TOXOPLASMA-GONDII - EXPERIMENTAL-INFECTION IN CATS VACCINATED WITH CO-60-IRRADIATED TACHYZOITES

The effects of Co-60-irradiation on the viability and immunogenicity o f RH and Beverley strains of Toxoplasma gondii was examined. While Co- 60-irradiated tachyzoites retained invasive activity in mouse embryona l cells and sustained antigenicity in mouse peritoneal macrophages, th e parasites did not develop in host cells. Vaccination of mice with Co -60-irradiated tachyzoites of either RH or Beverley strains induced re sistance to challenge with a highly virulent strain (RH strain), Vacci nation of kittens with Co-60-irradiated tachyzoites of the Beverley st rain partially prevented oocyst shedding when challenged with cysts (b radyzoites) from the Beverley strain. But kittens vaccinated with Co-6 0-irradiated or fixed tachyzoites of the RH strain shed oocysts when c hallenged with cysts (bradyzoites) from the Beverley strain, These res ults suggest that the development of protective immunity in feline tox oplasmosis seems to be strain and/or stage-specific.