Diagnosis and management of Toxoplasma infection in the neonate

 An infant infected with Toxoplasma gondii in utero may not have demonstrable IgM either at birth or on subsequent testing reportedly in up to 50% of cases. Specific IgG in the neonate serum may be actively produced or passively acquired from the mother. Consequently when a neonate is found to have Toxoplasma specific IgG but not IgM the diagnosis remains uncertain. Detection of specific IgA is under assessment and may be a more sensitive indicator of congenital infection.

•  However, if maternal booking clinic and current serum samples are tested for IgM and found to be negative, congenital toxoplasma infection may be excluded. If the maternal samples are found to contain specific IgM, the status of the neonate can be established by testing serum samples at 2 monthly intervals to document any loss of passively acquired antibody.
• Persistence of specific IgG at the age of one year confirms the diagnosis of congenital toxoplasmosis.
• Other investigations which may be helpful include parasite isolation/detection in appropriate foetal/neonatal samples and radiography.

In summary, the initial investigation of a neonate suspected of having congenital toxoplasmosis should involve the testing of current maternal and infant sera as well as a maternal booking clinic sample. Whenever possible, all three samples should be sent for Toxoplasma serology as well as a sample of neonatal whole blood in anticoagulant.

Anti-parasitic therapy is indicated when clinical signs of toxoplasmosis are noted or laboratory findings indicate infection. When the neonate is asymptomatic and laboratory results are equivocal, potentially toxic antiparasitic drugs should be withheld.