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 (PC R-DEIA) was more sensitive than ethidium bromide staining after agaros e gel electrophoresis and as sensitive as nested PCR. PCR-DEIA, using common enzyme-linked immunosorbent assay (ELISA) methods, avoids agaro se gel electrophoresis for the identification of amplified products. T . gondii can also be detected with equal sensitivity in infected fibro blasts, but only after at least 8 days of cell culture. PCR-DEIA is th us recommended because of its sensitivity and convenience for detectin g early parasitemia in the surveillance of toxoplasmosis among pregnan t women and immunocompromised hosts. The courses of infection in mice infected with two strains of T. gondii were compared. Tachyzoites of t he virulent strain T. gondii RH, killing the host in 4 days, were iden tified in urine specimens and blood samples of mice 24 to 94 h after i noculation but not in brains, but no antibodies were detected, After i ntraperitoneal inoculation with cysts of the low-level virulence Bever ley 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 b rain from day 6 through day 525. By ELISA, high antibody titers were f ound from day II to day 525, with parasitemia preceding the appearance of antibodies. The usefulness of PCR-DEIA tests in conjunction with t he search for circulating antibodies for the early diagnosis of toxopl asmosis in humans is discussed.