The diagnosis of congenital toxoplasmosis can be difficult.
Demonstration of maternal seroconversion during pregnancy can help to identify an infant at risk.
The presence of IgG antibodies in the infant at birth is non-diagnostic since these could have undergone transplacental transfer.
Tests on infant’s blood:
(1) IgM and IgA antibodies
(2) persistence of IgG positivity after maternal antibodies gone (after 4 months of age)
A negative IgM antibody does not exclude the diagnosis since IgM could revert to normal in an infection occurring early in the pregnancy.
Tests on neonates CSF:
(1) PCR
Tests on amniotic fluid:
(1) PCR
(2) injection into mice
Combinations of tests give better results than a single test alone.
Continued follow-up during infancy may detect cases of congenital toxoplasmosis with negative tests during or after birth, especially if only limited testing was done.
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