Babesia argentina: the infectivity and immunogenicity of irradiated blood parasites for splenectomized calves

The intraerythrocytic forms of Babesia argentina were exposed to various doses of γ-radiation and then inoculated intravenously into splenectomized calves to study infectivity and immunogenicity of the irradiated parasites. Commencing with a dose of 8 krads, the proportion of organisms capable of multiplication in the host was progressively reduced until complete inhibition of multiplication was obtained with doses in the range of 50–70 krads. After exposures between 20 and 50 krads, the organisms showed reduced rates of multiplication in the host and produced only mild infections that left the surviving recipient animals strongly immune to reinfection. Parasites, completely inhibited by irradiation, did not protect splenectomized calves against challenge infection and behaved immunologically as killed organisms.