Detection of circulating antigens in the diagnosis of acute toxoplasmosis.

Using an enzyme-linked immunosorbent assay, we have found circulating antigens of Toxoplasma gondii in three models of murine toxoplasmosis: mice infected with trophozoites of the RH strain (acute toxoplasmosis), the Beverley strain (subacute toxoplasmosis), and the T626 strain (chronic toxoplasmosis). Circulating antigens were detected 48 hr after infection in the mice infected with the RH strain, and all mice had antigenemia by the fourth day. In those infected with the Beverley strain, circulating antigens were detected from the second day after inoculation until the end of the study, with a peak (71% of the infected mice) on day 10. Of those infected with the T626 strain, 40% had antigenemia at 13 days after infection. The detection of circulating antigens in serum is directly related to the presence of toxoplasmosis in the acute phase in the three models studied and, therefore, may prove very useful in the rapid diagnosis of this disease.