Possible reasons for failure of conventional tests for diagnosis of fatal congenital toxoplasmosis: report of a case diagnosed by PCR and immunoblot.

Diagnosis of subclinical congenital toxoplasmosis has to rely on serological methods or isolation of the parasite. We present a case of congenital toxoplasmosis, in which conventional tests failed to establish the diagnosis. It was shown that this infant developed an intrathecal antibody response that was directed only against one of two Toxoplasma gondii strains used for routine diagnosis. In contrast to conventional tests, the diagnosis of cerebral toxoplasmosis could be established by using immunoblot and polymerase chain reaction (PCR). We therefore suggest that in unclarified cases, PCR and immunoblot, using at least two different strains of T. gondii, should be considered as additional tools for diagnosis of an infection with Toxoplasma and that examination of cerebrospinal fluid may be critical.