Histoplasmosis.

Histoplasmosis is the most commonly diagnosed major systemic mycosis in dogs and the second most commonly reported fungal infection in cats. The causative organism, Histoplasma capsulatum, is endemic in 31 of the 48 contiguous US states and has a worldwide distribution. Histoplasma organisms enter the body via inhalation or, possibly, ingestion. They are phagocytized by macrophages and can be disseminated via the bloodstream or lymphatic system to the reticuloendothelial and gastrointestinal (GI) systems and, sometimes, the bones, skin, eyes, or brain. Clinical signs are often nonspecific, including lethargy, weight loss, and inappetence, although respiratory or GI signs may help localize the infection. Definitive diagnosis requires identification of H. capsulatum on cytology or histopathology. However, antigen testing may be useful in animals in the future. Itraconazole is the treatment of choice. The prognosis is fair for animals with pulmonary histoplasmosis and guarded to poor for those with GI or disseminated disease.