Discussion

Fasciola hepatica is recognised as a parasite affecting grazing animals, and reports of clinically affected horses appear in the literature. Our study, which was funded by the Animal Welfare Foundation, aimed to establish the extent of the problem, to assist with diagnosis and ultimately to improve the welfare of horses. Firstly, we undertook a prevalence survey in abattoir horses, with F. hepatica infection status determined by both liver inspection and excretory-secretory antibody ELISA. Of 342 horses examined, four (1.1%) were positive for adult flukes in the liver, whilst 26 (7.6%) tested positive on ELISA. Secondly, we conducted a case control study of horses with and without liver disease from the UK horse population, to determine whether F. hepatica was a cause of liver disease in horses.  Of 277 horses recruited into the study, 17 (6.1%) tested positive for liver fluke on ELISA. Horses with liver disease were significantly more likely to test positive for liver fluke than controls. Thirdly, using flukes (n=123) collected from horses at abattoir, we performed microsatellite analysis. This showed that these flukes were likely to have come from the same population as flukes derived from cattle and sheep. Our results show that F. hepatica is causing clinically important morbidity in horses, and should be considered as a differential diagnosis in cases of liver disease in at-risk horses.