HISTOPLASMOSIS

Histoplasmosis is a fungal infection caused by the dimor­phic fungus Histoplasma capsulatum and can affect both humans and animals. The disease occurs in North, Central and South America, Africa, India and Southeast Asia.

Histoplasma capsulatum occurs in soil contaminated with bird and bat droppings. The host range of H. capsu- latum includes many animal species, but the clinical cases reported in European animals are few and mainly related to dogs, chinchillas¹-⁶) and Dorcas gazelle (Gazella dorcas neglecta) kept at a Spanish zoo⁽⁷⁾.

Infection most commonly occurs via the inhalation or ingestion of microconidia. The organism is transformed into the yeast phase at body temperature and phagocytized by alveolar macrophages, which can disseminate the infec­tion to other organs.

There are three main clinical manifestations: subclini- cal, respiratory and disseminated disease. The clinical signs observed in affected animals are: anorexia followed by weight loss, constipation and increased respiratory rate. Gastrointestinal signs characterize the disseminated disease. Generalized lymphadenopathy and pleural and peritoneal effusions have also been documented in disseminated forms. Anaemia and hypoalbuminaemia are the most common haematological abnormalities of disseminated histoplasmosis. At necropsy, numerous 3—6 mm white foci can be seen throughout the pulmonary parenchyma, liver, spleen and skeletal muscles.

Histoplasmosis is diagnosed by performing a cytological evaluation of tissues and effusions using haematoxylin and eosin (H&E) and PAS stains. A definitive diagnosis can be achieved by fungal culture.