Toxoplasmosis in pregnancy
From IDWiki
Clinical Manifestations
- Often no history of illness during pregnancy
- Symptoms, if present, tend to be mild with low-grade fever, malaise, and lymphadenopathy
- Only half of women can identify a significant risk factor1
- Risk of transmission to fetus is with parasitemia associated with primary infection, so women who are seropositive are not at risk of having a child with congenital infection
Diagnosis
- 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
- Definitive diagnosis is based on PCR of amniotic fluid around 18 months, usually done after maternal serology to confirm intrauterine infection
- Serology
- Can check maternal IgM and IgG, both of which appear within the first week after infection
- 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, high avidity effectively rules out infection acquired during pregnancy
- Needs serial head ultrasound to monitor for hydrocephalus and intraparenchymal brain calcifications
- May also see hepatic calcifications, splenomegaly, and ascites
Management
IgM | IgG | Interpretation | Management |
---|---|---|---|
+ | – | acute primary infection or false positive | repeat serology in 2 to 3 weeks; if unchanged, then was false positive |
+ | + | recent or prior infection | high IgG avidity: infection was >4 months ago so unlikely to be acute |
low IgG avidity: cannot determine when infection occurred | |||
– | + | remote infection | no risk of transmission except rare cases of immunocompromise |
– | – | no prior infection; at risk | counsel on prevention of primary infection |
- In general, for highly suspected or confirmed infection, it is reasonable to start spiramycin while confirming the infection
- If acute infection, such as IgM + / IgG – that converts to IgG +, or IgM + / low IgG avidity with compatible clinical picture, then rule out fetal infection with an amniocentesis after week 18
- 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
- Pyramethamine is contraindicated in pregnancy before 14 weeks gestation
- Second-line would be monotherapy with sulfadiazine or clindamycin
- If age ≥ 14 weeks gestation and documented fetal infection by amniocentesis, 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
- If age ≥33 weeks gestation, then continue spiramycin and await a postnatal diagnosis
Prevention
- Prevention mostly focusses on counselling around risk reduction:
- Wash hands after changing cat litter
- Wear gloves in the garden and when changing cat litter
- Cook meat thoroughly
- Avoid raw eggs and unpasteurized dairy
- Wash fruits and vegetables
- Do not obtain a new cat while pregnant
References
- ^ K. Boyer, D. Hill, E. Mui, K. Wroblewski, T. Karrison, J. P. Dubey, M. Sautter, A. G. Noble, S. Withers, C. Swisher, P. Heydemann, T. Hosten, J. Babiarz, D. Lee, P. Meier, R. McLeod. Unrecognized Ingestion of Toxoplasma gondii Oocysts Leads to Congenital Toxoplasmosis and Causes Epidemics in North America. Clinical Infectious Diseases. 2011;53(11):1081-1089. doi:10.1093/cid/cir667.