Identification of Histoplasma capsulatum organisms in the pleural and peritoneal effusions of a dog

Histoplasma capsulatum organisms were identified by cytologic evaluation in the thoracic and abdominal effusions of a 5-year-old sexually intact male Cocker Spaniel that was referred because of anorexia and lethargy. Treatment with amphotericin B and ketoconazole was instituted. The dog developed respiratory arrest, a complication of the disseminated disease, and died. Necropsy findings included pleural effusion, hepatomegaly, and enlarged tracheobronchial, hilar, mediastinal, and mesenteric lymph nodes. Granulomas containing periodic acid-Schiff (PAS)-positive yeast-like organisms identified as H capsulatum were seen in the lungs, liver, and lymph nodes. The lymphatic vessels were dilated, and fibrosis of the portal and periportal regions of the liver was noticed. Identification of Histoplasma organisms by cytologic examination of pleural and abdominal effusions is a rare laboratory finding and can provide a minimally invasive and inexpensive definitive diagnosis of histoplasmosis.