Microbiology · Year 2 · from Microbiology
Case 3: Toxoplasmosis in Pregnancy
Presentation
A 26-year-old pregnant woman at 14 weeks gestation is found to have Toxoplasma IgG and IgM antibodies positive on routine prenatal screening. She was seronegative at her first prenatal visit 8 weeks ago. She feels well with no symptoms. She has two cats at home and enjoys gardening. She recalls eating undercooked lamb at a dinner party about 6 weeks ago. She is very concerned about the effects on her baby.
Clinical Image
Diagram illustrating Toxoplasma gondii life cycle with cats as definitive hosts, transmission routes to humans (undercooked meat, cat feces in soil), and potential consequences of congenital infection.
Image Source: Lecture image - Toxoplasma transmission
Questions
- What is the significance of seroconversion during pregnancy?
- What are the potential consequences of congenital toxoplasmosis?
- How should this patient be managed?
- How could this infection have been prevented?
Answers
- Significance of seroconversion: Seroconversion during pregnancy (converting from IgG-negative to positive) indicates acute primary infection during gestation. This carries significant risk of vertical transmission to the fetus. The timing of infection relative to gestational age determines outcomes:
- First trimester: Lower transmission rate (10-15%) but more severe fetal effects
- Third trimester: Higher transmission rate (60-70%) but often milder or subclinical fetal infection
- Overall, earlier infection = more severe disease if transmitted
A positive IgG with negative IgM in early pregnancy would indicate prior immunity and low risk.
- Consequences of congenital toxoplasmosis: The classic triad is:
- Chorioretinitis: Most common manifestation; may cause vision impairment
- Hydrocephalus: From obstruction of the aqueduct of Sylvius
- Intracranial calcifications: Diffuse, scattered pattern (contrast with CMV which shows periventricular calcifications)
Other manifestations include hepatosplenomegaly, jaundice, seizures, and intellectual disability. Many congenitally infected infants are asymptomatic at birth but develop sequelae (especially chorioretinitis) later in life.
- Management approach:
- Confirm acute infection: IgG avidity testing (low avidity suggests recent infection), reference laboratory confirmation
- Amniocentesis: PCR of amniotic fluid to determine if fetus is infected (usually performed after 18 weeks and at least 4 weeks after maternal infection)
- Treatment:
- If maternal infection confirmed but fetal infection not yet confirmed: Spiramycin to reduce transmission
- If fetal infection confirmed: Pyrimethamine + sulfadiazine + leucovorin to reduce severity (after first trimester due to pyrimethamine teratogenicity)
- Serial fetal ultrasounds to monitor for hydrocephalus, calcifications
- Infectious disease and maternal-fetal medicine consultation
- Prevention:
- Cook meat thoroughly (tissue cysts killed at 67°C/153°F)
- Wash hands after handling raw meat
- Avoid unpasteurized goat's milk
- Wear gloves when gardening or handling soil
- Cat litter precautions: Have someone else change litter daily (oocysts require 1-5 days to sporulate and become infectious), or wear gloves; keep cats indoors
- Wash fruits and vegetables thoroughly
- Prenatal screening identifies susceptible women for counseling