[Mechanism of the persistence of a less virulent strain of Toxoplasma gondii in the body of the host].

The diameters of toxoplasms' cysts in native preparations of brain of bredless and inbred mice (AKR and CC57BR) infected with the toxoplasms of Czech low-virulent strain were measured. It is shown that the growth of cysts ceases by the 7th week from the infection and the ratio between cysts of different sizes does not change for 38 weeks and more. The curve of the ratio between cysts of different sizes, which in the period of infectious process stabilization is close to the even distribution curve, is apparently a result of primary parasitemia. By the 1st year of the infection a reactivation of the infection in some animals occurs judging by the rise of the number of small cysts. Stabilization and then reactivation of the infection are correlated with the dynamics of humoral antibodies.