Congenital toxoplasmosis results from the vertical transmission of Toxoplasma gondii, a common protozoan parasite, from an infected pregnant woman to her fetus. The clinical presentation in the neonate is varied and may include a constellation of CNS manifestations and severe long-term sequelae. The diagnosis is based on thorough history, physical exam, laboratory testing, and imaging.
Congenital toxoplasmosis is caused by Toxoplasma gondii, a common protozoan parasite . In congenital cases, this organism is transmitted from the mother to the fetus through the placenta. The earlier the infection during pregnancy, the more severe the clinical symptoms . More than half of healthy pregnant women with primary infection are asymptomatic while those with symptoms exhibit low-grade fever, fatigue, myalgia, and lymphadenopathy. Approximately 25% of infected pregnant women will transmit the infection to the fetus .
Risk factors include having a cat, exposure to cat litter or contaminated soil, consumption of unfiltered water, raw or insufficiently cooked meat, or raw or dirty fruits or vegetables   .
While three-quarters of neonates with congenital toxoplasmosis are asymptomatic, the clinical presentation in affected patients is variable and includes a vast array of manifestations . This illness is characterized by a classic triad of hydrocephalus, chorioretinitis, and intracranial calcifications . Moreover, severe cases could feature microcephaly, fever, rash, jaundice, hepatosplenomegaly, seizures, sepsis-like illness, meningitis, and encephalitis  . Further possible manifestations include but are not limited to deafness, thrombocytopenia, myocarditis, pneumonitis, respiratory distress, and nephrotic syndrome .
Patients with congenital toxoplasmosis may exhibit findings such as a fever, rash, lymphadenopathy, hepatosplenomegaly. Affected neonates are likely to feature microcephaly or macrocephaly accompanied by bulging fontanelles and abnormal ophthalmologic findings.
In neonates and infants suspected to have congenital toxoplasmosis, the workup should include a careful consideration of the maternal history and all possible risk factors, a thorough physical exam including ophthalmologic assessment, and the appropriate studies.
Prenatal diagnosis is confirmed by the demonstration of Toxoplasma gondii in the amniotic fluid and/or fetal tissue through various techniques . Polymerase chain reaction (PCR) of the amniotic fluid is the most commonly used method and is typically diagnostic  . Moreover, PCR can be performed on cerebrospinal fluid (CSF), blood, or other bodily fluids . Other serologic tests include the Sabin-Feldman dye test, which is a reference study and not widely available, and the indirect fluorescent antibody (IFA) and indirect hemagglutination tests. Also, the organism can be isolated with mouse inoculation.
Of importance, Toxoplasma gondii - specific IgM antibodies have a prolonged presence, which makes it difficult to interpret whether the current infection is acute of chronic . However, an IgG avidity test is more accurate in diagnosing an acute infection and pinpointing the time of infection  . This is best performed early in pregnancy.
The diagnosis of congenital toxoplasmosis in an infant is confirmed by the persistent presence of Toxoplasma gondii - specific IgG by the twelveth month of life . Note that IgA and IgE enzyme-linked immunosorbent assay (ELISA) should be obtained once the infant's Toxoplasma gondii - specific IgM is negative.
Further laboratory studies are also essential. For example, a complete blood count (CBC) with a differential analysis in affected individuals is associated with thrombocytopenia, lymphocytosis, and monocytosis . Additionally, CSF analysis typically reveals xanthochromia and pleocytosis. Other important tests include plasma creatinine levels, liver function tests (LFTs), as well as urinalysis and urine culture.
Fetal assessment should include prenatal ultrasonography, which detects associated abnormalities.