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
  • 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

  1. ^  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.