Histoplasmosis in the lung of a race horse with yersiniosis

A 4-year-old female thoroughbred race horse died of acute peritonitis cause d by necrotizing granulomatous duodenitis. Yersinia enterocolitica was immi mohistochemically demonstrated in macrophages in granulomas developed in th e duodenum, lung, liver and abdominal lymph nodes. The yeast-like fungi wer e found in the cytoplasmic vacuoles of macrophages in the lung that infiltr ated into the granulomas and surrounding alveoli with congestive edema. The yeast-like fungi were positively stained by Gomori-Grocott chromic acid me thenamine silver stain and immuno-histochemically stained with anti-histopl asma antibody. In this case, it was considered that granulomas formed in th e duodenum, lung, liver and abdominal lymph nodes were primarily caused by Yersinia enterocolitica due to idiopathic weakening of the immune system. Y east-like fungi immunohistochemically identified as histoplasmas secondaril y infected the lung. This is the first case regarded as equine histoplasmos is capsulati in Japan.