Characterisation of IgE antibody responses to Anoplocephala perfoliata

Abstract

Between April 2006 and September 2007, ceco-colic intussusceptions were diagnosed in four standardbred horses aged 1-3 years on a well-managed farm in southern Ontario, Canada. Throughout this period there were approximately 90 standardbred horses maintained on the farm. Surgery on all four horses with ceco-colic intussusceptions revealed the presence of large numbers of Anoplocephala perfoliata in all four animals. Blood samples were collected from all horses on the farm in October 2007 and examined for antibody to a 12/13 kDa A. perfoliata secretory protein [1,2]; 61 of 67 (91%) horses were seropositive and themean optical density (OD) of all horses was 1.391 (median 1⁄4 1.538). Among the seropositive horses, 4 (6% of total) and 57 (85% of total) had OD values indicative of moderate (0.201-0.600) and high (>0.600) infection intensity, respectively. This is in contrast to a 2003-2004 study of 234 horses in southern Ontario of multiple breeds, 117with colic and 117 controls; 131 (56%) were seropositive to A. perfoliata and the mean OD of all horses was 0.509 (median 1⁄4 0.243). Among the seropositives, 65 (27.9% of total) and 66 (28.1% of total) had OD values indicative of moderate and high infection intensity, respectively. Assuming data independence, horses on the standardbred farm were significantly more likely to be seropositive than the 2003-2004 reference population (odds ratio 1⁄4 8.0; 95% CI 1⁄4 3.3-19.6; p < 0.0001). The reason for the high prevalence and high intensity of A. perfoliata infection among horses on the standardbred farm are unclear. In November each year, for multiple years, all yearlings and adult horses on the farm were treated for tapeworms with double-dose pyrantel. In contrast, only 23% of the reference population had received treatment with a cestocide in the year prior to sampling. Since neither underdosing nor use of outdated product appear to have been a concern, it is possible that the problemwas associatedwith resistance to pyrantel in A. perfoliata. However, because of the lack of a sensitive diagnostic method for current infection, this was not possible to prove.