The Resistance of the Encysted Form of Toxoplasma gondii

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Abstract
The cyst of Toxoplasma is capable of longer survival than the proliferative form when stored in infected tissues. Cysts of the Beverley strain survived as long as 68 days at 4[degree]C. While proliferative forms, free or in tissues, are destroyed by peptic juice. within a few minutes, tissue containing cysts remains infective for up to 3 hours. Parasites liberated by peptic juice from isolated cysts survive for 2 hours, even though the cyst wall is immediately destroyed. Proliferative forms survive exposure to 1% trypsin for at least 3 hours, but not as long as 6 hours. The cyst wall is immediately destroyed by trypsin; the liberated parasites survive at least 6 hours, the longest period tested. Cysts are rendered non-infective by exposure to distilled water for 30 minutes or less; even small concentrations of saline preserved their viability for longer periods. However, isolated cysts did not survive 24 hours in saline at room temperature. Cysts lose viability after 30 minutes at 50[degree]C and 10 to 15 minutes at 56[degree]C. There is some loss of viability after 1 hour at 45[degree]C. Freezing and drying render the cysts non-infective.

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