title: Fasciola hepatica demonstrates high levels of genetic diversity, a lack of population structure and high gene flow: possible implications for drug resistance.
abstract: Fasciola hepatica, the liver fluke, is a trematode parasite of considerable economic importance to the livestock industry and is a re-emerging zoonosis that poses a risk to human health in F. hepatica-endemic areas worldwide. Drug resistance is a substantial threat to the current and future control of F. hepatica, yet little is known about how the biology of the parasite influences the development and spread of resistance. Given that F. hepatica can self-fertilise and therefore inbreed, there is the potential for greater population differentiation and an increased likelihood of recessive alleles, such as drug resistance genes, coming together. This could be compounded by clonal expansion within the snail intermediate host and aggregation of parasites of the same genotype on pasture. Alternatively, widespread movement of animals that typically occurs in the UK could promote high levels of gene flow and prevent population differentiation. We identified clonal parasites with identical multilocus genotypes in 61% of hosts. Despite this, 84% of 1579 adult parasites had unique multilocus genotypes, which supports high levels of genotypic diversity within F. hepatica populations. Our analyses indicate a selfing rate no greater than 2%, suggesting that this diversity is in part due to the propensity for F. hepatica to cross-fertilise. Finally, although we identified high genetic diversity within a given host, there was little evidence for differentiation between populations from different hosts, indicating a single panmictic population. This implies that, once those emerge, anthelmintic resistance genes have the potential to spread rapidly through liver fluke populations.
authors.affiliation: Veterinary Parasitology, Institute of Infection and Global Health, University of Liverpool, Liverpool L3 5RF, UK. Electronic address: nbeesley@liverpool.ac.uk.
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Beesley
authors.affiliation: Veterinary Parasitology, Institute of Infection and Global Health, University of Liverpool, Liverpool L3 5RF, UK.
authors.forename: Diana J L
authors.initials: DJ
authors.lastname: Williams
authors.affiliation: Centre for Genomic Research, Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK.
authors.forename: Steve
authors.initials: S
authors.lastname: Paterson
authors.affiliation: Veterinary Parasitology, Institute of Infection and Global Health, University of Liverpool, Liverpool L3 5RF, UK.
authors.forename: Jane
authors.initials: J
authors.lastname: Hodgkinson
mesh_terms: D000483:Alleles; D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy / Q000453:epidemiology / Q000469:parasitology; D004272:DNA, Mitochondrial / Q000235:genetics; D004351:Drug Resistance / Q000235:genetics; D005210:Fasciola hepatica / Q000187:drug effects* / Q000235:genetics*; D005211:Fascioliasis / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary; D005260:Female; D051456:Gene Flow; D017238:Genes, Helminth; D056426:Genetic Loci; D014644:Genetic Variation; D005828:Genetics, Population; D049751:Genome, Helminth; D006790:Host-Parasite Interactions; D008297:Male; D018895:Microsatellite Repeats; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy / Q000453:epidemiology / Q000469:parasitology; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D000871:Anthelmintics; D004272:DNA, Mitochondrial
keywords: Anthelmintic resistance; Diversity; Fasciola hepatica; Gene flow; Microsatellites; Population genetics; Self-fertilisation