Population genetics and genomics of ovine nematode parasites and their application to study the molecular basis of anthelmintic resistance

Lead Research Organisation: Moredun Research Institute
Department Name: Vaccines and Diagnostics


Parasitic worms (nematodes) represent one of the most serious health problems of grazing livestock (sheep, cattle and goats) in the UK and throughout the world, causing significant economic loss and animal welfare problems. The most important types of parasitic worms live in the stomach and intestine of their animal host. Some cause diarrhoea, which can be severe, whilst others feed on blood and cause internal bleeding and anaemia. Severely affected animals may die, or have to be destroyed on welfare grounds, whilst more mildly affected animals have sub-optimal growth rates which can have serious economic implications for the farmer. Indeed, parasitic worms the most economically important disease of sheep and have been estimated to cost the sheep industry in the region of £80M per annum. They are similarly important in cattle. These economic losses are directly related to the severity of infection and so by reducing the number of parasites infecting livestock, we can proportionally reduce the costs to the industry as well as improving animal welfare. Control of these parasites is heavily dependent upon the routine treatment of livestock with drugs (anthelmintics, commonly called wormers) and there are only three major types available. In many parts of the world, parasitic worms are now resistant to all of these drugs. In the UK, over 60% of sheep worms are resistant to at least one drug class and multiple resistance is increasing. Consequently, the problem of drug resistant worms is a significant threat to the sustainability of the UK sheep and cattle industries. Detection of resistance is problematic and current methods are old fashioned, labour-intensive and very insensitive, making diagnosis unreliable and early detection impossible. Consequently, there is a need to develop modern sensitive tests for routine diagnosis and surveillance and as tools to study the way in which drug resistant parasites appear and spread. An understanding of these issues is critical for the design of parasite control regimes that are both effective and sustainable and to develop ways of using these important drugs that do not exacerbate the development of resistance This project aims to develop and apply tools to elucidate a number of key aspects of the biology and genetics of these parasites that will help us understand how drug resistance develops and how it may be combated. Sheep worms will be studied because drug resistance is the most advanced in these parasites and they are amenable to experimental work. The project will also develop a genome sequence database that will not only enable us to study the problem of resistance but will assist other researchers to develop vaccines and identify new drug targets in these parasites. The research team will be multidisciplinary and include vets and scientists with expertise in genetics, molecular biology, genomics, epidemiology, statistics, parasitology and clinical veterinary medicine. The first stage of the project will be to establish the tools needed, including DNA sequence and genetic markers from the two major parasite species of parasite to be studied. In parallel to this work, parasite samples will be collected from sheep throughout the UK and molecular-based diagnostic tests used to determine the species present. The genetic markers that have been developed will then be used to 'fingerprint' the parasite populations to investigate their genetic diversity. Parasite genes that are already known to confer resistance will be sequenced to investigate the different ways parasites are becoming resistant to these drugs and to provide information that will pave the way for the development sensitive diagnostic tests based on parasite DNA typing. Finally, a system of genetic analysis, not previously applied to parasitic worms, will be investigated that will scan the worm's genome to identify regions containing previously unknown resistance-conferring genes.

Technical Summary

Parasitic nematodes represent one of the most serious animal health problems of UK livestock causing significant economic loss and animal welfare problems. There has been remarkably little application of modern molecular epidemiology and population genetics to study parasitic nematodes and yet such information is needed to underpin control strategies using vaccines, anthelmintics or host resistance. Control of these parasites is dependent upon the routine use of anthelmintics and resistance problems are a major problem in sheep and an emerging problem in cattle. This project will focus on two important ovine nematodes, Haemonchus contortus and Teladorsagia circumcincta with aim of developing and using new tools to investigate their population structure and approaches to study the genetics of anthelmintic resistance. The key aims are: (1) To develop genetic, biological and genomic resources for these parasites to allow population genetic analysis and the study the molecular genetics of anthelmintic resistance; (2) To define the distribution of nematode parasite species in the UK and provide an broad definition of nematode diversity throughout the UK; (3) Investigate the population structure, and cryptic speciation on selected farms in more detail (4) Analyse the population genetics of benzimidazole resistance (as a model for anthelmintic resistance in general) to investigate the validity of candidate resistance gene studies and how resistance alleles arise and spread in parasite populations;(5) Undertake a genome-wide approach for H.contortus, utilising a panel of 100-200 microsatellite loci to identify loci under selection by ivermectin treatment. The results and resources generated by this project will provide the basis for future control strategies and the conceptual framework and reagents for developing markers for anthelmintic resistance and investigating the role of parasite diversity in vaccine development and breeding for host resistance. .


10 25 50