CPB 697 RESEARCH SEMINAR
Dinesh Singh, BVSc, MVSc, PhD
Graduate Student in Anatomic Pathology
Department of Comparative Pathobiology
Purdue University
“Disseminated Toxoplasmosis in American Red Squirrels (Tamiasciurus hudsonicus)”
Thursday, February 22, 2007
VPTH 112
3:30 p.m.
Abstract:
Toxoplasmosis is a systemic protozoal infection of zoonotic importance, caused by the apicomplexan protozoan Toxoplasma gondii. Domestic cats and wild felids are the only known definitive hosts whereas a variety of warm-blooded animals including humans, domestic animals, wild mammals, and birds serve as intermediate hosts. T. gondii infection has been reported in a variety of squirrels including eastern gray squirrel, Korean squirrel and the California tree squirrel. This is the first report of toxoplasmosis in American red squirrels (Tamiasciurus hudsonicus). American red squirrels, also known as Chickaree or the Hudson's Bay Squirrel, are distributed in the Rocky Mountain regions of the western United States, Appalachian Mountains, northeastern United States, Alaska and Canada.
Two juvenile male red squirrels were found dead and submitted for necropsy examination. At necropsy, the squirrels were lean with moderate ectoparasite infestation. Gross lesions were only observed in lungs from both squirrels. The lungs were diffusely mottled dark red to tan and consolidated. Numerous pale tan to creamy-white, oval to circular, up to 2 mm in diameter, nodules were scattered throughout the lungs. Microscopically, both lungs had diffuse necrotizing lymphohistiocytic pneumonia with intracellular as well as free protozoal organisms, morphologically consistent with T. gondii. There was multifocal lymphoplasmacytic encephalitis with intralesional protozoal organisms in both squirrels. Additional histologic lesions included lymphoplasmacytic periportal hepatitis and lymphoplasmacytic interstitial nephritis. Protozoal organisms in the lung tested positive for T. gondii by immunohistochemistry. Transmission electron microscopy of the lung demonstrated intracellular protozoa with morphologic features consistent with T. gondii. Real-time PCR for T. gondii was positive on samples of the lung, brain and kidney.
On the basis of histopathology, immunohistochemistry, transmission electron microscopy, and real-time PCR, disseminated T. gondii infection was determined to be the cause of death of these squirrels. The source of infection is not determined but is speculated to be through contamination of premises with oocysts from wild and/or domestic felids. Since red squirrels are common near urban settlements, this finding underscores their role as important intermediate hosts for T. gondii.