Gordon D. Wallace

Observations on a feline coccidium with some characteristics of Toxoplasma and Sarcocystis

SummaryTwo morphologically different cysts were found in skeletal muscles of mice inoculated with fecal material from a stray cat containing Isospora-type oocysts. The most common cyst contained bradyzoites resembling those of Toxoplasma and resulted from an oocyst measuring 11×13 μm which appeared to be identical to that of Toxoplasma. The other cyst, observed in only a few mice, contained bradyzoites resembling those of Sarcocystis, but the oocyst or sporocyst that gave rise to it was overlooked and apparently lost.Two more strains of the parasite resembling Toxoplasma were found in feces of stray cats. When inoculated into mice, the oocyst of this parasite routinely produced chronic infection and formed cysts similar to Toxoplasma in skeletal muscles and occasionally in the central nervous system. The majority of infected mice developed Toxoplasma antibody, but only to low titers. Cats fed carcasses of infected mice remained healthy and shed nonsporulated oocysts following a prepatent period of about 5 days. Cats did not develop Toxoplasma antibody. There was little or no cross immunity between the parasite and T. gondii in cats or mice. Transmission of the parasite between mice by the cyst stage normally was not possible; however, mice inoculated with cortisone acetate did become infected when inoculated with cysts. In other laboratory animals inoculated orally with the oocyst asymptomatic infection was detected in 3 species of rats, in guinea pigs and in dogs, but not in monkeys, pigeons or Japanese quails. Fluorescent antibody tests on human sera failed to provide evidence of natural human infection with the parasite.

Sarcocystis in mice inoculated with Toxoplasma-like oocysts from cat feces.

Sarcocysts morphologically similar to Sarcocystis muris were observed in mice after inoculation with Toxoplasma-like oocysts found in feces of a stray cat. Cats that were fed mice infected with the oocysts shed similar oocysts in their feces. Sarcocysts were found histologically in about 50 percent of mice inoculated with 40,000 or more oocysts and examined 42 days or longer after exposure. Most inoculated mice developed low Toxoplasma dye-test antibody titers 3 to 4 weeks after exposure, but Toxoplasma antibody was usually not detectable in infected cats.