Asymptomatic colitis in naturally infected dogs with Leishmania infantum: a prospective study.

A total of 31 dogs with naturally occurring and symptomatic leishmaniasis (Leishmania infantum), but without historical or clinical evidence of overt colitis, were included in this study. With owners' consent, a colonoscopy was performed in all these dogs, revealing patches of hyperemic, edematous, irregular, and mildly erosive colonic mucosa in 25.8% of the animals. Biopsies were obtained from the colonic mucosa and stained with hematoxylin-eosin (histopathology) and avidin-biotin-peroxidase technique (immunohistochemical detection of parasites). Leishmania amastigotes were detected immunohistochemically in 32.3% of the dogs. The most common inflammatory pattern in the colonic mucosa of these dogs was pyogranulomatous (90%), whereas in the dogs without Leishmania amastigotes immunohistochemically detected in the colonic mucosa (67.7%), there was no evidence of gross and microscopic lesions. Also, in 2 of the 10 dogs in which parasites were detected immunohistochemically in the colonic mucosa, no lesions could be detected on colonoscopy. There was no correlation between the dogs with or without parasites detected in the colonic mucosa regarding the sex, age, or the type of diet of these animals. However, the positive correlation (P < 0.001) found between colonic parasitism and gross lesions detected on colonoscopy would justify the inclusion of canine leishmaniasis in the list of differentials of canine chronic or recurrent colitis.