Facing the threat of equine parasitic disease.

Horses worldwide are exposed to a complex mixture of intestinal parasitic helminths. When burdens are high, these parasites can seriously compromise health and welfare. Some helminth species have an extremely high prevalence and are difficult to control, not least because there is a limited understanding of their most basic biology. Furthermore, levels of resistance to some of the commonly used anthelmintics are widespread and increasing. The cyathostomins are the most common nematode species affecting equids worldwide. Within this group of parasites are more than 50 different species. Until recent research activities, little was known about the contribution that individual species make to clinical disease, parasite epidemiology and anthelmintic resistance. This review describes some of the recent research advances in the understanding of cyathostomins in these areas. As part of the research effort, molecular tools were developed to facilitate identification of the non-parasitic stages of cyathostomins. These tools have proved invaluable in the investigation of the relative contributions that individual species make to the pathology and epidemiology of mixed infections. At the more applied level, research has also progressed in the development of a diagnostic test that will allow numbers of cyathostomin encysted larvae to be estimated. This test utilises cyathostomin-specific serum antibody responses as markers of infection. As anthelmintic resistance will be the major constraint on parasite control in future, researchers are actively investigating mechanisms of drug resistance and how to improve the detection of resistance in the field. Recent developments in these areas are also outlined.