Haematoloechus sp. infection in wild-caught northern leopard frogs (Rana pipiens).

Three male, wild-caught northern leopard frogs (Rana pipiens) died over a 1-week period with no previous history of clinical illness or disease. Noteworthy necropsy findings in one of the three frogs included depleted fat bodies in the coelomic cavity, indicating a poor nutritional condition, and a heavy parasite burden in the lungs. The location of infection and morphologic characteristics of the parasite were consistent with infection by the common lung fluke, Haematoloechus sp. In contrast to the heavy fluke load, only minor microscopic changes were observed in the lungs. Lesions included mild hypertrophy of the bronchiolar epithelium, with few submucosal inflammatory cells consisting predominantly of lymphocytes. Subsequent review of the literature revealed little about the pathologic effects of these parasites except that small numbers are thought to cause the host little harm. Our findings suggest that even with a large number of parasites, there is minimal pathologic impact in the lungs. We conclude that heavy lung-fluke infection should not be diagnosed as the sole or major etiology of death or illness in leopard frogs.