependent entry and transport along the cilia by the intraflagellar transport pathway. Of the genes investigated, three ( daf-6 , rab-35 and inx-19 ) were linked to cross resistance against all the anthelmintics tested (Ivermectin, Moxidectin, Albendazole and Levamisole). This study gives further insight into how important classes of anthelmintics enter nematodes and highlights the potential for this process to give rise to anthelmintic resistance.
Helminthosis is one of the greatest causes of parasitic disease and loss in animal productivity. As such, the control of helminth parasites is of critical importance. This study was aimed to investigate the in vitro anthelmintic activity of Dennettia tripetala G. Baker (Annonaceae) fruits against Haemonchus contortus. Using in vitro techniques, the anthelmintic activity of extracts and fractions of D. tripetala G. Baker (Annonaceae) was evaluated for ovicidal (Egg hatch inhibition test) and larvicidal (larval mortality test) activity. Besides, the maximum tolerated dose was determined in adult albino rats administered, 300, 400, and 500 mg/kg body weight of the CME fraction, and observed over a period of 48 h for signs of toxicity and mortality. Phytochemical screening uncovered the occurrence of flavonoids, steroids/triterpenes, cardiac glycosides, saponins, tannins, carbohydrates, and alkaloids in the crude methanol extract (CME), the ethyl acetate fraction (EAF), and butanol fraction. The maximum tolerated dose of the CME of D. tripetala did not produce observable signs of toxicity or death in all the rats given up to 500 mg/kg. The CME and EAF of D. tripetala fruits produced a significant (\(p < 0.05\)) reduction in the hatchability of H. contortus eggs in a concentration-dependent manner, while the CME at concentrations between 12.5 and 100 mg/ml completely inhibited the hatching of H. contortus eggs. Similarly, EAF at doses of 25, 50, and 100 mg/ml completely inhibited the hatching of H. contortus eggs. The CME and EAF of D. tripetala fruits produced significant (\(p < 0.05\)) larvicidal activity against L3 of H. contortus in a concentration-dependent manner while the CME at concentrations between 6.25 and 100 mg/ml caused larval mortality of H. contortus L3 larvae completely. This study suggests that methanol extract and fractions of D. tripetala fruits possess beneficial anthelmintic (ovicidal and larvicidal) activity against H. contortus, and may be a suitable alternative anthelmintic candidate for the control of nematodes.
Resistance of small ruminant gastrointestinal parasites to available classes of anthelmintic drugs is a widespread problem. As such, use of these drugs needs to be applied in a judicious manner in order to protect animal health. Herein, a case of drug-resistant gastrointestinal nematodes imported to the Cayman Islands is outlined. In order to explore the potential for similar occurrences within the region, a survey was undertaken in March 2017 to assess the importation requirements for small ruminants to English-speaking Caribbean countries. The survey showed that universal administration of anthelmintics to small ruminants is a common pre-requisite for importation to the Caribbean region, though very few countries require any proof of drug efficacy. Such requirements are discordant with current recommendations for judicious anthelmintic use in domestic animal species and promote the continued development of anthelmintic resistance. While this survey focused on small ruminants, similar policies are often in place for the importation of a variety of animal species, including cattle, horses, and companion animals. Given that anthelmintic resistance is also recognized in parasite populations that impact these species, it may be time for the international community to revisit live animal importation requirements in the age of anthelmintic resistance. Some recommendations and considerations are put forward to help preserve animal health, animal welfare, and developing animal agricultural industries.
Uncontrolled crossbreeding of indigenous tropical goats with exotic breeds to increase genetic potentials for growth and body size is a common strategy for genetic improvement. However, in most cases, goats of all genotypes are managed under similar extensive or semi-intensive conditions without corresponding improvements in feeding or health care. Fitness characters such as parasite resistance are believed to be present in indigenous goats and important under typical field conditions but potentially diluted by uncontrolled crossbreeding. This study was therefore designed to compare resistance to gastrointestinal (GI) strongyle parasites in 279 Sri Lankan Indigneous (SLI) and 243 Jamnapari crossbred (JCB) kids. Kids were 4 to 6 months old and maintained under similar management on 68 farms in the Eastern Province of Sri Lanka. Body weight (BW), packed cell volumes (PCV), and fecal egg count (FEC) were determined for each goat at the start of the study in mid-July and again 7 days later. Effects of sex and time were observed for BW, and effects of sex and sex × breed interaction were present for PCV. Kids were heavier (P < 0.05) at the second sampling time, and male kids were heavier than females (10.2 ± 0.2 versus 9.5 ± 0.2 kg). The SLI females had greater (P < 0.05) PCV (26.3 ± 0.3%) than SLI males, JCB females, and JCB males, which did not differ (P ≥ 0.54; average PCV of 24.4%). Both SLI and JCB goats had relatively low levels of GI strongyle parasitism under field conditions during the dry season in Sri Lanka, but exhibited substantial within-breed variability in FEC. The sum of FEC across the two measurement times was 1,123 ± 333 eggs per gram of feces (epg) for JCB kids and 488 ± 107 epg for SLI kids (P = 0.03), and the breed difference in FEC was larger for females than for males (P = 0.04 for breed x sex interaction). The proportion of goats with FEC > 3,000 epg was greater for JCB goats (7.2%) than for SLI goats (1.3%), and the within-farm variance in FEC with significantly greater for JCB goats. These results indicated that, when infected, JCB goats were more severely affected than SLI goats. Phenotypic resistance to GI strongyle parasites was therefore detectable under field conditions in the dry season in Sri Lanka, indicating potential to improve both parasite resistance and production potentials in tropical goats using systematic crossbreeding and selection.
Two methodologies were tested to isolate pure Trichostrongylus colubriformis strains from naturally infected sheep. Also, the in vitro susceptibility status to commercial anthelmintic (AH) drugs was determined in these strains. These methods were performed in a tropical region of Mexico where naturally infected sheep and goats host Haemonchus contortus, T. colubriformis and Oesophagostomum columbianum. For the first strain, a group of 6 naturally infected lambs from the “Paraiso” farm were treated with closantel (subcutaneous (SC), 10 mg/kg). On day 10 post-treatment, the eggs per gram (EPG) of faeces were determined with the McMaster technique. The faeces from the two lambs with the highest EPG were used for coprocultures (4 days, 28 °C). The L3 larvae were recovered and identified as T. colubriformis (69%) and O. columbianum (31%). The latter was removed by 10-day refrigeration (4–5 °C) followed by sieving (25 μm), resulting in 100% T. colubriformis (PARAISO strain). The second strain was isolated using repeated doses of levamisole (LEV, SC 7.5 mg/kg) in an 8-year-old sheep. The sheep had 1700 EPG before the LEV treatments and maintained 1300 EPG after both LEV treatments (day 10). The coproculture (4 days, 28 °C) after the second treatment contained 100% T. colubriformis (FMVZ-UADY strain). The in vitro AH susceptibility was determined using the egg hatch test for benzimidazole (BZ), and the larval migration inhibition test for ivermectin (IVM) and LEV. The PARAISO strain was BZ- and LEV-susceptible, and IVM-resistant. Meanwhile, the FMVZ-UADY strain was BZ- and IVM-susceptible, and LEV-resistant. The conditions where these two protocols could be used in other parts of the world were discussed.
Infections by parasitic nematodes inflict a huge burden on the health of humans and livestock throughout the world. Anthelmintic drugs are the first line of defense against these infections. Unfortunately, resistance to these drugs is rampant and continues to spread. To improve treatment strategies, we must understand the genetics and molecular mechanisms that underlie resistance. Studies of the fungus Aspergillus nidulans and the free-living nematode Caenorhabditis elegans discovered that a beta-tubulin gene is mutated in benzimidazole (BZ) resistant strains. In parasitic nematode populations, three beta-tubulin alleles, F167Y, E198A, and F200Y, have long been correlated with resistance. Additionally, improvements in sequencing technologies have identified new alleles - E198V, E198L, E198K, E198I, and E198Stop - also correlated with BZ resistance. However, none of these alleles have been proven to cause resistance. To empirically demonstrate this point, we independently introduced the F167Y, E198A, and F200Y alleles as well as two of the newly identified alleles, E198V and E198L, into the BZ susceptible C. elegans N2 genetic background using the CRISPR-Cas9 system. These genome-edited strains were exposed to both albendazole and fenbendazole to quantitatively measure animal responses to BZs. We used a range of concentrations for each BZ compound to define response curves and found that all five of the alleles conferred resistance to BZ compounds equal to a loss of the entire beta-tubulin gene. These results prove that the parasite beta-tubulin alleles cause resistance. The E198V allele is found at low frequencies along with the E198L allele in natural parasite populations, suggesting that it could affect fitness. We performed competitive fitness assays and demonstrated that the E198V allele reduces animal health, supporting the hypothesis that this allele might be less fit in field populations. Overall, we present a powerful platform to quantitatively assess anthelmintic resistance and effects of specific resistance alleles on organismal fitness in the presence or absence of the drug.
Infections by parasitic nematodes inflict a huge burden on the health of humans and livestock throughout the world. Anthelmintic drugs are the first line of defense against these infections. Unfortunately, resistance to these drugs is rampant and continues to spread. To improve treatment strategies, we must understand the genetics and molecular mechanisms that underlie resistance. Studies of the fungus Aspergillus nidulans and the free-living nematode Caenorhabditis elegans discovered that a beta-tubulin gene is mutated in benzimidazole (BZ) resistant strains. In parasitic nematode populations, three canonical beta-tubulin alleles, F200Y, E198A, and F167Y, have long been correlated with resistance. Additionally, improvements in sequencing technologies have identified new alleles - E198V, E198L, E198K, E198I, and E198Stop - also correlated with BZ resistance. However, none of these alleles have been proven to cause resistance. To empirically demonstrate this point, we independently introduced the three canonical alleles as well as two of the newly identified alleles, E198V and E198L, into the BZ susceptible C. elegans N2 genetic background. These genome-edited strains were exposed to both albendazole and fenbendazole to quantitatively measure animal responses to BZs. We used a range of doses for each BZ compound to define response curves and found that all five of the alleles conferred resistance to BZ compounds equal to a loss of the entire beta-tubulin gene. These results prove that the parasite beta-tubulin alleles cause resistance. The E198V allele is found at low frequencies in natural parasite populations, suggesting that it could affect fitness. We performed competitive fitness assays and demonstrated that the E198V allele reduces animal health, supporting the hypothesis that this allele is less fit in field populations. Overall, we present a powerful platform to quantitatively assess anthelmintic resistance and effects of specific resistance alleles on organismal fitness in the presence or absence of the drug.
Highlights
All three canonical parasitic nematode beta-tubulin alleles (F167Y, E198A, F200Y) and two newly identified alleles (E198V, E198L) confer equal levels of benzimidazole resistance in a defined genetic background using single-generation, high-replication drug response assays.
Beta-tubulin variants are strongly selected in albendazole conditions in multigenerational competitive fitness assays, but these alleles confer different levels of benzimidazole resistance over time.
Only the E198V allele confers a fitness cost in control (non-benzimidazole) conditions as compared to all other tested beta-tubulin alleles, suggesting that this intermediate allele might only be found in field populations at low frequency because it causes reduced fitness.
Graphical Abstract
The anthelmintic resistance problem is widely recognized in sheep production. Therefore, new methods of control against gastrointestinal nematodes (GIN) need to be integrated. The aim of this work was to assess the toxicity of A. cina 30 CH as a homeopathic product against Haemonchus contortus in in vitro and in vivo assays. A. cina 30 CH was obtained from a commercial laboratory, and confirmation of artemisinin as a key ingredient was performed with mass spectrophotometry. The A. cina 30 CH and the artemisinin pure reagent were used for the inhibition of egg hatching (IEH) and for the inhibition of larval migration of H. contortus L3 (ILM). In addition, three groups of 10 naturally infected lambs with GIN were treated with A. cina 30 CH and albendazole, and 10 were used as control. The parasitic infection was monitored at 0, 7, 14 and 28 d postreatment (PT) to determine the number of eggs per gram (epg) and FAMACHA index. The in vitro data showed 100 % IEH and 64.7 % ILM by A. cina 30 CH, and nonlethal activity was observed with the artemisinin pure reagent. The toxicity of A. cina 30 CH against H. contortus in infected lambs was observed after 7 d of infection. Administration of the A. cina 30 CH yielded a 69 % reduction in the epg at 28 d PT, similar to the albendazole (P<0.05). In conclusion, A. cina 30 CH had the ability to IEH and ILM of H. contortus in in vitro assays and reduced the number of eggs of H. contortus, which is the primary parasitic nematode in grazing lambs, thereby reducing infection.
Strongylid gastrointestinal nematodes are an important cause of disease and economic loss in small ruminants. These parasites are important in most of the United States, with the bloodsucking parasite Haemonchus contortus being the predominant species of concern. Sheep and goats are infected while grazing, and the biology of infective larvae on pastures is important in the design of parasite management programs. Widespread resistance to anthelmintics requires strategies designed to preserve remaining drug activity; these include combination treatments with multiple classes of anthelmintics and targeted treatments.
Control of gastrointestinal nematodes has been based on anthelmintics. However, this strategy is unsustainable owing to anthelmintic resistance. Parasitic nematodes have biologic and genetic features that favor the development of drug resistance, making the emergence of resistant nematodes inevitable. The rate of resistance development is affected controllable factors. There is a need to change the paradigm of how gastrointestinal nematodes are controlled to decrease the rate at which resistance develops. This article reviews the biology and prevalence of anthelmintic resistance, and provides recommendations for diagnosing resistance and for strategies that should be implemented to reduce the development of resistance.
It is increasingly difficult to manage and control gastrointestinal nematode parasites in pasture-based ruminant livestock operations because of the high prevalence of anthelmintic resistance. Anthelmintics should be combined with alternative forms of control. Sustainable tools include copper oxide wire particles and condensed tannin-rich plants, which target primarily Haemonchus contortus in small ruminants. Nematophagous fungi reduce larvae on pasture and target nematode larvae in feces of most livestock species. In addition, and perhaps most importantly, genetic selection focuses on parasite resistance. Producers should use as many tools as possible to minimize the need for pharmaceutical interventions and optimize animal production.
Intestinal helminth parasites present major challenges to the welfare of humans and threaten the global food supply. While the discovery of anthelminthic drugs empowered our ability to offset these harms to society, the alarming rise of anthelminthic drug resistance mitigates contemporary efforts to treat and control intestinal helminthic infections. Fortunately, emerging research points to potential opportunities to combat anthelminthic drug resistance by harnessing the gut microbiome as a resource for discovering novel therapeutics and informing responsible drug administration. In this review, we highlight research that demonstrates this potential and provide rationale to support increased investment in efforts to uncover and translationally utilize knowledge about how the gut microbiome mediates intestinal helminthic infection and its outcomes.
Goats raised in pasture are inevitably infected by gastrointestinal nematodes, whatever the place and the climatic conditions. This parasitism results in production losses (growth or milk) and in some cases, in high mortality rates (with high parasite burden or in kids). For many years, these infections were controlled by conventional anthelmintics. Due to unsuitable usages (for example, high number of treatments or under-dosage), anthelmintic resistance has developed and is now very prevalent in goats as demonstrated by the numerous cases of simple or multiple anthelminthic resistance which have been reported throughout the world. Reports include resistance to the most recent anthelmintics, macrocyclic lactones and monepantel. Consequently, the way of managing gastrointestinal parasitism of goats has to move from anthelmintics alone to a more integrated management, including better use of anthelmintics, natural dewormers (nutraceuticals), enhancement of the immunity of the goats via alimentation or vaccination, selection of resistant goats or breeds and grazing management. The present chapter will give an overview of the situation regarding anthelmintic resistance in goats and integrated parasitism management.
Susceptability of Ascaridia galli to benzimidazole (BZ) was investigated using faecal egg count reduction test (FECRT), in ovo larval development test (LDT) and genetic markers (mutations at codons 167, 198 and 200 of β-tubulin gene). Six flocks (F1-F6) of a commercial laying hen farm with different number of exposure to BZ were recruited. The FECR was calculated by analyzing individual faeces (F1, F2, F4 and F5) before and 10 days after treatment. The LDT was performed on parasite eggs from pooled samples from F1 to F6 and LC50 and LC99 were calculated. DNA was extracted from 120 worms and sequenced for β-tubulin gene. In all flocks, the FECRs were above 95% (lower CI above 90%). No significant difference was observed (p > 0·05) among obtained LC50 (F1/F4 and F2/F5 vs F3/F6) in the LDT. However, LC50 and LC99 were higher than suggested values for declaration of resistance in other nematode species. No variation was observed in codon positions involved in BZ resistance. Overall, our results indicated lack of evidence of resistance to BZ in A. galli. More research is needed to confirm these results and to further optimize the existing tools for detection and monitoring of anthelmintic resistance in A. galli.
Abstract Background On two farms it was noted that after routine treatment with monepantel, fecal egg counts failed to drop. This was accompanied by lambs mortality due to Haemonchus contortus infection. The aim of this work was to evaluate the efficacy of monepantel to control gastrointestinal nematodes (GIN) in two sheep farms, in Uruguay. Findings A Fecal Egg Count Reduction Test (FECRT) was subsequently performed at the Experimental Stations Glencoe of INIA Tacuarembó (Farm 1) and Sheep Unit of INIA La Estanzuela (Farm 2) using the World Association for the Advancement of Veterinary Parasitology guidelines. On Farm 1 the FECRT was performed using 6–8 month old Corriedale or Merino Dohne x Corriedale male lambs naturally infected with GIN. On day 0 pre-treatment, three groups of 15 lambs each were selected, blocked by fecal egg count level (FEC) and randomly assigned to one of the following: Group 0 = untreated control, Group 1 = treated with monepantel (Zolvix®, Novartis Animal Health Inc.) from stock previously purchased; Group 2 = treated with monepantel from stock provided by the supplier, at the recommended dose of 2.5 mg/kg of body weight. Fecal samples were collected directly from the rectum from each lamb on day 0 and on day 9 post-treatment. On Farm 2, the FECRT was conducted on a group of 8 month old male lambs Milchschaff x Finn. At this farm, 10 lambs were randomly allocated to be treated with monepantel (Group 1) and 10 lambs were randomly allocated to remain as untreated control (Group 0) using the same protocols as Farm 1. On farm 1 the FECR was 0.0% (95% CI = 0.0 – 49.0) and 42.0% (95% CI = 0.0 – 75.0) for Group 1 and Group 2 respectively. For Farm 2, the FECR was 82.1% (95% CI = 36.0 – 99.0). Haemonchus spp was the resistant genus. Conclusions Poor effcicacy of monepantel in treating GIN parasites was demonstrated on both farms.
To determine prevalence of anthelmintic resistance on sheep and goat farms in the southeastern United States.
Cross-sectional study.
Sheep and goats from 46 farms in 8 southern states, Puerto Rico, and St Croix in the US Virgin Islands.
Parasite eggs were isolated from fecal samples, and susceptibility to benzimidazole, imidathiazole, and avermectin-milbemycin anthelmintics was evaluated with a commercial larval development assay.
Haemonchus contortus was the most common parasite on 44 of 46 farms; Trichostrongylus colubriformis was the second most commonly identified parasite. Haemonchus contortus from 45 (98%), 25 (54%), 35 (76%), and 11 (24%) farms were resistant to benzimidazole, levamisole, ivermectin, and moxidectin, respectively. Resistance to all 3 classes of anthelmintics was detected on 22 (48%) farms, and resistance to all 3 classes plus moxidectin was detected on 8 farms (17%).
Findings provided strong evidence that anthelmintic resistance is a serious problem on small ruminant farms throughout the southeastern United States. Owing to the frequent movement of animals among regions, the prevalence of resistance in other regions of the United States is likely to also be high. Consequently, testing of parasite eggs for anthelmintic resistance should be a routine part of parasite management on small ruminant farms.
Escalating anthelmintic resistance has made it essential to develop alternative ways of worm management for reducing selection for worm resistance, and one of the most promising approaches is to treat only those animals unable to cope with worm challenge, thus favouring unselected worms originating from untreated animals. Only clinical evaluation of anaemia (FAMACHA system) and the body condition score are regarded as being of practical value or having potential, respectively, for repeatedly examining flocks or herds and identifying individuals for treatment. Only the FAMACHA system has been tested well enough for use under practical farming conditions. However, further investigation is needed on its effect on animal production, and methods to reduce labour. Trials over several seasons showed that most sheep under severe Haemonchus contortus challenge required no, or only one treatment over a full summer season. A small minority (usually < 5%) needed more than two treatments. Most sheep could cope without regular treatment. With sufficient training, clinical evaluation of anaemia was found reliable for practical use. The overwhelming majority of trainees (some poorly literate) were able to implement the FAMACHA system successfully. The dynamics of haemonchosis in a flock can easily be monitored. Farmers, farm workers and veterinarians all rated the system very highly (> 80%) and treatment costs dropped by approximately 58%. The heritability of FAMACHA values obtained by clinical evaluation was high at 0.55 +/- 0.17% in a Merino stud with +/- 550 young rams and ewes which were the progeny of 21 sires. The FAMACHA system may not be as applicable to goats as to sheep, but further work is necessary. The main benefits of the system are the reduction in treatments, its use for discriminating between animals of varying ability to cope with infection (thus allowing genetic selection), and its lowering of selection pressure on H. contortus for anthelmintic resistance.
Recent studies on sheep and goat farms in the southern United States indicate that multiple-anthelmintic resistance in Haemonchus contortus is becoming a severe problem. Though many factors are involved in the evolution of resistance, the proportion of the parasite population under drug selection is believed to be the single most important factor influencing how rapidly resistance develops. Therefore, where prevention of resistance is an important parallel goal of worm control, it is recommended to leave a portion of the animals untreated. Recently, a novel system called FAMACHA was developed in South Africa, which enables clinical identification of anemic sheep and goats. When H. contortus is the primary parasitic pathogen, this system can be applied on the farm level to reduce the number of treatments administered, thereby increasing the proportion of the worm population in refugia. Since most studies validating the FAMACHA method have been performed in South Africa, it is important that the method be tested in other regions before its use is broadly recommended. We performed a validation study of FAMACHA by testing the system in sheep (n = 847) and goats (n = 537) of various breeds and ages from 39 farms located in Arkansas, Georgia, Louisiana, Florida, and the US Virgin Islands. The color of the ocular conjunctiva of all animals were scored on a 1-5 scale using the FAMACHA card, and blood samples were collected from each animal for determination of packed cell volume (PCV). Fecal samples were also collected from a majority of the animals tested for performance of fecal egg counts (FEC). Correlations between PCV and eye scores, PCV and FEC, and FEC and eye scores were all highly significant for both sheep and goats (P < 0.001). Data for both FAMACHA scores and PCV were evaluated using two separate criteria for anemia: eye score values of 3, 4 and 5 or 4 and 5, and PCV values of < or =19 or < or =15 were considered anemic. Specificity was maximized when eye score values of 4 and 5 were considered anemic and PCV cut off for anemia was < or =19, but sensitivity was low. In contrast, sensitivity was 100% for both sheep and goats when eye score values of 3, 4 and 5 were considered anemic and PCV cut off was < or =15, but specificity was low. In both sheep and goats, predictive value of a negative was greater than 92% for all anemia and eye score categories, and was greater than 99% for both eye score categories when an anemia cutoff of < or =15 was used. Predictive value of a positive test was low under all criteria indicating that many non-anemic animals would be treated using this system. However, compared to conventional dosing practices where all animals are treated, a large proportion of animals would still be left untreated. These data indicate that the FAMACHA method is an extremely useful tool for identifying anemic sheep and goats in the southern US and US Virgin Islands. However, further studies are required to determine optimal strategies for incorporating FAMACHA-based selective treatment protocols into integrated nematode control programs.
Ivermectin and moxidectin are closely related avermectin/milbemycin anthelmintics and available data suggest that side resistance occurs with these two drugs. However, moxidectin remains effective against many species of ivermectin-resistant worms due to its higher potency. The larval development assay (LDA) is routinely used to diagnose ivermectin resistance in Haemonchus contortus but laboratory diagnosis of moxidectin resistance is hampered by the lack of any validated in vitro tests. The objective of this study was to measure the relative susceptibility/resistance of H. contortus to moxidectin on goat farms in Georgia, and to validate the DrenchRite LDA for detecting resistance to moxidectin. Fecal egg count reduction tests (FECRT) were performed at five different moxidectin dose levels and DrenchRite LDAs were performed in duplicate on nine meat goat farms in Georgia, USA. To improve our ability to make inferences on the relative levels of resistance between farms, FECRT data were first analysed using a linear mixed model, and then Tukey's sequential trend test was used to evaluate the trend in response across dose levels. LDA data were analysed using log-dose logit-response and probit models. Using these statistical results, we were able to rank the nine farms from the least to the most resistant, and to develop a set of criteria for interpreting DrenchRite LDA results so that this assay can be used to diagnose both clinically apparent moxidectin resistance, as well as sub-clinical emerging resistance. These results suggest that our novel approach for examining these types of data provides a method for obtaining an increased amount of information, thus permitting a more sensitive detection of resistance. Based on results of the LDA, moxidectin-resistant farms had resistance ratios, compared with an ivermectin-sensitive farm, ranging from 32 to 128, and had resistance ratios of 6-24 compared with an ivermectin-resistant/moxidectin naive farm. Moxidectin resistance was diagnosed both in Haemonchus and Trichostrongylus on almost half of the farms tested, despite this drug only being used on these farms for 2-3 years.
In a sheep farm in the Netherlands with a suspected Haemonchus contortus resistance to monepantel (Zolvix(®), Novartis Animal Health), a fecal egg count reduction test was carried out in two groups of lambs, according to the method of the World Association for the Advancement of Veterinary Parasitology. Group 1 was the untreated control group, and group 2 was treated with monepantel at the manufacturer's recommended dose rate. Efficacy of treatment with monepantel was 0%. Larval identification of pre- and post-treatment coprocultures revealed 100% H. contortus larvae. On this farm, after a perceived reduction in efficacy of ivermectin and doramectin, the sheep farmer started using monepantel in July 2012, and since then, monepantel was used as the sole anthelmintic. Breeding sheep were treated twice each year in 2013 and 2014, and lambs two times in 2012, four times in 2013, and three times in 2014, before monepantel resistance was suspected, and confirmed three weeks later. Although the frequency of monepantel treatments on this farm was relatively high with treatments on thirteen separate occasions in two years time, possibly establishing favorable conditions for a competitive advantage for resistant H. contortus, it is remarkable that resistance to monepantel was established in such a very short period. This study confirms, to the best of our knowledge, the first case of H. contortus resistance to monepantel occurring in the field.
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After reports of the apparent failure of monepantel to reduce the egg counts of goats on a farm in the lower North Island of New Zealand, faecal egg count reduction tests were conducted in goats and lambs resident on the property, and a confirmatory, slaughter study was conducted using 12 sheep, sourced elsewhere, that were grazed on the farm for approximately 5 weeks. In the egg count reduction test in goats, 8 animals were given monepantel at 3.9mg/kg (just over 1.5× the sheep dose rate of 2.5mg/kg), whilst four received 7.7mg/kg (just over 3× the sheep dose). In the egg count reduction test in sheep, 15 lambs were treated with 3.0mg/kg of monepantel. For the confirmatory study, the sheep were housed indoors for 2 weeks before half were treated with 2.9mg/kg monepantel and the animals were killed for worm counts 9 days later. There was no evidence of efficacy in either egg count reduction test, or in the goats, the two dose rates used appeared equally ineffective. Likewise, there were no significant reductions in egg counts or worm burdens in the slaughter study. Monepantel was ineffective against at least two gastrointestinal nematode species, Teladorsagia circumcincta and Trichostrongylus colubriformis. These findings represent the first report from the field of resistance having developed to the anthelmintic monepantel with severe resistance developing in more than one species after being administered on 17 separate occasions to different stock classes and in less than 2 years of the product first being used on the farm in question.
Over the past 10-15 years, we have witnessed a rapid increase in both the prevalence and magnitude of anthelmintic resistance, and this increase appears to be a worldwide phenomenon. Reports of anthelmintic resistance to multiple drugs in individual parasite species, and in multiple parasite species across virtually all livestock hosts, are increasingly common. In addition, since the introduction of ivermectin in 1981, no novel anthelmintic classes were developed and introduced for use in livestock until recently with the launch of monepantel in New Zealand. Thus, livestock producers are often left with few options for effective treatment against many important parasite species. While new anthelmintic classes with novel mechanisms of action could potentially solve this problem, new drugs are extremely expensive to develop, and can be expected to be more expensive than older drugs. Thus, it seems clear that the "Global Worming" approach that has taken hold over the past 40-50 years must change, and livestock producers must develop a new vision for parasite control and sustainability of production. Furthermore, parasitologists must improve methods for study design and data analysis that are used for diagnosing anthelmintic resistance, especially for the fecal egg count reduction test (FECRT). Currently, standards for diagnosis of anthelmintic resistance using FECRT exist only for sheep. Lack of standards in horses and cattle and arbitrarily defined cutoffs for defining resistance, combined with inadequate analysis of the data, mean that errors in assigning resistance status are common. Similarly, the lack of standards makes it difficult to compare data among different studies. This problem needs to be addressed, because as new drugs are introduced now and in the future, the lack of alternative treatments will make early and accurate diagnosis of anthelmintic resistance increasingly important.
The data obtained from a telephone survey that targeted residents in eleven Southern states (Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, and Texas) were used to identify factors that influence goat-meat consumption by Southern consumers. The study also identifies marketing strategies that may encourage the consumption of goat-meat. This information can be used by goat-meat industry officials to better understand who their consumers are and to further expand their markets. The results from an ordered probit analysis indicated various demographic factors and consumption of other meats influenced goat-meat consumption preferences. For example, the probability of consuming goat meat increased when the respondent was over the age of 24. The results suggested the respondents' frequency of consumption for chicken, fish, and pork impacted their willingness to consume goat meat and that in-store displays and price specials would be effective marketing strategies.
Consumption or likely consumption of goat-meat products is influenced by age, household size, religion, race, gender, and geographic location. Consumers of goat meat are more likely to be older, to live in households with three or more persons, or to be non-Caucasians or Texas residents. The most likely consumers of goat nuggets, patties, roasts, or packaged, ready-to-cook goat meat are from households with three or more persons, or are Catholics, non-Caucasians, men, or Texas residents.
Methods have been described to assist in the detection of anthelmintic resistance in strongylid nematodes of ruminants, horses and pigs. Two tests are recommended, an in vivo test, the faecal egg count reduction test for use in infected animals, and an in vitro test, the egg hatch test for detection of benzimidazole resistance in nematodes that hatch shortly after embryonation. Anaerobic storage for submission of faecal samples from the field for use in the in vitro test is of value and the procedure is described. The tests should enable comparable data to be obtained in surveys in all parts of the world.
The relationship between resistance detected in the faecal egg count reduction test (FECRT) and the lethal dose 50% (LD50) in the egg hatch assay (EHA) for benzimidazoles (BZs) and a larval development assay (LDA) for BZs, levamisole (LEV) and ivermectin (IVM) was examined on 13 sheep farms and 12 goat farms in Denmark. Out of 10 farms where resistance to BZs was detected according to the FECRT, nine (90%) had LD50 values above 0.5 microM thiabendazole (TBZ) (0.1 microg TBZ/ml) in the EHA, indicating resistance to BZs. However, four out of the 12 isolates susceptible to BZs in the FECRT had LD50 values higher than 0.5 microM TBZ in the EHA. For all isolates examined, LD50 values for TBZ in the LDA were lower than in the EHA. Four out of 11 and five out of 12 farms with worm populations resistant to BZs according to the FECRT and EHA respectively, had LD50 values lower than 0.5 microM TBZ in the LDA. Using the same cut-off point for resistant isolates in the LDA as in the EHA (0.5 microM TBZ), these isolates would be considered susceptible to BZs. All 10 isolates susceptible to BZs according to the FECRT and EHA and two isolates with suspect BZ resistance had LD50 values lower than 0.5 microM TBZ in the LDA. The above results indicated fairly good agreement in the detection of BZ resistance between the FECRT, EHA and the LDA. Groups of farms where resistance to LEV was detected according to the FECRT had higher mean LD50 values compared to those with LEV-susceptible or suspected resistant isolates. However, only four out of 12 farms having isolates resistant to LEV had LD50 values higher than 1.2 microM LEV (0.28 microg LEV/ml) recorded previously for a LEV-susceptible strain of Ostertagia circumcincta. This indicated discrepancies in declaring resistance to LEV between the FECRT and the LDA. Isolates from four farms where resistance to IVM was detected in the FECRT had LD50 values higher than the susceptible isolates. These were 2.5 to 7.5 times higher than those recorded previously for IVM-susceptible strains.
Anthelmintic resistance was monitored over a 30 month period within a goat herd in eastern Virginia, USA. Resistance to ivermectin, levamisole and benzimidazole drugs was detected in Haemonchus contortus using the fecal egg count reduction test (FECRT). When levamisole use was discontinued for 1 year, susceptibility to levamisole appeared to return. Although a single treatment with fenbendazole was able to reduce fecal egg counts by only 50%, two doses administered in a 12 h interval increased efficacy to 92%, however, confidence intervals indicated that resistance was still present. When fecal egg counts were determined the following year after several treatment using this protocol, the efficacy of fenbendazole had fallen again to 57% reduction in fecal egg counts. The predominant genus present in cultured composite fecal samples was Haemonchus. Trichostrongylus, Cooperia and Teladorsagia were also present in smaller numbers.
Gastrointestinal nematode (GIN) parasitism is a major constraint to production of goats in the southeastern United States. The conventional method of control used by producers in this region is frequent use of anthelmintics during the warm season. Overuse of anthelmintics has led to an increase in the incidence of anthelmintic resistance in many parts of the world, but data on prevalence of anthelmintic resistance in GIN of goats in the southeastern United States are very limited. To address this issue, anthelmintic efficacy was determined in goat herds at the Fort Valley State University, Agricultural Research Station (FVSU-ARS) and the University of Georgia, College of Veterinary Medicine (UGA-CVM) using fecal egg count reduction (FECR) tests and DrenchRite((R)) larval development assays (LDA). At FVSU-ARS, 2-year-old Spanish goat does were randomly allocated to one of nine different treatment groups (n = 10): albendazole (ABZ; 20mg/kg body weight (BW)), fenbendazole (FBZ; 20mg/kg BW), ivermectin (IVM; 0.4 mg/kg BW), doramectin (DRM; 0.4 mg/kg BW), moxidectin (MOX; 0.4 mg/kg BW), levamisole (LEV; 12 mg/kg BW), morantel tartrate (MOR; 10mg/kg BW), a combination of IVM (0.4 mg/kg BW) and ABZ (20 mg/kg BW), and untreated controls. At UGA-CVM, goats were randomly allocated to one of five different treatment groups (n = 8): ABZ (20 mg/kg BW), IVM (0.4 mg/kg BW), MOX (0.4 mg/kg BW), LEV (12 mg/kg BW), and untreated controls. All drugs in both experiments were administered orally. Anthelmintic efficacy was calculated by comparing 14-day post-treatment FEC of treated and control animals, and percent reductions were interpreted using the World Association for the Advancement of Veterinary Parasitology guidelines for resistance. For the LDA, nematode eggs were isolated from pooled fecal samples of untreated control goats in each herd and used to perform DrenchRite((R)) assays. In the FVSU-ARS herd, MOX, LEV, the combination of IVM and ABZ, IVM, DRM, ABZ, MOR, and FBZ reduced FEC by 100, 91, 88, 78, 76, 62, 48, and 10%, respectively. In the UGA-CVM herd, MOX, LEV, ABZ and IVM, reduced FEC by 100, 94, 87, and 0%, respectively. In both herds moxidectin was the only drug tested that was fully effective. Results of the LDA were in agreement with results of the FECR tests for both herds. These data demonstrate the presence of GINs resistant to all three major anthelmintic classes in both goat herds.
To determine prevalence of resistance to all anthelmintics that are commonly used to treat gastrointestinal nematodes (GINs) in goats.
Prospective study.
777 goats.
On each farm, goats were assigned to 1 of 5 treatment groups: untreated controls, albendazole (20 mg/kg [9.0 mg/lb], p.o., once), ivermectin (0.4 mg/kg [0.18 mg/lb], p.o., once), levamisole (12 mg/kg [5.4 mg/lb], p.o., once), or moxidectin (0.4 mg/kg, p.o., once), except on 3 farms where albendazole was omitted. Fecal samples were collected 2 weeks after treatment for determination of fecal egg counts (FECs), and percentage reductions were calculated by comparing data from anthelmintic-treated and control groups. Nematode populations were categorized as susceptible, suspected resistant, or resistant by use of guidelines published by the World Association for the Advancement of Veterinary Parasitology.
Resistance to albendazole was found on 14 of 15 farms, and resistance to ivermectin, levamisole, and moxidectin was found on 17, 6, and 1 of 18 farms, respectively. Suspected resistance to levamisole and moxidectin was found on 4 and 3 farms, respectively. Resistance to multiple anthelmintics (albendazole and ivermectin) was found on 14 of 15 farms and to albendazole, ivermectin, and levamisole on 5 of 15 farms. Mean overall FEC reduction percentages for albendazole, ivermectin, levamisole, and moxidectin were 67, 54, 94, and 99%, respectively.
Anthelmintic resistance in GINs of goats is highly prevalent in the southern United States. The high prevalence of resistance to multiple anthelmintics emphasizes the need for reexamination of nematode control practices.
A larval development assay (LDA, DrenchRite) was evaluated to determine the effectiveness of this method in detecting anthelmintic resistance in cyathostomin nematodes of horses. A total of 15 horse farms from Georgia and South Carolina (USA) and Population S ponies from the University of Kentucky (USA) were included in this study. Nematode eggs were extracted from pooled fecal samples and placed into the wells of a DrenchRite plate for testing against thiabendazole (TBZ), levamisole (LEV) and 2 ivermectin (IVM) analogs (IVM-1, IVM-2). After a 7-day incubation larvae in each well were counted and data were analyzed by logistic regression. Resistance status of each farm for different drugs was determined in a separate study using a fecal egg count reduction test. LDA were performed on the 15 farms once, however, the Population S cyathostomins were assayed on 3 separate occasions to estimate the consistency of results between assays. Mean TBZ LC50 for oxibendazole resistant, suspected resistant and sensitive farms were 0.2015, 0.1625, and 0.1355 microM, respectively. For LEV, mean LC50 for PYR resistant, suspected resistant and sensitive farms were 1.590, 1.8018 and 1.4219 microM, respectively. All 15 farms had worms susceptible to IVM; mean LC50 for IVM-1 and for IVM-2 were 7.5727 and 87.9718 nM, respectively. A linear mixed model was fitted to the data to determine the relationship between LC50 and LC95 and resistance status for each farm. No meaningful relations were found. Consistency of assays varied between drugs, being best for TBZ and worst for LEV and IVM-1. All farms in this study had benzimidazole-resistant nematodes; therefore usefulness of DrenchRite for discriminating susceptibility versus resistance to this drug class could not be accurately assessed. Moreover, since all farms tested were sensitive to IVM and resistance to this drug class has not yet been reported in cyathostomins, it is not possible to assess accurately the usefulness of DrenchRite LDA for detecting IVM resistance at this time. Assay results for LEV suggest that LEV in a LDA does not yield data that is useful in estimating PYR efficacy in vivo. Based on results for PYR/LEV, the current high prevalence of benzimidazole resistance, no known cases of IVM resistance, and the sometimes extreme variation in results seen in many of the assays, DrenchRite LDA cannot be considered a useful tool for the diagnosis of resistance in cyathostomins of horses at present.
Reports of drug resistance have been made in every livestock host and to every anthelmintic class. In some regions of world, the extremely high prevalence of multi-drug resistance (MDR) in nematodes of sheep and goats threatens the viability of small-ruminant industries. Resistance in nematodes of horses and cattle has not yet reached the levels seen in small ruminants, but evidence suggests that the problems of resistance, including MDR worms, are also increasing in these hosts. There is an urgent need to develop both novel non-chemical approaches for parasite control and molecular assays capable of detecting resistant worms.
Seriously escalating global anthelmintic resistance in gastrointestinal nematodes of small ruminants has spawned a variety of alternatives to anthelmintics for worm management, based on the need for sustainable Integrated Parasite Management (sIPM). Pivotal to the sIPM approach is the concept of refugia, the proportion of a given parasite population that escapes exposure to control measures. By balancing drug applications with the maintenance of refugia, the accumulation of anthelmintic resistance alleles in worm populations can be considerably delayed, while still providing good levels of control. The over-dispersed nature of parasitic infections provides an opportunity to achieve this balance, by targeting treatments to the members of a flock or herd that are least tolerant to nematode infection. However, implementation of this strategy has only recently become feasible, with the development of the FAMACHA((c)) system for clinical evaluation of anaemia due to haemonchosis. Subsequently, the use of milk yields has proven an effective indicator in dairy goats infected predominantly with nematodes other than Haemonchus contortus. In addition, short-term weight changes and perhaps also body condition scoring may provide indices of parasitism, permitting the rapid identification of animals likely to benefit from treatment. However, sIPM and refugia-based approaches are more complex than whole-flock treatments in conventional programs, and adoption by farmers is most likely where the theoretical basis is understood. As close communication with informed advisors is generally limited, there is a danger that sIPM will remain a theoretical concept without alternative modes of communication. The development of computer-based decision support programs, which use epidemiological, seasonal and clinical information to provide recommendations for specific situations, should be accorded high priority in the future development of worm management systems.
Some modifications of the McMaster helminth egg-counting technique and apparatus
- Whitlock
Whitlock, H.V., 1948. Some modifications of the McMaster helminth egg-counting
technique and apparatus. J. Counc. Sci. Ind. Res. 21 (1948), 177-180.
DrenchRite™, Larval Development Assay Standard Operating Procedures Horizon Technology Pty Limited
- Anon
Anon., 1996. DrenchRite TM, Larval Development Assay Standard Operating
Procedures Horizon Technology Pty Limited, Roseville, Australia, 29 pp.