Antigenemia in recently acquired acute toxoplasmosis.

An enzyme-linked immunosorbent assay (ELISA), designed to detect low concentrations of antigens of Toxoplasma gondii, was used to determine whether antigenemia is present in patients with recently acquired acute toxoplasmosis. The ELISA detected antigenemia in 15 (65.2%) of 23 sera from 22 patients with recently acquired acute toxoplasmosis. Antigenemia was not detected in sera from 28 normal (seronegative for antibodies to Toxoplasma) individuals or from 55 individuals chronically infected with T. gondii. Sera from 13 individuals who were not infected with Toxoplasma but who had circulating rheumatoid factor were positive with normal and Toxoplasma-infected rabbit IgG but not with the F(ab)2 fractions. Sera from each of the 15 patients in the acute phase of infection did react with the F(ab)2 fraction of Toxoplasma-infected rabbit IgG but not with the F(ab)2 fraction of normal rabbit IgG. In preliminary studies, toxoplasma antigens were also detected in amniotic fluid and cerebrospinal fluid of newborns with congenital toxoplasmosis.