Mycobacterium genavense Infection as a Cause of Disseminated Granulomatous Inflammation in a Horse

•Yearling mare presented with respiratory symptoms resistant to therapy.•Postmortem examination revealed disseminated granulomatous inflammation.•Infection with Mycobacterium genavense diagnosed by polymerase chain reaction.

A yearling mare (16-month-old) presented with respiratory symptoms and a history of retarded physical development for several weeks. Clinical and laboratory examinations indicated infectious disease. Attempts of antibiotic therapy failed, and the animal was continuously in poor general condition, so it was euthanized due to bad prognosis. Necropsy and microscopical examinations revealed granulomatous inflammation in the spleen, lungs, aortic wall, aortic, mandibular, and inguinal lymph nodes. Intracellular acid-fast bacilli were solely detectable in the spleen, but only in very few numbers. Molecular biological investigations of formalin-fixed tissue samples showed the presence of Mycobacterium genavense DNA in the spleen and the aortic wall. To the best of our knowledge, this is the first report on M. genavense infection in a horse.