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Genetics and infection dynamics of Paratrichosoma sp in farmed saltwater crocodiles (Crocodylus porosus)
Abstract
Paratrichosoma-associated helminthiasis has been identified in saltwater crocodiles under intensive farming conditions. The development of sustainable integrated management practices is dependent on a detailed understanding of Paratrichosoma population genetics and infection dynamics. This study investigated the genetic relationships of Paratrichosoma sp in a population of commercially farmed saltwater crocodiles, Crocodylus porosus, in northern Australia. 18S ribosomal RNA gene sequence data were obtained from Paratrichosoma sp eggs present in the epidermis of infected animals. A high level of genetic diversity was distributed within the Paratrichosoma sp population (241 variable positions in the 1094 bp alignment), indicating an accelerated rate of nucleotide base-pair substitutions in this genus of nematodes. Several possible environmental correlates of the incidence and intensity of helminthiasis, including season, rainfall, and mean monthly temperature, were investigated by visual inspection of crocodile skins. Stepwise logistic regression revealed a significant negative linear relationship (P = 0.011, R
2 = 32.69 %) between mean monthly rainfall and the incidence of monthly Paratrichosoma-associated helminthiasis. Variation in the severity of Paratrichosoma-associated helminthiasis could not be explained by any of the independent environmental variables included within an ordinal regression analysis. The large genetic diversity in these nematodes indicates a high probability of anthelmintic resistant alleles occurring in the population. We discuss how the spread of these alleles may be mitigated by adopting targeted treatment protocols.
... However, tell-tale characteristics of Paratrichosoma infection have been detected in eight of the crocodilians species, including the commercially significant C. niloticus and C. porosus (Tellez and Paquet-Durand, 2011). The genus has a cosmopolitan distribution, having been reported in such diverse locations as Africa, the Americas, Southern Asia and Australia (Webb and Messel, 1977;Webb and Manolis, 1983;Spratt, 1985;Whitaker and Andrews, 1989;Moravec and Vargas-Vazquez, 1998;Lott et al., 2015). ...
... The incidence of Paratrichosoma-associated helminthosis in C. porosus has been shown to increase during periods of low rainfall. It has been speculated that the shedding of eggs in some Paratrichosoma species may have evolved to coincide when the bodies of water that crocodiles occupy are smallest, and host population density is correspondingly higher, thereby aiding transmission (Lott et al., 2015). ...
... This type of housing raises the production costs but since the efficacy of broad-spectrum anthelmintics remains unknown, there are no confirmed treatments for Paratrichosoma. Evidence of unusually high genetic diversity in some Paratrichosoma populations suggests that the occurrence and spread of anthelmintic resistant alleles may be a primary management concern in this genus of parasites (Lott et al., 2015). Restricting the application of broad-spectrum anthelmintics to individuals most at risk of developing Paratrichosoma-associated helminthosis may minimise the impact of the parasite on the productivity of commercial farming operations while simultaneously forestalling the spread of anthelmintic resistance. ...
Genetic management is a critical component of threatened species conservation. Understanding spatial patterns of genetic diversity is essential for evaluating the resilience of fragmented populations to accelerating anthropogenic threats. Nowhere is this more relevant than on the Australian continent, which is experiencing an ongoing loss of biodiversity that exceeds any other developed nation. Using a proprietary genome complexity reduction‐based method (DArTSeq), we generated a data set of 3239 high quality Single Nucleotide Polymorphisms (SNPs) to investigate spatial patterns and indices of genetic diversity in the koala (Phascolarctos cinereus), a highly specialised folivorous marsupial that is experiencing rapid and widespread population declines across much of its former range. Our findings demonstrate that current management divisions across the state of New South Wales (NSW) do not fully represent the distribution of genetic diversity among extant koala populations, and that care must be taken to ensure that translocation paradigms based on these frameworks do not inadvertently restrict gene flow between populations and regions that were historically interconnected. We also recommend that koala populations should be prioritised for conservation action based on the scale and severity of the threatening processes that they are currently faced with, rather than placing too much emphasis on their perceived value (e.g., as reservoirs of potentially adaptive alleles), as our data indicate that existing genetic variation in koalas is primarily partitioned among individual animals. As such, the extirpation of koalas from any part of their range represents a potentially critical reduction of genetic diversity for this iconic Australian species.
This chapter presents an overview of the clinical signs and major disease syndromes affecting captive and wild reptiles (marine and freshwater turtles, crocodilians, marine iguanas and sea snakes).
Paratrichosma spp. are capillarid worms that parasitize the abdominal skin of crocodiles. They are likely not a threat to crocodiles’ health but they affect the commercial value of their skin. No successful treatment exists against this parasite, and present knowledge on its life cycle is limited. Herein we report new information on Paratrichosoma recurvum occurrence in wild American crocodiles Crocodylus acutus from Mexican Caribbean islands and its relation with environmental (water salinity, temperature, climatic events) and biological (body condition) factors. The percentage of parasitized crocodiles (30.3%) is among the highest recorded in wild crocodilian populations. Small (<40.8 cm total length [TL]) and large (>270 cm TL) crocodiles are less parasitized, probably due to the characteristics of their skin or of the parasite life cycle. Two individuals showed to have wormed naturally between their capture and recapture. Thorax-abdomen is the most parasitized body part of crocodiles. The infection risk is not associated with the sex of the crocodile, but there was a difference in the proportion of parasitized crocodiles between sites, which could be related to different environmental conditions. The body condition of a crocodile does not seem to be affected by the parasite. Climatic events and water temperature show no effect on the parasitism of crocodiles but salinity could have one. The infection of crocodiles by P. recurvum could depend more on an individual’s behavior than on environmental conditions.
Field and experimental evidence of a new caiman trypanosome species closely phylogenetically related to fish trypanosomes and transmitted by leeches,
Minimising stress in farmed crocodiles is not only important for improving animal welfare, but may also improve skin blemish healing and infection resistance, which influence the quality of the final skin product. Forty near-harvest size saltwater crocodiles (1.6-1.8 m TL) from two Australian farms were sampled to evaluate the effect of different pen types (communal pens n=20; individual pens n=20) on stress as indicated by plasma corticosterone. Blood samples were taken within three minutes of immobilisation and analysed using a commercial enzyme immunoassay kit. There was no relationship with animal size (P=0.16), between farms (P=0.86), pen types (P=0.69), communal pens between farms (P=0.28) or individual pens between farms (P=0.24). Based on corticosterone levels, it appears that individual pens do not cause significantly more stress on harvest-size animals than communal pens. Individual pens meet their design specifications by achieving comparable healing rates of belly skin blemishes as communal pens without compromising animal welfare and minimising the possibility of new blemishes.
Four morphospecies of Cloacina, parasitic nematodes in the stomachs of rock wallabies (Petrogale spp.) from Queensland, were compared genetically using sequence data of the two internal transcribed spacers of nuclear ribosomal DNA (rDNA). The results suggest that two geographically isolated populations of C. ernabella from P. purpureicollis were genetically distinct. Based on the autapomorphic species concept, these two C. ernabella populations represented different species. For the three other nematode morphospecies, there were genetic differences among individuals of a morphospecies present in different species of host. The results suggest that each may represent a complex of sibling species, with a different species present in each species of rock wallaby examined for that morphospecies. In the C. caenis and C. pearsoni complexes, the lineage present in P. purpureicollis from western Queensland represents a sister taxon to those in the P. pencillata complex from the east coast. In the C. robertsi complex, the taxon parasitic in P. persephone represents the sister taxon to those in the P. pencillata complex and in P. purpureicollis. C. robertsi was found for the first time in P. purpureicollis from Winton in central Queensland, suggesting contact in the recent past between populations of P. purpureicollis and a member of the P. penicillata complex.
Examples of nematodes parasitizing the ventral scales of Crocodylus acutus and Crocodylus moreletii in southern Belize were observed via health assessments performed on crocodiles at the American Crocodile Education Sanctuary in Punta Gorda, Belize, in August 2009. Indirect identification was based on physical imprints of the parasite on the epidermis, and zigzag scars caused by movement and egg discharge from the skin into the surrounding environment. These observations in Belize are similar to those of documented cases of Paratrichosoma Ashford and Muller 1978 (Nematoda: Trichosomoididae) found on the ventral scales of crocodiles in Mexico, Asia, and Australia.
A new statistical method for estimating divergence dates of species from DNA sequence data by a molecular clock approach is developed. This method takes into account effectively the information contained in a set of DNA sequence data. The molecular clock of mitochondrial DNA (mtDNA) was calibrated by setting the date of divergence between primates and ungulates at the Cretaceous-Tertiary boundary (65 million years ago), when the extinction of dinosaurs occurred. A generalized leastsquares method was applied in fitting a model to mtDNA sequence data, and the clock gave dates of 92.311.7, 13.31.5, 10.91.2, 3.70.6, and 2.70.6 million years ago (where the second of each pair of numbers is the standard deviation) for the separation of mouse, gibbon, orangutan, gorilla, and chimpanzee, respectively, from the line leading to humans. Although there is some uncertainty in the clock, this dating may pose a problem for the widely believed hypothesis that the bipedal creatureAustralopithecus afarensis, which lived some 3.7 million years ago at Laetoli in Tanzania and at Hadar in Ethiopia, was ancestral to man and evolved after the human-ape splitting. Another likelier possibility is that mtDNA was transferred through hybridization between a proto-human and a protochimpanzee after the former had developed bipedalism.
A longitudinal study of nematode infection in chimpanzees was conducted between 1989 and 1994 on the M group chimpanzees of
the Mahale Mountains National Park, Tanzania during two annual dry and rainy season periods and a third rainy season. Chemical
and physical antiparasite properties of medicinal plant use against the strongyle nematodeOesophagostomum stephanostomum have recently been reported at Mahale. Here, the incidence of nematode infections were analyzed for seasonal trends to elucidate
the possible influence of parasite infection on previously reported seasonality of medicinal plant use and to test the hypothesis
that the use of these plants is stimulated byO. stephanostomum. The number of chimpanzees infected byO. stephanostomum was significantly higher in the rainy season than in the dry season of both 1989–1990 and 1991–1992. However, the incidence
ofTrichuris trichura andStrongyloides fuelleborni showed no seasonality. Reinfection of individuals byO. stephanostomum occurred in synchrony with annual variation in rainfall: there was a sharp rise in the occurrence of new infections per individual
within one to two months after the beginning of the first heavy rains of the season. This pattern coincides with the reproductive
cycle of this nematode species.O. stephanostomum (95%) infections were associated significantly more frequently with medicinal plant use than eitherT. trichiura (50%) orS. fuelleborni (40%) infections. These observations are consistent with previous reports for the increased use of these plants during the
rainy season and are consistent the hypothesis that medicinal plant use is stimulated byO. stephanostomum infection.
The program MRBAYES performs Bayesian inference of
phylogeny using a variant of Markov chain Monte Carlo.
Availability: MRBAYES, including the source code, documentation,
sample data files, and an executable, is available at http://brahms.biology.rochester.edu/software.html.
Contact: johnh{at}brahms.biology.rochester.edu
1. The estuarine crocodile (Crocodylus porosus) is the world’s largest living reptile. It predominately inhabits freshwater and estuarine habitats, but widespread geographic distribution throughout oceanic islands of the South-east Pacific suggests that individuals undertake sizeable ocean voyages.
2. Here we show that adult C. porosus adopt behavioural strategies to utilise surface water currents during long-distance travel, enabling them to move quickly and efficiently over considerable distances.
3. We used acoustic telemetry to monitor crocodile movement throughout 63 km of river, and found that when individuals engaged in a long-distance, constant direction journey (>10 km day−1), they would only travel when current flow direction was favourable. Depth and temperature measurements from implanted transmitters showed that they remained at the water surface during travel but would dive to the river substratum or climb out on the river bank if current flow direction became unfavourable.
4. Satellite positional fixes from tagged crocodiles engaged in ocean travel were overlaid with residual surface current (RSC) estimates. The data showed a strong correlation existed between the bearing of the RSC and that of the travelling crocodile (r2 = 0·92, P < 0·0001).
5. The study demonstrates that C. porosus dramatically increase their travel potential by riding surface currents, providing an effective dispersal strategy for this species.
Reported is the seasonal pattern of Opisthorchis viverrini metacercariae in cyprinoid fish in north-east Thailand. Samples of fish were collected in 1991-92 at monthly intervals from two areas-Khon Kaen Province, where the opisthorchiasis transmission rate was high, and Mahasarakham Province, where the rate was low. Metacercarial loads in both study areas had similar seasonal patterns. High burdens occurred in the late rainy season and winter (July to January) with low burdens during the summer (March to June). The average burden for Puntius leiacanthus in Khon Kaen was 1.68 metacercariae per fish (127.43 per kg), higher than for all species of cyprinoid fish from the low transmission area. The intensities of infection among P. leiacanthus and Cyclocheilichthys armatus collected in Mahasarakham were comparable, but lower than the intensity of Hampala dispar (0.75 metacercariae per fish) concurrently sampled from the same area (P < 0.05). There was no significant difference in metacercarial load per kg between fish species from Mahasarakham. The results indicate that seasonal variation in metacercariae was a common phenomenon in areas with both high and low endemicity of infection. Also, the metacerarial load in fish was positively associated with infection levels among humans.
MrBayes 3 performs Bayesian phylogenetic analysis combining information from different data partitions or subsets evolving under different stochastic evolutionary models. This allows the user to analyze heterogeneous data sets consisting of different data types—e.g. morphological, nucleotide, and protein—and to explore a wide variety of structured models mixing partition-unique and shared parameters. The program employs MPI to parallelize Metropolis coupling on Macintosh or UNIX clusters.
Availability: http://morphbank.ebc.uu.se/mrbayes
Contact: fredrik.ronquist@ebc.uu.se
*
To whom correspondence should be addressed.
Inference of evolutionary relationships between nematodes is severely hampered by their conserved morphology, the high frequency of homoplasy, and the scarcity of phylum-wide molecular data. To study the origin of nematode radiation and to unravel the phylogenetic relationships between distantly related species, 339 nearly full-length small-subunit rDNA sequences were analyzed from a diverse range of nematodes. Bayesian inference revealed a backbone comprising 12 consecutive dichotomies that subdivided the phylum Nematoda into 12 clades. The most basal clade is dominated by the subclass Enoplia, and members of the order Triplonchida occupy positions most close to the common ancestor of the nematodes. Crown Clades 8-12, a group formerly indicated as "Secernentea" that includes Caenorhabditis elegans and virtually all major plant and animal parasites, show significantly higher nucleotide substitution rates than the more basal Clades 1-7. Accelerated substitution rates are associated with parasitic lifestyles (Clades 8 and 12) or short generation times (Clades 9-11). The relatively high substitution rates in the distal clades resulted in numerous autapomorphies that allow in most cases DNA barcode-based species identification. Teratocephalus, a genus comprising terrestrial bacterivores, was shown to be most close to the starting point of Secernentean radiation. Notably, fungal feeding nematodes were exclusively found basal to or as sister taxon next to the 3 groups of plant parasitic nematodes, namely, Trichodoridae, Longidoridae, and Tylenchomorpha. The exclusive common presence of fungivorous and plant parasitic nematodes supports a long-standing hypothesis that states that plant parasitic nematodes arose from fungivorous ancestors.
Identifying factors which regulate temporal and regional structuring within parasite assemblages requires the development of non-invasive techniques which facilitate both the rapid discrimination of individual parasites and the capacity to monitor entire parasite communities across time and space. To this end, we have developed and evaluated a rapid fluorescence-based method, terminal restriction fragment length polymorphism (T-RFLP) analysis, for the characterisation of parasitic nematode assemblages in macropodid marsupials. The accuracy with which T-RFLP was capable of distinguishing between the constituent taxa of a parasite community was assessed by comparing sequence data from two loci (the ITS+ region of nuclear ribosomal DNA and the mitochondrial CO1) across ∼20 species of nematodes (suborder Strongylida). Our results demonstrate that with fluorescent labelling of the forward and reverse terminal restriction fragments (T-RFs) of the ITS+ region, the restriction enzyme Hinf1 was capable of generating species specific T-RFLP profiles. A notable exception was within the genus Cloacina, in which closely related species often shared identical T-RFs. This may be a consequence of the group's comparatively recent evolutionary radiation. While the CO1 displayed higher sequence diversity than the ITS+, the subsequent T-RFLP profiles were taxonomically inconsistent and could not be used to further differentiate species within Cloacina. Additionally, several of the ITS+ derived T-RFLP profiles exhibited unexpected secondary peaks, possibly as a consequence of the restriction enzymes inability to cleave partially single stranded amplicons. These data suggest that the question of T-RFLPs utility in monitoring parasite communities cannot be addressed without considering the ecology and unique evolutionary history of the constituent taxa.
Crocodilians throughout the world are under very heavy pressure from habitat destruction, human displacement and deliberate hunting for skins. In Papua New Guinea crocodiles of two species are still relatively plentiful and play an important part in the economy of many remote settlements. An attempt is being made by the national government to implement a policy intended to bring about the harvesting of wild crocodiles on a sustained yield basis and provide an economic incentive for conserving wild stocks in their natural habitat. Low human population density and the existence of vast swamplands make this a possibility. In recognition of the policy and the exceptional circumstances, Papua New Guinea has been exempted from trade restrictions imposed by a number of countries under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
Abstract A set of polymerase chain reaction primers were designed, which amplify a c. 1 kb fragment of the 18S ribosomal DNA gene, and are specific to the phylum Nematoda. These have proven useful in isolating nematode genes from samples mixed with other biological material, particularly with application to DNA barcoding. Optimal reaction conditions are described. These primers have successfully amplified the correct fragment from a wide phylogenetic range of nematodes, and have so far generated no sequences from any other organismal group.
Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, NY 10460, U.S.A., email jcaiman@aol.com
Crocodile farming is an important and lucrative activity in Zimbabwe which provides meat for human consumption and skins for the luxury leather industry. Because it gives an economic value to this otherwise unfriendly animal, farming crocodiles has a positive side effect on the conservation of this species in the wild. This paper gives an overview of the crocodile industry in Zimbabwe.
Commercial crocodile rearing stations in Rhodesia are described, including regulations which govern their operation. When crocodile eggs are collected from the wild a quota of juveniles equivalent to 5% of the number collected must be released at the age of 3 years. Figures for hatching success and juvenile growth on rearing stations compared with wild populations indicate that both these parameters are better on the rearing stations. The growth rate on a rearing station is twice as fast as in the wild. Data on juvenile survival on the rearing stations suggest that it is of the order of 50% to the age of 3 years. No comparative information is available for wild populations. Survival of station-reared crocodiles after release into the wild is good, although growth slows substantially. Juveniles for release are a valuable tool in management, for restocking suitable areas or supplementation of natural recruitment. Crocodile farms may provide an answer to future management of this species, and a ready source of breeding stock is available in ‘problem’ animals which are relocated rather than shot. Crocodile rearing and farming in developing countries could provide the incentive to maintain a renewable resource rather than to exploit and destroy existing populations.
Three new species of Pristionchus (P. exspectatus, P. arcanus, and P. japonicus) are described from Japan. They are morphologically similar, with P. exspectatus and P. arcanus being almost indistinguishable from the model organism P. pacificus. Reproductive isolation, namely the inability to produce interfertile F1 hybrids, separates all species pairs in the species complex. Additionally, all three new species are distinguished from P. pacificus Sommer, Carta, Kim, and Sternberg, 1996 by having a gonochoristic instead of hermaphroditic mode of reproduction. In addition to its reproductive isolation, P. japonicus is distinct from other Pristionchus species by its arrangement of genital papillae. All species in the complex are separated from each other by molecular sequence divergence, as indicated by analysis of 27 nuclear protein-coding genes and unique sequences of the small subunit ribosomal RNA gene. The identification of a species complex that includes P. pacificus is invaluable for studies of population genetics, speciation, and macroevolution, particularly the evolution of hermaphroditism in the genus.
Due to their particular way of life, dispersal of parasites is often mediated by their host's biology. Dispersal distance is relevant for parasites because high degree of dispersal leads to high gene flow, which counters the rate of parasite local adaptation in the host populations. Parasites with complex life cycles need to exploit sequentially more than one host species to complete their life cycle. Most trematode parasites have such complex life cycles involving invertebrate and vertebrate hosts. The spatial scales of invertebrate and vertebrate host populations are often different, which may decrease the probability that the parasite cycles locally in the intermediate host population. We used neutral microsatellite markers to determine genetic structure in Diplostomum pseudospathaceum parasites collected from local populations of freshwater snails (Lymnaea stagnalis). D. pseudospathaceum is a trematode that has two intermediate hosts (snail and fish) and a highly motile definitive host (bird). We found that the parasite population infecting the local snail populations showed no genetic structure over a large geographic range (over 300km). We also did not detect evidence for isolation by distance in the parasite. We conclude that dispersal in the motile definitive host is likely to prevent emergence of local population genetic structure in the parasite. Our results suggest that parasite dispersal in the definitive host may limit local cycling of the parasites in the intermediate host populations.
Anthelmintic resistance is recognised as a major problem affecting small ruminant production worldwide and now threatens the sustainability of many of these systems. One method that has been proposed to prolong the efficacy of our current anthelmintics is the maintenance of a parasite population in refugia (unexposed to a drug) which will maintain the genes for susceptibility within the parasite population. Management strategies that employ refugia-based methods include targeted or strategically timed whole flock treatments, targeted selective treatments (TST), whereby only a proportion of the flock is treated at any one time, and the dilution of resistant with susceptible parasites. The ability to effectively target anthelmintic use relies on the identification of those animals that will most benefit from treatment. This review explains the concept of refugia, describes the role of refugia-based approaches to the management of anthelmintic resistance and reviews the markers that have been studied as indicators for TSTs as well as the implementation of refugia-based strategies. Recent results suggest that targeting anthelmintic treatment on the basis of anaemia, milk production and liveweight gain may offer a means of reducing anthelmintic usage whilst still maintaining animal performance.
Four hyper-variable regions (HVR-I to -IV) found in 18S ribosomal DNA sequences were compared among 34 isolates of 15 species of the genus Strongyloides to evaluate their diagnostic value. HVR-I to -III were short, and plural species exhibit the same nucleotide arrangement. Meanwhile, HVR-IV had 23 to 39 nucleotides, showing species-specific arrangements, except Strongyloides ransomi and Strongyloides venezuelensis, which had the same nucleotide sequence in HVR-IV but were readily distinguished by the difference in HVR-I and -III. Isolates of Strongyloides stercoralis from humans of USA, Japan, and Philippines, chimpanzees, and dogs had an identical sequence in this region. Meanwhile, intraspecific polymorphism in HVR-IV nucleotide arrangement was observed among isolates of Strongyloides fuelleborni and Strongyloides callosciureus, presumably reflecting process of geographical dispersal and adaptation to the hosts.
A new genus of nematode (Paractrichosoma crocodilus) is described from Crocodilus novaeguinae. Adults have typical trichuroid features but elongated stichocytes (over 1 mm in female). Males are one third to one half as long as females and have no spicule or sheath.
The magnitude of production losses and the epidemiology and control of gastro-intestinal nematodes, fascioliasis and paramphistomiasis in sheep, goats and cattle and of Onchocerca gutturosa and Cysticercus bovis in cattle in tropical regions is reviewed in broad terms.The limited information available indicates tremendous losses caused by gastro-intestinal nematodes. Acute outbreaks are commonly seen in the wet season in animals grazing at moderate to high densities. Control is commonly by anthelmintic medication but is limited by the cost of treatment.Fascioliasis causes enormous losses; acute outbreaks are generally seen in the mid-dry season in West Africa. Anthelmintic medication is the major means of control but in most cases drugs are applied haphazardly. Intestinal paramphistomiasis is responsible for some losses; the epidemiology of the disease is essentially as described for fascioliasis, but attempts at control are negligible.Although Onchocerca gutturasa causes considerable losses in cattle, little is known about its epidemiology and control attempts are rare.Cysticercus bovis causes losses in cattle. The habit of eating grilled meat, lack of meat inspection facilities and reluctance of infected persons to seek treatment are responsible for the perpetuation of infection.
This chapter reviews the role of hypobiosis in the biology of nematodes. Successful transfer from an infected host to a susceptible one represents a most important achievement in the parasitic way of life. Any developmental adaptation that serves to facilitate this process is, therefore, extremely important in the epidemiology of these infections. Hypobiosis or facultative arrested development represents such an adaptation which, by facilitating the persistence of the larval forms for prolonged periods in the host, enables the parasite to capitalize on optimal opportunities for transfer. The phenomenon appears to be widespread among parasitic organisms. The chapter considers several aspects of this phenomenon as the species involved, factors associated with its induction as well as those influencing a resumption of development, implications of the phenomenon for understanding the epidemiology of these conditions, and its adaptive and population regulatory significance. Host resistance causes the arrested development and that resumption of development is a result of the relaxation of immunity. It is considered to be a host-regulated phenomenon that served to limit the size and pathogenicity of the population of worms, which is accumulating during the season of increasing larval availability. The chapter describes the types of hypobiosis, which include immune-mediated arrest and seasonally induced arrest.
The nucleotide sequence of the second internal transcribed spacer (ITS-2) from ribosomal DNA has been determined for 3 members of the Hypodontus macropi species complex. Sequences were compared from nematodes collected from 3 species of Australian macropodid marsupial, Petrogale persephone, Macropus robustus robustus and Thylogale billardierii. The ITS-2 of each operational taxonomic unit ranged from 287 to 292 bases in length, and had a GC content of 36.6-40.1%. Differences in nucleotide sequence between nematodes from the different host species ranged from 25.0% to 28.3%. The data suggest that H. macropi from P. persephone represents a different species to those in M. r. robustus and T. billardierii. The unique feature of this study is that it represents a comparison of the ribosomal DNA sequences of nematode species which are morphologically indistinguishable but which have been demonstrated to be genetically distinct (i.e. cryptic) species based on electrophoretic data. The results also demonstrate further that morphological characters alone are often not adequate for species recognition. Differences between these 3 species of H. macropi in their recognition sites for restriction endonucleases, indicates that a PCR-RFLP approach could be used, in conjunction with allozyme electrophoresis, to establish how many species are present within the H. macropi complex.
The free-living stages of gastro-intestinal nematodes on pasture (i.e. eggs, developing and infective larvae) are often overlooked and not considered by producers. The factors that influence the development, survival, distribution, or migratory behavior of the free-living larvae seen on pasture are primarily weather related. The deposition of helminth eggs in feces is the starting point for the contamination of the pasture and the subsequent development of the parasites. The cumulative numbers of eggs can be considerable by the end of the grazing season. Environmental factors will influence both development and survival of the larvae on pasture, as well as their distribution onto the herbage. Eggs deposited on the pasture will hatch and develop to the infective L3 stage. Under optimal conditions of moisture and temperature, larvae of Ostertagia ostertagi will reach the infective stage in approximately 5-6 days. Developmental time varies from one geographic region to another depending on prevailing weather. Eggs hatch and develop more slowly at lower temperatures. The rate of development increases to a maximum at higher temperatures after which development will be adversely affected and death of the larvae occurs. It is difficult to evaluate the effects of temperature without considering moisture. Moisture must be present to prevent desiccation and death of the developing larvae. Moisture has an effect on the movement and motility of the larvae. As the fecal pat dries out the larvae may desiccate and die. If the environment is dry, movement onto surrounding herbage would probably not be possible, thus forcing movement or migration into the soil beneath the fecal pat. Too much moisture (rain) may disrupt the pat, moving the larvae onto the surrounding herbage or carrying them away in the runoff. When moisture is adequate the movement of larvae on pasture may be affected by temperature. Temperature in the optimal range allows for larval activity and thus motility. Moisture provides a medium in which the larvae can move (there is probably little movement on dry surfaces). The effect of rainfall on dispersal of the larvae is important, a drop may transport larvae as far as 90 cm from the dung pat. However, optimal larval recovery is only approximately 5 cm (2-3 inch) from the edge of the fecal pat, with decreasing numbers out to approximately 25 cm. Several authors report larval migration into the soil as deep as 15 cm and as far as 40 cm from the center of the fecal pat. Soil type may have a major effect of the ability of larvae to migrate. The predilication of larvae to remain relatively close to the fecal pat may have substantial impact on transmission, as cattle do not graze close to fecal pats until forage is very limited. Therefore, intensive rotational grazing may enhance transmission by forcing animals to graze the highly contaminated areas. At the same time, intensive rotational grazing causes increased disruption of fecal pats, thus enhancing desiccation. Many investigators have utilized tracer calves grazing a pasture for a prescribed period of time to provide an indication of both species and numbers of worms present. Some investigators have used pasture larval counts, reporting number of larvae per kg of dry herbage and the genera present.
To establish which skin diseases occur in crocodiles, particularly those on farms, to indicate the relative frequency of each particular disease and to provide information on pathogenesis, especially in regard to lesions with two or more pathogens present.
A gross and microscopic retrospective (period of 1989 to 1995) and current (1996 to 1997) examination of skin lesions in crocodiles in Queensland and the Northern Territory.
Skin lesions were obtained from crocodiles on nine farms, from a group of experimental animals and from one adult found dead in the wild. A total of 203 lesions from 180, mostly young, crocodiles was examined; 119 lesions were from retrospectively examined cases and 84 were recent. The relative frequencies of four presumed primary pathogens in lesions were Dermatophilus sp 28.1%, fungi 14.8%, poxvirus 3.4% and probable Mycobacterium sp 2.5%. In addition, other bacteria of unknown significance were present in many lesions, and there was one case of presumed Paratrichosoma crocodilus infection. In 32.5% of lesions, multiple pathogens were identified.
Dermatophilosis is the most common and probably the most important skin disease of crocodiles in Australia, but it is frequently complicated by concurrent infection with fungi or other microorganisms.
The first description of the male and a redescription of the female of the nematode Paratrichosoma recurvum (Solger, 1877), a parasite of the abdominal skin of crocodiles, are presented on the basis of specimens collected from Crocodilus moreletii Duméril et Bibron from the Lagoon of Celestún, Yucatan, Mexico. The morphology of P. recurvum proved to be very similar to that of the only other congeneric species, P. crocodylus Ashford et Muller, 1978, but the former differed from the latter in having distinctly protruding polar plugs on eggs, reduced mesenchymal cells at the esophagointestinal junction, and a smooth spicular surface as well as in geographic distribution. The finding of P. recurvum in C. moreletii represents a new host record. Paratrichosoma spp. appear to be widely distributed in tropical countries of different continents and may be of economic importance for crocodile farms.
Oxidative stress has traditionally been viewed as a stochastic process of cell damage resulting from aerobic metabolism, and antioxidants have been viewed simply as free radical scavengers. Only recently has it been recognized that reactive oxygen species (ROS) are widely used as second messengers to propagate proinflammatory or growth-stimulatory signals. With this knowledge has come the corollary realization that oxidative stress and chronic inflammation are related, perhaps inseparable phenomena. New pharmacological strategies aimed at supplementing antioxidant defense systems while antagonizing redox-sensitive signal transduction may allow improved clinical management of chronic inflammatory or degenerative conditions, including Alzheimer's disease. Introduction of antioxidant therapies into mainstream medicine is possible and promising, but will require significant advances in basic cell biology, pharmacology, and clinical bioanalysis.
An examination of three specimens of the Morelet's crocodile, Crocodylus moreletii Duméril et Bibron, from the Lagoon of Celestún, Yucatan, Mexico revealed the presence of the following eight helminth species: Acanthostomum americanum (Pérez Vigueras, 1956), Pelaezia loossi (Pérez Vigueras, 1956), Telorchis sp. juv., Pseudoneodiplostomum groschafti sp. n. (all trematodes), Dujardinascaris helicina (Molin, 1860), Contracaecum sp. Type 2 larvae, Micropleura sp. and Paratrichosoma recurvum (Solger, 1877) (all nematodes). Pseudoneodiplostomum groschafti sp. n. is established by indication based on the description of specimens from Crocodylus rhombifer from Cuba, given by Groschaft and Barus (1970). Acanthostomum acuti Caballero et Brennes, 1959 is considered a synonym of A. americanum. A. americanum and D. helicina are recorded for the first time from Mexico and Micropleura sp. is the first American representative of the genus recorded outside South America. Findings of A. americanum, Telorchis sp., P. groschafti, D. helicina and Micropleura sp. in C. moreletii represent new host records. Some observations on the early development of D. helicina are provided. All species, except for P. recurvum, are briefly described and illustrated and some problems concerning their morphology, taxonomy and geographical distribution are discussed.
Using a molecular barcode, derived from single-specimen polymerase chain reaction (PCR) and sequencing of the 5' segment of the small subunit ribosomal RNA (SSU) gene, we have developed a molecular operational taxonomic unit (MOTU) scheme for soil nematodes. Individual specimens were considered to belong to the same MOTU when the sequenced segment of 450 bases was > 99.5% identical. A Scottish upland Agrostis-Festuca grassland soil was sampled, using both culture-based and random selection methods. One hundred and sixty-six cultured isolates were sequenced, and clustered into five MOTU. From 74 randomly sampled individuals across the study site, 19 MOTU were defined. A subsequent sample of 18 individuals from a single subplot contained eight MOTU, four of which were unique to the single subplot sample. Interestingly, seven of these MOTU were not present in the culture-independent sampling. Overall, a total of 23 MOTU were defined from only 240 sequences. Many MOTU could readily be assigned to classical, morphologically defined taxonomic units using a database of SSU sequences from named nematode species. The MOTU technique allows a rapid assessment of nematode taxon diversity in soils. Correlation with a database of sequences from known species offers a route to application of the technique in ecological surveys addressing biological as well as genetic diversity.
Suppressive anthelmintic treatment strategies originally designed to control Strongylus vulgaris in horses were extremely successful in reducing morbidity and mortality from parasitic disease. Unfortunately, this strategy has inadvertently resulted in the selection of drug-resistant cyathostomes (Cyathostominea), which are now considered the principal parasitic pathogens of horses. Resistance in the cyathostomes to benzimidazole drugs is highly prevalent throughout the world, and resistance to pyrantel appears to be increasingly common. However, there are still no reports of ivermectin resistance in nematode parasites of horses despite 20 years of use. It is unknown why resistance to ivermectin has not yet emerged, but considering that ivermectin is the single most commonly used anthelmintic in horses most parasitologists agree that resistance is inevitable. The fecal egg count reduction test is considered the gold standard for clinical diagnosis of anthelmintic resistance in horses, but diagnosis is complicated by lack of an accepted standard for the performance of this test or for the analysis and interpretation of data. Presently there is very little data available on the molecular mechanisms of anthelmintic resistance in cyathostomes; beta-tubulin gene is the only anthelmintic-resistance associated gene that has been cloned. The increasingly high prevalence of anthelmintic-resistant cyathostomes must be taken into account when designing worm control programs for horses. Strategies to decelerate further selection for drug resistance thereby extending the lifetime of currently effective anthelmintics should be implemented whenever possible. Considering the nature of the equine industry in which horses often graze shared pastures with horses from diverse locations, transmission and widespread dispersal of resistant parasites is virtually assured. A proactive approach to this problem centered on understanding the molecular basis of anthelmintic resistance in cyathostomes is required if we are to expect chemical control of nematodes in horses to remain a viable element of parasite control in the future.
Despite the fact that parasite dispersal is likely to be one of the most important processes influencing the dynamics and coevolution of host-parasite interactions, little information is available on the factors that affect it. In most cases, opportunities for parasite dispersal should be closely linked to host biology. Here we use microsatellite genetic markers to compare the population structure and dispersal of two host races of the seabird tick Ixodes uriae at the scale of the North Atlantic. Interestingly, tick populations showed high within-population genetic variation and relatively low population differentiation. However, gene flow at different spatial scales seemed to depend on the host species exploited. The black-legged kittiwake (Rissa tridactyla) had structured tick populations showing patterns of isolation by distance, whereas tick populations of the Atlantic puffin (Fratercula arctica) were only weakly structured at the largest scale considered. Host-dependent rates of tick dispersal between colonies will alter infestation probabilities and local dynamics and may thus modify the adaptation potential of ticks to local hosts. Moreover, as I. uriae is a vector of the Lyme disease agent Borrelia burgdorferi sensu lato in both hemispheres, the large-scale movements of birds and the subsequent dispersal of ticks will have important consequences for the dynamics and coevolutionary interactions of this microparasite with its different vertebrate and invertebrate hosts.
Considerable effort has been put into detecting and identifying parasitic nematodes in live ruminants, but to date most studies are limited to a small group of nematodes and/or to experimentally infected sheep. In this study, a PCR-based assay using species-specific primer pairs, located in the second internal transcribed spacer ribosomal DNA, was developed to identify nine different species from six different families of parasitic nematodes in a wild, unmanaged and naturally infected population of sheep. Each primer pair was tested for its specificity and sensitivity and it exclusively amplified the species it was designed for and exhibited a high degree of sensitivity. The method was applied to eggs and cultured larvae to identify the parasitic nematodes present in a pooled faecal sample from several host individuals with unknown parasite burden. To test detection reliability, a faecal sample from an individual with known parasite burden (through post-mortem analysis) was also examined. All species present could be correctly identified by PCR, but detecting very low levels and/or early stages of infection proved to be difficult. The method was also tested for its applicability to high through-put screening of faecal samples.
The crocodile project in Papua New Guinea Pathology of skin diseases in crocodiles
- M Laufa
- Buenviaje Gn
- Pw
- Martin
M, Laufa M (1982) The crocodile project in Papua New Guinea. Biol Conserv 22:169–179 Buenviaje GN, Ladds PW, Martin Y (1998) Pathology of skin diseases in crocodiles. Aust Vet J 76:357–363
Nematode-specific PCR primers for the 18S small subunit rRNA gene Hypobiosis in parasitic nematodes—an update
- Rogers Ad Rm
- Lambshead
- Pjd
- Smith
- Cr
RM, Rogers AD, Lambshead PJD, Smith CR (2005) Nematode-specific PCR primers for the 18S small subunit rRNA gene. Mol Ecol Notes 5:611–612 Gibbs HC (1986) Hypobiosis in parasitic nematodes—an update. Adv Parasitol 25:129–174
MRBAYES: Bayesian inference of phylogeny
- Jp
JP, Ronquist F (2001) MRBAYES: Bayesian inference of phylogeny. Bioinformatics 17:754–755
Seasonal trends in intestinal nematode infection and medicinal plant use among chimpanzees in the Mahale mountains, Tanzania Stress in farmed saltwater crocodiles (Crocodylus porosus): no difference between individually-and communally-housed animals
- Ma
- S Gotoh
- La Turner
MA, Gotoh S, Turner LA (1997) Seasonal trends in intestinal nematode infection and medicinal plant use among chimpanzees in the Mahale mountains, Tanzania. Primates 38:111–125 Isberg SR, Shilton CM (2013) Stress in farmed saltwater crocodiles (Crocodylus porosus): no difference between individually-and communally-housed animals. SpringerPlus 2:381
Is the population genetic structure of complex life cycle parasites determined by the geographic range of the most motile host? Tracking crocodile skin defects—from farm to product
- Kr
- Rellsta A C Karvonen
- Jokela
KR, Karvonen A, Rellsta C, Jokela J (2010) Is the population genetic structure of complex life cycle parasites determined by the geographic range of the most motile host? Infect Genet Evol 10: 1271–1277 Manolis SC, Webb GJW (2011) Tracking crocodile skin defects—from farm to product. Rural Industries Research and Development Corporation: Canberra. Publication No. 11/012
Seasonal variation of Opisthorchis viverrine infection in cyprinoid fish in north-east Thailand: implications for parasite control and food safety Redescription of two trichurid nematode parasites of vertebrates in Australia and Papua New Guinea Environmental factors influencing transmission
- P V Pipitgool
- Elkins T Db Srisawangwong
- Mr
P, Pipitgool V, Srisawangwong T, Elkins DB, Haswell-Elkins MR (1997) Seasonal variation of Opisthorchis viverrine infection in cyprinoid fish in north-east Thailand: implications for parasite control and food safety. Bull World Health Organ 75:125–131 Spratt DM (1985) Redescription of two trichurid nematode parasites of vertebrates in Australia and Papua New Guinea. Trans R Soc S Aust 109:143–150 Stromberg BE (1997) Environmental factors influencing transmission. Vet Parasitol 72:247–262
Tracking crocodile skin defects-from farm to product. Rural Industries Research and Development Corporation: Canberra
- S C Manolis
- Gjw Webb
Manolis SC, Webb GJW (2011) Tracking crocodile skin defects-from
farm to product. Rural Industries Research and Development
Corporation: Canberra. Publication No. 11/012
Redescription of two trichurid nematode parasites of vertebrates in Australia and Papua New Guinea
- D M Spratt
- DM Spratt
Spratt DM (1985) Redescription of two trichurid nematode parasites of
vertebrates in Australia and Papua New Guinea. Trans R Soc S Aust
109:143-150