Histoplasmosis in the skin and gingiva in a dog

An 8-year-old, female mongrel dog had granulomatous lesions in the skull skin and gingiva of the left mandible. The lesions were macroscopically seen as grayish white papular granulomas, and microscopically consisted to numerous swollen macrophages and a few neutrophils without fibrocaseous necrosis. Macrophages contained many small oval or round-shaped yeast-like cells and a few rod-shaped organisms indicating a narrow based budding in their cytoplasm. The yeast-like cells were 2-5 microns (average 3.5 microns) in diameter, and appeared as a central, spherical, lightly basophilic body surrounded by a clear zone or "halo". The cell wall and central body were stained by the periodic acid-Shiff, Grocott's methenamine silver impregnation, or Gridley fungus method. Immunohistochemically, yeast-like cells were positive to anti-histoplasma yeast antibody, and rod-shaped organisms were positive to anti-histoplasma mycelial antibody. The present paper describes the first case of canine histoplasmosis in Japan.