Detection of Toxoplasma gondii tachyzoites and bradyzoites in blood, urine, and brains of infected mice

Different techniques for identifying Toxoplasma gondii were compared. PCR was used to amplify part of the major surface antigen P30 gene of T. gondii. Amplified-DNA detection with the DNA enzyme immunoassay (PCR-DEIA) was more sensitive than ethidium bromide staining after agarose gel electrophoresis and as sensitive as nested PCR. PCR-DEIA, using common enzyme-linked immunosorbent assay (ELISA) methods, avoids agarose gel electrophoresis for the identification of amplified products. T. gondii can also be detected with equal sensitivity in infected fibroblasts, but only after at least 8 days of cell culture. PCR-DEIA is thus recommended because of its sensitivity and convenience for detecting early parasitemia in the surveillance of toxoplasmosis among pregnant women and immunocompromised hosts. The courses of infection in mice infected with two strains of T. gondii were compared. Tachyzoites of the virulent strain T. gondii RH, killing the host in 4 days, were identified in urine specimens and blood samples of mice 24 to 94 h after inoculation but not in brains, but no antibodies were detected, After intraperitoneal inoculation with cysts of the low-level virulence Beverley strain of T. gondii, parasites were identified in blood samples 4 days later and up to 17 days (but not in urine specimens) and in the brain from day 6 through day 525. By ELISA, high antibody titers were found from day II to day 525, with parasitemia preceding the appearance of antibodies. The usefulness of PCR-DEIA tests in conjunction with the search for circulating antibodies for the early diagnosis of toxoplasmosis in humans is discussed.