SCID mouse models of acute and relapsing chronic Toxoplasma gondii infections.

Lymphodeficient scid/scid (SCID) mice died from acute infection with a strain of Toxoplasma gondii that causes chronic infection with mild symptoms in immunocompetent non-SCID mice. However, most SCID mice reconstituted with spleen cells from immunocompetent mice 1 month prior to T. gondii infection survived in good health after a transient period during which they appeared ill. Unreconstituted SCID mice given sulfadiazine in their drinking water from day 10 of Toxoplasma infection onward survived the acute phase of infection and lived for many weeks without overt symptoms. Histological examination revealed Toxoplasma cysts in their brains. However, if sulfadiazine was withdrawn from the drinking water of these chronically infected SCID mice, the mice died within 1 week with large numbers of trophozoites throughout their brains. These findings establish SCID mice as a potentially useful resource with which to study various aspects of immunological control of T. gondii infection during either its acute or chronic phase. Furthermore, the ability to produce chronic infections with avirulent T. gondii in SCID mice and to cause acute relapsing infections at will suggests that SCID mice may be helpful in evaluating potential therapies for acute and chronic T. gondii infections in immunocompromised patients.