Detection of Leishmania spp. Infection by Immunohistochemistry in Archived Biopsy Samples from Dogs with Colitis in an Area Endemic for Leishmaniosis

Previous studies have demonstrated the presence of Leishmania infantum amastigotes in the colonic mucosa of seropositive sick dogs. However, there are no studies that have investigated the presence of L. infantum infection in dogs diagnosed with inflammatory bowel disease (IBD). The aims of this study were: (1) to investigate retrospectively the presence of Leishmania spp. antigen by immunohistochemistry (IHC) in biopsy samples taken from the colon of dogs with IBD in an area endemic for leishmaniosis, and (2) to describe the main histopathological findings in these cases. Clinicopathological data and histopathological results were reviewed from 106 cases of canine colitis. IHC to detect Leishmania spp. antigen had been performed at the time of diagnosis in 13 cases and we performed IHC in 56 more cases. Five of the 69 cases (7.2%) were positive for Leishmania spp. antigen by IHC. Two positive biopsy samples had histiocytic inflammation and three had lymphoplasmacytic inflammation. The number of amastigotes was variable and independent of the type and grade of inflammatory infiltrate. The results suggest that Leishmania spp. infection is associated with chronic colitis in areas endemic for the infection. Therefore, Leishmania IHC should be used routinely as a diagnostic tool when evaluating colonic biopsy samples from dogs in endemic areas, to exclude or confirm an infection by this parasite in dogs with chronic colitis.