Unrecognized ingestion of Toxoplasma gondii oocysts leads to congenital toxoplasmosis and causes epidemics in North America

Abstract

Background: Congenital toxoplasmosis presents as severe, life-altering disease in North America. If mothers of infants with congenital toxoplasmosis could be identified by risks, it would provide strong support for educating pregnant women about risks, to eliminate this disease. Conversely, if not all risks are identifiable, undetectable risks are suggested. A new test detecting antibodies to sporozoites demonstrated that oocysts were the predominant source of Toxoplasma gondii infection in 4 North American epidemics and in mothers of children in the National Collaborative Chicago-based Congenital Toxoplasmosis Study (NCCCTS). This novel test offered the opportunity to determine whether risk factors or demographic characteristics could identify mothers infected with oocysts.

Methods: Acutely infected mothers and their congenitally infected infants were evaluated, including in-person interviews concerning risks and evaluation of perinatal maternal serum samples.

Results: Fifty-nine (78%) of 76 mothers of congenitally infected infants in NCCCTS had primary infection with oocysts. Only 49% of these mothers identified significant risk factors for sporozoite acquisition. Socioeconomic status, hometown size, maternal clinical presentations, and ethnicity were not reliable predictors.

Conclusions: Undetected contamination of food and water by oocysts frequently causes human infections in North America. Risks are often unrecognized by those infected. Demographic characteristics did not identify oocyst infections. Thus, although education programs describing hygienic measures may be beneficial, they will not suffice to prevent the suffering and economic consequences associated with congenital toxoplasmosis. Only a vaccine or implementation of systematic serologic testing of pregnant women and newborns, followed by treatment, will prevent most congenital toxoplasmosis in North America.

Figure 1.

Distribution of mothers with and without antibody to sporozoites in each year, 1981–1999.

Figure 2.

Lack of correlation between presence of antibody to sporozoites in maternal serum samples and month of birth of child.

Figure 3.

Lack of correlation of antibody to sporozoites in maternal serum samples with hometown location and hometown size. Mothers with serum antibody to sporozoites and cysts are distributed across rural, urban, and suburban regions in the United States.

Figure 4.

Lack of correlation of antibody to sporozoites in maternal serum samples with presence of maternal illness. Mothers’ symptoms include lymphadenopathy, fever, night sweats, headache, and influenza-like illness.

Figure 5.

Lack of correlation of antibody to sporozoites in maternal serum samples and manifestations of infection in the newborn infant. ^aSevere disease is defined in references [14].