Pulmonary Lesions in Dogs with Experimental and Naturally Occurring Toxoplasmosis

The lungs of 92 dogs with confirmed toxoplasmosis were studied. Focal areas of coagulation necrosis, adjacent to and involving small vessels and bronchioles, and exudation of fibrin were the characteristic lesions produced by T. gondii in the lungs of dogs with both experimentally induced and naturally occurring infections. The inflammatory response to the areas of necrosis was minimal. Dogs inoculated intratracheally developed more extensive pulmonary lesions with greater numbers of T. gondii than dogs inoculated by the intravenous or subcutaneous route. Toxoplasma were not demonstrated in the pulmonary lesions after the 16th day following inoculation. Distemper was a concurrent infection in 20 cases of naturally occurring toxoplasmosis. The lesions produced by the two etiologic agents were distinctly different. Based on the severity of pulmonary lesions the dogs appeared to be primarily infected with toxoplasma.