Response of white mice to inoculation of irradiated organisms of the Toxoplasma strain RH.

Chemotherapeutic agents available for use against toxoplasmosis are usually not suitable for prophylactic purposes because of their toxicity. The observed increasing number of activated latent infections with Toxoplasma, especially in immune suppressed patients, requires that safe techniques are available for use during the patient's regression period. Pretreatment of mice with Toxoplasma killed by irradiation appeared to induce resistance to challenge with virulent organisms. Survival times of six months have been observed to date. Increasing effectiveness was seen after more than one administration. Further investigation into the duration of effective resistance is needed; the question of at which intervals subsequent inoculations should be performed in order to acquire a booster effect, if any, has still to be solved before application to man can be recommended.