Comparison of three methods for the diagnosis of Oxyuris equi infection in horses

Background: Horses are parasitised by several intestinal helminths such as strongyles, ascarids, tapeworms and pinworms. Oxyuris equi, the horse pinworm, causes perineal irritation (tail rubbing, broken hairs and excoriated skin) [1]. Faecal Egg Count is the routine method for the diagnosis of intestinal parasite in equids [2]; however, pinworm eggs are rarely observed in faecal samples because O. equi females deposit eggs in the perianal region [1]. Objectives: The aim of this study was to compare three diagnostic techniques namely Mini-FLOTAC, Proudman test and Scotch test for detecting O. equi eggs. Study design: Assay comparison. Methods: Scotch test, Mini-Flotac technique and Proudman test were performed on 2,857 horses to determine technique diagnostic accuracy. Two Scotch tests were performed for each horse and faeces were collected directly from the rectum. The faecal samples were analysed in duplicate using both Mini-FLOTAC and Proudman test with a Sheather's saturated sugar solution. Considering all three methods used, a total of 17,142 assays was performed. Results: Overall, O. equi eggs were found in 125 (4.4%) horses. Of these 91 (72.8%) were positive only by Scotch test; 19 (15.2%) by Scotch test and Mini-Flotac; 5 (4.0%) by Scotch test and Proudman test; 7 (5.6%) only by Mini-Flotac and 3 (2.4%) only by Proudman test. Main limitations: Underestimation of O. equi prevalence due to the egg laying pattern. Conclusions: The number of horses positive for O. equi eggs was higher using the Scotch test, thus showing that it is a more sensitive method for diagnosis of pinworms than FEC and Proudman test.