title: Augmentation of resistance to toxoplasma in mice by pretreatment with attenuated vaccine.
abstract: It is well known that certain chronic infectious diseases can be cured by preimmunization of the host against the live vaccine of an attenuated strain of an infectious agent from an attack of a virulent strain of same group of infectious agents. To test for the existence of a similar protective mechanism for Toxoplasma infection in mice, seven groups of mice were first infected with two kinds of low virulence strains (Beverley or S-273). They were challenged with a strong virulence strain (RH) from 2 to 59 weeks after the first immunization. All mice in one group challenged 2 to 3 weeks after the first Beverley immunization survived at rates of 33, 22 and 18 percent respectively, and mice examined at almost the same times after immunization with S-273 showed survival rates of 35, 19 and 52 percent respectively, which indicates a major difference in the number of surviving mice examined after 46-59 weeks. However, the majority of mice killed by a challenge with a virulent strain of Toxoplasma showed prolonged survival times of up to 10 days more than the non-immunized mice. Histological studies of dead mice showed acute bronchitis and/or bronchopneumonia, and a small number of tachyzoites was found in their lungs and other organs. All surviving mice harbored RH parasites in their brains. The present study suggested that mice treated with live vaccine of attenuated Toxoplasma acquired resistance against a challenge of a virulent strain of Toxoplasma. Since the infected mice showed small numbers of parasites and high antibody titers, the cause of death of premunitive mice from highly virulent Toxoplasma might differ from that of non-immune mice.
mesh_terms: D000818:Animals; D005260:Female; D006801:Humans; D007113:Immunity, Innate; D013997:Time Factors; D014122:Toxoplasma / Q000276:immunology*; D014124:Toxoplasmosis, Animal / Q000276:immunology*; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000276:immunology*
chemical_list: D014613:Vaccines, Attenuated