The Use of Tissue Culture-Grown Trophozoites of an Avirulent Strain of Toxoplasma gondii for the Immunization of Mice and Guinea Pigs

Experimental animals infected with avirulent strains of toxoplasma usually harbor cysts of this organism in their brains. The infection may be transferred to other animals by the injection of brain cysts but this technique possesses the disadvantage of difficulty in quantitating the inoculum. Trophozoites of avirulent strains of toxoplasma can be maintained easily in almost any type of tissue culture. Thus an ideal, constantly available supply of countable numbers of parasites may be used for experimental purposes. Using such methods, infections were established in mice and guinea pigs with avirulent toxoplasma grown in homologous tissue culture. Following infection both species of host rapidly developed immunity to a highly lethal challenge with a virulent strain of toxoplasma.