Background
Can be acquired during maternal parasitemia associated with primary infection
However, it is possible to acquire from reactivation of latent toxoplasmosis in an HIV-infected mother
Risk of transplacental infection of fetus is lowest in first trimester and highest in third
Clinical Presentation
Often no history of illness during pregnancy
Symptoms, if present, tend to be mild with low-grade fever, malaise, and lymphadenopathy
At birth, 85% of infected babies are asymptomatic and only 15% are symptomatic
Risk of infection is related to trimester of infection: 6% in first, 40% in second, and 72% in third
Risk of signs of congenital infection is inversely related to trimester of infection: 61% in first, 25% in second, and 9% in third
Classic triad of chorioretinitis (most common), intraparenchymal cerebral calcifications , and hydrocephalus
Others: thrombocytopenia , hepatitis , hepatosplenomegaly , cataracts , strabismus , microphthalmia
Diagnosis
In pregnancy
Molecular
Definitive diagnosis is based on PCR of amniotic fluid around 18 months, usually done after maternal serology to confirm intrauterine infection
Sensitivity is 64 to 92% and specificity 100% (NPR around 88 to 98%)
Earlier than 18 weeks has unknown sensitivity and specificity, and has a higher risk of spontaneous abortion
Can also be done on fetal blood
Serology
Can check maternal IgM and IgG
IgM is not specific to recent infection, however, as it can be present for more than a year
IgG avidity testing is used to determine recency of infection
Low avidity is 35-50% and high is >60%
Low avidity is unhelpful, as avidity can remain low for more than a year
High avidity, on the other hand, suggests infected at least 3-4 months prior
Therefore, if infection is suspected in the first 16 weeks of gestation, avidity testing may be able to rule out infection during pregnancy
Needs serial head ultrasound to monitor for hydrocephalus and intraparenchymal brain calcifications
May also see hepatic calcifications, splenomegaly, and ascites
In children
Standard workup starts with serology, then adds PCR and other investigations if clinical suspicion is high
Serology
In neonates, IgG serology reflects maternal status, so use IgM and IgA instead
Molecular testing
If clinical suspicion is high, add PCR of the peripheral blood, urine, and CSF to the serology
Other
If clinical suspicion is high, also get ophthalmologic evaluation, hearing assessment, ultrasound or CT of the brain, and lumbar puncture
Management
In pregnancy
If infected < 14 weeks gestation, spiramycin 3 g/day until delivery
However, it doesn't cross the placenta and it's unclear whether it affects outcomes in the baby
Likely most effective if given within 8 weeks of maternal infection
Second-line would be monotherapy with sulfadiazine or clindamycin
If age ≥ 14 weeks gestation and documented fetal infection, or if suspected infection was ≥14 weeks gestation, use standard therapy
Standard therapy is: pyrimethamine 50 mg q12h for 2 days followed by 50 mg daily (plus folinic acid 10-20 mg daily until 1 week after stopping pyrimethamine), and sulfadiazine 75 mg/kg load followed by 50 mg/kg q12h (maximum 4 g/day)
This treatment crosses the placenta, which is why it is used in cases of documented or suspected fetal infection, as well as in later-term infections when the risk of fetal infection is higher
Therefore, if initially started on spiramycin , then switch to standard therapy if amniotic fluid PCR is positive or ultrasound is abnormal
However, it is teratogenic until 14 weeks gestation so spiramycin is used until then