Canine Histoplasmosis in Japan

Histoplasmosis is a fungal infection caused by Histoplasma capsulatum and is distributed a worldwide. Although the disease has been treated as an imported mycosis, some autochthonous human, 1 equine and 4 canine cases suggested that the disease is endemic. Histoplasmosis is classified depending on the variety of causative agent. Histoplasmosis farciminosi known as pseudofarcy, is manifested only in Perissodactyla where it invades lymph nodes and lymph ducts, and is recognized by isolation from horses. Historically, Japan was one of the endemic areas of pseudofarcy before World War II, and more than 20,000 cases were recorded in horses used by the military. Interestingly, Japanese canine histoplasmosis uniformly showed skin ulcers and granulomatous lesions on the skin without pulmonary or gastrointestinal involvement, both of which were very similar to pseudofarcy. It was diagnosed as histoplasmosis by the detection of internal transcribed spacer legions of rRNA gene of H. capsulatum from paraffin embedded tissue samples. Furthermore, the fungal isolate from the human case with no history of going abroad or immigrating was identified as H. capsulatum var. farciminosum by a gene sequence. These facts indicated that pseudofarcy is not only an infectious disease in horses, but also a zoonotic fungal infection. Japanese autochthonous canine histoplasmosis might be a heteroecism of pseudofarcy because of its likeness to the human case, the similarity of clinical manifestations and the historical background at this stage.