The most severe symptoms occur in the congenitally acquired form and in immunocompromised hosts. In the immunocompetent host, toxoplasmosis is divided into congenital, acquired, and ocular categories. The most common finding is lymphadenopathy. If the mother was infected prior to the current pregnancy, virtually no risk of fetal transmission exists. If the mother becomes infected during pregnancy, the fetus is at risk regardless of whether or not the mother is symptomatic.
Congenital infection is most severe if acquired in the first or second trimester.
Seventy-five percent of infants born with congenital toxoplasmosis infection will be asymptomatic. Eight percent will show severe CNS impairment, which might not manifest for several years. In the immunocompetent host, infection with T gondii may be indistinguishable from infectious mononucleosis. Ocular toxoplasmosis occurs from activation of cysts deposited in or near the retina. Focal, necrotizing retinitis is the characteristic lesion.