Effects of freezing on the infectivity of Toxoplasma gondii cysts for white mice.

: The infectivity of Toxoplasma gondii cysts in the brains of mice, after storage at -21 degrees C for various periods of time, was studied by intraperitoneally inoculation into mice. Infective parasites were not demonstrated after freezing for 5 hours or longer. Even after 1 1/2 hours exposure to -21 degrees C, many cysts seemed to lose their infectivity. The role of low temperatures as a limiting factor in the epidemiology of cyst-induced toxoplasmosis, is discussed.