Parasitic gastroenteritis (PGE) due to nematode infections is a major constraint on small ruminant production worldwide.
In temperate areas, sheep and goats are infected with a range of worm species, with the most prevalent species being Teladorsagia circumcincta. This pathogenic nematode is very similar to O. ostertagi in terms of its host niche and life cycle.
All grazing sheep are exposed to helminths at pasture and intensification of grazing systems increases the risk of disease.
Estimates of the annual cost of sheep nematodes to the UK industry alone are in the region of €99M. These costs are likely to be underestimates of the true financial impact of infection.
There is widespread anthelmintic resistance in this worm species, including multi-drug class resistance, making alternative control strategies such as vaccination a real necessity.