Investigating the gut parasite Eimeria in UK sheep: parasite species diversity and impacts on the gut microbiome

Food producing animals are infected by many parasite species, which severely compromise their health and productivity. Eimeria parasites are single-celled pathogens which are very common infections of farmed animals in the UK and worldwide. They can cause gut disease (called coccidiosis) in young animals including sheep, cattle and poultry, leading to diarrhoea, reduced weight gains and even death. Although Eimeria parasites are well-studied in poultry and commercial vaccines are available to control coccidiosis in chickens, research in sheep is much more limited and there are no vaccines. Control in sheep relies on good animal husbandry and use of drugs. However, there are reports of resistance to one drug, toltrazuril, which is often used to control coccidiosis in sheep, posing a threat to sustainable control. A number of different Eimeria species infect sheep and some are described as more likely to cause disease than others. Distinguishing between Eimeria species is usually done by microscopy, looking at the shape and size of Eimeria oocysts (eggs). However, this is not a reliable method of detecting different Eimeria species, particularly if sheep are infected by more than one species. DNA-based methods to distinguish between Eimeria species have been developed but have not been widely applied in the UK and elsewhere. Another area where further research is needed, is understanding how Eimeria infections impact on the gut microbiome of sheep. It is known that the microecology of the gut plays a critical role in animal health and that Eimeria infections cause disturbances (dysbiosis) in the gut microbial community of poultry but this has not been to date explored in sheep.