Intestinal histoplasmosis with granulomatous colonic and mesenteric lymphadenitis due to Histoplasma mississippiense infection in an American Mammoth Jackstock donkey (Equus asinus)

Abstract

Histoplasmosis is a rarely reported clinical disease of equids in North America and is historically attributed to Histoplasma capsulatum var. capsulatum. This report details a case of intestinal histoplasmosis with lymphadenitis in an American Mammoth Jackstock donkey from Mississippi. Clinically, the donkey had chronic wasting, poor appetite, diarrhoea and an intra-abdominal mass detected by ultrasound. Grossly, the distal small and proximal large intestines contained multifocal, raised, tan, nodular, button ulcers along the mucosal surface. The associated colonic and mesenteric lymph nodes were severely enlarged, mottled tan to red and firm, and formed a large multinodular mass within the mesentery. Microscopically, lesions consisted of nodular infiltrates of epithelioid macrophages and multinucleated giant cells laden with numerous yeasts, along with mucosal ulceration and necrosis. Fungal polymerase chain reaction from lesioned intestines and lymph nodes targeting the internal transcribed spacer region yielded a 585 bp sequence that matched identically to two human isolates of Histoplasma mississippiense, one of several cryptic species previously classified together as H. capsulatum var. capsulatum endemic to North America. This case represents the first molecular identification of a Histoplasma species infecting a North American equid and the second report of histoplasmosis in a donkey from North America.