Population genetic structure of Ascaridia galli re-emerging in non-caged laying hens

Section for Parasitology, Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, P.O. 7028, Uppsala SE-750 07, Sweden.
Parasites & Vectors (Impact Factor: 3.43). 05/2012; 5(1):97. DOI: 10.1186/1756-3305-5-97
Source: PubMed


The poultry roundworm Ascaridia galli has reappeared in hens kept for egg production in Sweden after having been almost absent a decade ago. Today this is a frequent intestinal nematode parasite in non-caged laying hens. The aim of this study was to investigate the genetic diversity (Fst) in A. galli collected from different poultry production sites in southern Sweden, to identify possible common routes of colonization.
Adult parasites (n = 153) from 10 farms, including both broiler breeder parents and laying hens, were investigated by amplified restriction fragment length polymorphism analysis (AFLP). Worms from a Danish laying hen farm were also included for comparison. Most of the farms were represented by worms from a single host, but on two farms multiple samples from different hosts were assessed in order to study flock variation.
A total of 97 fragments (loci) were amplified among which 81% were variable alleles. The average genetic diversity was 0.13 (range = 0.09-0.38), which is comparable to other AFLP studies on nematodes of human and veterinary importance. Within-farm variation showed that worms harboured by a single hen in a flock covered most of the A. galli genetic variation within the same flock (Fst = 0.01 and 0.03 for two farms). Between-farm analysis showed a moderate population genetic structure (Fst = 0.13), along with a low mutational rate but high gene flow between different farms, and absence of strong genetic selection. Network analysis showed repeated genetic patterns among the farms, with most worms on each farm clustering together as supported by high re-allocation rates.
The investigated A. galli populations were not strongly differentiated, indicating that they have undergone a genetic bottlenecking and subsequent drift. This supports the view that the investigated farms have been recently colonized, and that new flocks are reinfected upon arrival with a stationary infection.

Download full-text


Available from: Johan Höglund
  • Source
    • "The Min River valley and the existence of six relatively isolated mountain ranges that giant panda inhabit, three of which were sampled in this study, might result in a distinct population structure among the populations. Second, unlike most free-living organisms, not only the parasites own reproductive and transmission patterns but also the genetics and behavior of the host could influence their genomic variation [31]. Host movement is an important determinant of population genetic structure in parasitic nematodes, and the frequent gene flow and weak population subdivisions will result from mobile vertebrate hosts [32]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Baylisascaris schroederi is one of the most common nematodes of the giant panda, and can cause severe baylisascarosis in both wild and captive giant pandas. Previous studies of the giant pandas indicated that this population is genetically distinct, implying the presence of a new subspecies. Based on the co-evolution between the parasite and the host, the aim of this study was to investigate the genetic differentiation in the B. schroederi population collected from giant pandas inhabiting different mountain ranges, and further to identify whether the evolution of this parasite correlates with the evolution of giant pandas. In this study, 48 B. schroederi were collected from 28 wild giant pandas inhabiting the Qinling, Minshan and Qionglai mountain ranges in China. The complete sequence of the mitochondrial cytochrome b (mtCytb) gene was amplified by PCR, and the corresponding population genetic diversity of the three mountain populations was determined. In addition, we discussed the evolutionary relationship between B. schroederi and its host giant panda. For the DNA dataset, insignificant Fst values and a significant, high level of gene flow were detected among the three mountain populations of B. schroederi, and high genetic variation within populations and a low genetic distance were observed. Both phylogenetic analyses and network mapping of the 16 haplotypes revealed a dispersed pattern and an absence of branches strictly corresponding to the three mountain range sampling sites. Neutrality tests and mismatch analysis indicated that B. schroederi experienced a population expansion in the past. Taken together, the dispersed haplotype map, extremely high gene flow among the three populations of B. schroederi, low genetic structure and rapid evolutionary rate suggest that the B. schroederi populations did not follow a pattern of isolation by distance, indicating the existence of physical connections before these populations became geographically separated.
    Full-text · Article · Aug 2013 · Parasites & Vectors
  • Source
    • "When our C. oncophora isolates were analysed with AFLP, we found no evidence of genetic bottlenecking in either of the drug-selected worms, and by comparing their genetic makeup pre- and post-treatment. In veterinary parasitology, AFLP has previously been used mainly to compare the genetic structures of various parasitic nematodes of livestock with different geographic backgrounds (Höglund et al. 2012, 2006; Nejsum et al. 2005; Troell et al. 2006), but also to compare consecutive stages of increased benzimidazole- and levamisole-resistant isolates during selection (Otsen et al. 2001). Höglund et al. (2006) concluded that most nematodes of domesticated hosts usually have very little genetic difference between populations, and are characterised by strong gene flow and expanding populations. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this study was to investigate genetic selection and P-glycoprotein (PGP) expression in three different isolates of Cooperia oncophora before treatment and after ivermectin (IVM) injection. Adult parasites were recovered from nine calves experimentally infected with the isolates represented by one IVM susceptible laboratory isolate, and two field isolates showing signs of phenotypic macrocyclic lactone resilience according to the faecal egg count reduction test. Five males and five females per isolate were examined both pre- and post-IVM treatment giving a total of 60 worms. A sequence from C. oncophora (Con-pgp) was identified, showing 83 % similarity to Pgp-9 of Caenorhabditis elegans. Primers specific to putative Con-pgp-9 mRNA were designed, generating a 153-bp PCR product. Total RNA was prepared from all worms, and Con-pgp-9 expression was measured by quantitative real-time reverse transcription PCR. Our results showed that mean PGP concentrations were four to five times higher in female as compared to male worms. No significant differences in gene expression between experimental groups pre- and post-IVM selection were detected. However, PGP gene expression tended to be increased by IVM treatment in male worms (p = 0.091), with 70 % higher mean expression in treated than in untreated male worms. Amplified fragment length polymorphism analysis did not demonstrate any bottleneck effect within the different isolates post-treatment. The total mean gene diversity values were 0.158 and 0.153 before and after treatment, respectively. Inbreeding coefficient in subpopulations compared to total population F ST was 0.0112, suggesting no genetic differentiation between or within the investigated isolates in relation to treatment. In conclusion, comparison of Con-pgp-9 expression showed no significant difference before and after treatment, but some tendency towards increasing expression in male worms.
    Full-text · Article · Jun 2013 · Parasitology Research
  • Source
    • "The low heterozygosity within isolates of P. equorum indicates the relative lack of genetic variation among the worms both at a global and at a national scale. Furthermore, the value for total genetic diversity (Ht) across all global isolates and among the Swedish isolates was also relatively low, respectively Ht = 0.10 and Ht = 0.09, as it also was for A. suum (Ht = 0.20) (Nejsum et al., 2005) and A. galli (Ht = 0.15) (Höglund et al., 2012). This information suggests that low genetic diversity is a general feature of ascaroid nematodes. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The large roundworm of horses, Parascaris equorum is considered ubiquitous in breeding operations, and is regarded as a most important helminth pathogen of foals. Over the past decade, this parasite has been reported increasingly resistant to anthelmintic drugs worldwide. This paper reports analysis of the population genetic structure of P. equorum. Adult parasites (n = 194) collected from Sweden, Norway, Iceland, Germany, Brazil and the USA were investigated by amplified restriction fragment length polymorphism (AFLP) analysis. The genetic variation was low (Hj =0.12-0.4), for the global population of worms. This was accompanied by a weak degree of population structure (Fst = 0.2), low gene flow (Nm = 1.0) and low mutation rate (4 Nμ = 0.07). Thus, the low genetic diversity is probably a result of a low mutation rate in DNA, although the gene flow (due to global movement of horses) is large enough to allow the spread of novel mutations. Surprisingly, isolates from Icelandic horses were not found to be different from other isolates, in spite of the fact that these have been isolated for thousands of years. The study indicates that the global P. equorum population is essentially homogenous, and continents do not appear to be strong barriers for the population structure of this species. Consequently, the potential spread of rare anthelmintic resistance genes may be rapid in a homogenous population.
    Full-text · Article · Nov 2012 · Infection, genetics and evolution: journal of molecular epidemiology and evolutionary genetics in infectious diseases
Show more

Similar Publications