Diagnosis of triclabendazole resistance in Fasciola hepatica
- Neil Sargison, BA, VetMB, PhD, DSHP, DipECSRHM, FRCVS
- Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Veterinary Centre, Roslin, Midlothian EH25 9RG, UK
Fasciola hepatica has enormous biotic potential, involving sexual, hermaphroditic, or parthenogenic reproduction in the final mammalian host and clonal asexual multiplication in intermediate molluscan hosts. Helminth parasites typically have large genomes with high levels of genetic polymorphism, and the existence of triploidy in some populations of F hepatica confers an even greater potential for genetic variation (Fletcher and others 2004). These factors have enabled the evolution of complex life cycles that are dependent on overlap of suitable environments for free-living stages, intermediate and final hosts, while also conferring the ability to quickly take advantage of favourable opportunities afforded by relatively short-term animal and pasture management changes and effects of micro- and macro-climatic variation on their biotopes. The same evolutionary potential inevitably enables populations of these parasites to survive despite a variety of unfavourable conditions, such as exposure to fasciolicidal anthelmintics. The diagnosis and investigation of fasciolosis is a prerequisite for understanding, predicting and managing changing disease patterns resulting from evolving epidemiological trends and the emergence of anthelmintic resistance. Such investigations depend on the application of a combinations of diagnostic methods such as: postmortem identification of the parasites and/or characteristic pathology; results of clinical examination; clinical biochemistry; detection of antibodies against components of F hepatica or of F hepatica gut antigens in host faeces; faecal examination for F hepatica eggs; and the application of molecular biological tools (Martinez-Perez and others 2012).
Various anthelmintics are licensed for use against F hepatica in cattle and sheep. All are effective against adult flukes in the bile ducts, but differ in their efficacy against immature flukes in the liver parenchyma. The wide spectrum …