Klossiella equi, an underreported parasite of equids in the Americas.

Klossiella equi Baumann, 1946 (Apicomplexa: Coccidia) is a globally distributed adeleorinid parasite that infects the kidneys of equid hosts. Considered an uncommon parasite, when K. equi is detected, it is typically an incidental finding during histologic examination of the kidneys as part of routine necropsy. In the present study, kidney was collected opportunistically from 3 different equine populations: 1) routine necropsies at the Ontario Veterinary College (OVC; n = 48); 2) natural mortalities from the Sable Island wild horse herd (n = 25); and 3) routine necropsies of animals from University of Kentucky parasitological research herds (mares n = 3, foals n = 16). A Polymerase Chain Reaction-based method targeting a 575 base pair region of the K. equi mitochondrial genome was developed and applied to DNA extracted from kidney to detect K. equi infections. Overall prevalence was 45% (41/92); no animal < 10 months-of-age was infected. Among animals ≥ 1 year-of-age, prevalence was 58% (40/67) and high at all locations: OVC prevalence of 50% (24/48); Sable Island prevalence of 56% (14/25); and 100% of the mares (3/3) from Kentucky were infected. Twenty of the K. equi-positive cases necropsied at OVC also had routine histological evaluation that failed to detect any K. equi infections. A DNA sample from sporocysts shed in urine by an Argentinian horse was used for sequenced-based genotyping; the resulting sequence matched the K. equi reference (MH203050) at 100% over 957 base pairs. These data confirm that K. equi is grossly underreported and histological evaluation is an insensitive method of detection.