Experimental pythiosis in rabbits.

Rabbits were injected by subcutaneous, intraperitoneal and intravenous routes with suspensions of motile zoospores of a Pythium sp. isolated from a subcutaneous lesion of a horse in north Queensland. Some animals injected by the subcutaneous route were also treated by cortisone injections. Animals in each group were found to be highly susceptible to infection. Injection by the subcutaneous route resulted in progressive granulomatous eosinophilic abscesses in all normal and cortisone-treated animals. Preferential hepatic invasion developing into severe necrotizing hepatitis was the most common lesion in the intraperitoneally injected group. In intravenously injected animals severe embolic mycotic nephritis was the principal lesion. A significant progressive leukocytosis with moderate neutrophilia and mild monocytosis was observed in the subcutaneously and intraperitoneally injected immune competent animals. Cortisone-treated subcutaneously injected animals did not develop a leukocytosis. Many of the cortisone-treated control animals showed increased susceptibility to bacterial infections while the cortisone-treated fungal-injected animals did not.