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Congenital Toxoplasmosis


Brenda L. Tesini

, MD, University of Rochester School of Medicine and Dentistry

Last full review/revision Jul 2020| Content last modified Jul 2020
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Congenital toxoplasmosis is caused by transplacental acquisition of Toxoplasma gondii. Manifestations, if present, are prematurity, intrauterine growth restriction, jaundice, hepatosplenomegaly, myocarditis, pneumonitis, rash, chorioretinitis, hydrocephalus, intracranial calcifications, microcephaly, and seizures. Diagnosis is by serologic or polymerase chain reaction testing. Treatment is with pyrimethamine, sulfadiazine, and leucovorin.

Toxoplasma gondii, a parasite found worldwide, causes congenital infection in about 1/10,000 to 80/10,000 births.

Etiology of Congenital Toxoplasmosis

Congenital toxoplasmosis is almost exclusively due to a primary maternal infection during pregnancy; however, there are exceptions, including reinfection with a new serotype of T. gondii or reactivation of toxoplasmosis in mothers with severe cell-mediated immunodeficiencies. Infection with T. gondii occurs primarily from ingestion of inadequately cooked meat containing cysts or from ingestion of oocysts derived from food or water contaminated with cat feces.

The rate of transmission to the fetus is higher in women infected later during pregnancy. However, fetuses infected earlier in gestation generally have more severe disease. Overall, 30 to 40% of women infected during pregnancy will have a congenitally infected child.

Symptoms and Signs of Congenital Toxoplasmosis

Pregnant women infected with T. gondii generally do not have clinical manifestations, but some may have a mild mononucleosis-like syndrome, regional lymphadenopathy, or occasionally chorioretinitis. Similarly, infected neonates are usually asymptomatic at birth, but manifestations may include

Diagnosis of Congenital Toxoplasmosis

  • Serial IgG measurement (for maternal infection)

  • Amniotic fluid polymerase chain reaction (PCR) testing (for fetal infection)

  • Serologic testing, brain imaging, cerebrospinal fluid (CSF) analysis, ophthalmologic evaluation (for neonatal infection), and PCR testing of various body fluids or tissues

Serologic testing is important in diagnosing maternal and congenital infection.

Maternal infection should be suspected if women have one or more of the following:

  • A mononucleosis-like syndrome and negative tests for Epstein-Barr virus, HIV, and cytomegalovirus (antibody or PCR)

  • Isolated regional adenopathy not due to another cause (eg, HIV)

  • Chorioretinitis

Acute maternal infection is suggested by seroconversion or a 4-fold rise between acute and convalescent IgG titers. However, maternal IgG antibodies may be detectable in the infant through the first year.

For fetal infection, PCR analysis of amniotic fluid is emerging as the diagnostic method of choice. There are numerous other serologic tests, some of which are done only in reference laboratories. The most reliable are the Sabin-Feldman dye test, the indirect immunofluorescent antibody (IFA) test, and the direct agglutination assay. Tests to isolate the organism include inoculation into mice and tissue culture, but these tests are not usually done because they are expensive, not highly sensitive, and can take weeks before yielding results.

For infants with suspected congenital toxoplasmosis, serologic tests, MRI or CT imaging of the brain, CSF analysis, brain stem auditory evoked responses, and a thorough eye examination by an ophthalmologist should be done. CSF abnormalities include xanthochromia, pleocytosis, and increased protein concentration. The placenta is inspected for characteristic signs of T. gondii infection (eg, placentitis). Nonspecific laboratory findings include thrombocytopenia, lymphocytosis, monocytosis, eosinophilia, and elevated transaminases. PCR testing of body fluids, including CSF, and tissues (placenta) can also be done to confirm infection.

Some states in the US do routine newborn screening to detect specific toxoplasmosis IgM antibody using dried blood.

Prognosis for Congenital Toxoplasmosis

Some children have a fulminant course with early death, whereas others have long-term neurologic sequelae. Occasionally, neurologic manifestations (eg, chorioretinitis, intellectual disability, deafness, seizures) develop years later in children who appeared normal at birth. Consequently, children with congenital toxoplasmosis should be closely monitored beyond the neonatal period.

Prognosis reference

  • 1. Yamamoto L, Targa LS, Sumita LM, et al: Association of parasite load levels in amniotic fluid with clinical outcome in congenital toxoplasmosis. Obstet Gynecol 130(2):335–345, 2017. doi: 10.1097/AOG.0000000000002131

Treatment of Congenital Toxoplasmosis

  • Sometimes spiramycin for pregnant women

  • Pyrimethamine, sulfadiazine, and leucovorin

Limited data suggest that treatment of infected women during pregnancy may be beneficial to the fetus (1 Treatment reference Congenital toxoplasmosis is caused by transplacental acquisition of Toxoplasma gondii. Manifestations, if present, are prematurity, intrauterine growth restriction, jaundice, hepatosplenomegaly... read more Treatment reference ). Spiramycin (available in the US with special permission from the U.S. Food and Drug Administration [FDA]) has been used to prevent maternofetal transmission but does not provide treatment to the fetus. Pyrimethamine and sulfonamides have been used later in gestation to treat the infected fetus.

Treatment of symptomatic and asymptomatic neonates may improve outcome. Therefore, treatment is begun with oral pyrimethamine (initial loading dose of 2 mg/kg once a day for 2 days followed by 1 mg/kg once a day, maximum 25 mg) and oral leucovorin (10 mg 3 times a week). Oral sulfadiazine (50 mg/kg 2 times a day, maximum 4 g) is begun after neonatal jaundice has resolved. After the initial 6 months of treatment, sulfadiazine and leucovorin are continued at the same dose, but pyrimethamine is given less frequently (only on Monday, Wednesday, and Friday). This regimen is continued for at least 6 more months. All treatment should be overseen by an expert. The use of corticosteroids is controversial and should be determined case by case but may be considered for active chorioretinitis or if CSF protein is > 1 gm/dL.

Treatment reference

  • 1. Olariu TR, Press C, Talucod J, et al: Congenital toxoplasmosis in the United States: Clinical and serologic findings in infants born to mothers treated during pregnancy. Parasite 26:13, 2019. doi: 10.1051/parasite/2019013

Prevention of Congenital Toxoplasmosis

Pregnant women should be counseled to avoid contact with cat litter boxes and other areas contaminated with cat feces. Because oocysts require > 24 hours after excretion to become infectious, conscientiously changing the entire litter box on a daily basis while wearing gloves followed by careful handwashing should reduce infection by this route if other members of the household cannot handle litter box chores.

Meat should be thoroughly cooked before consumption by pregnant women. Fruits and vegetables should be washed thoroughly or peeled, and all food preparation should be followed immediately by handwashing.

Women at risk of primary infection (eg, those frequently exposed to cat feces) should be screened during pregnancy. Women infected during the 1st or 2nd trimester should be counseled regarding available treatments.

Key Points

  • Congenital toxoplasmosis is usually due to a primary maternal infection acquired during pregnancy; reactivation of prior infection is of low risk except in immunocompromised women.

  • Many organs may be affected, including heart, liver, lungs, and central nervous system; the classic triad of findings consists of chorioretinitis, hydrocephalus, and intracranial calcifications.

  • Some children have a fulminant course with early death, whereas others have long-term neurologic and ophthalmologic sequelae (which may not develop for several years or even decades).

  • Do polymerase chain reaction (PCR) analysis of amniotic fluid (for fetal infection) or of body fluids (including cerebrospinal fluid) and tissues for neonatal infection; serologic testing may also be used.

  • Do MRI or CT of the brain.

  • Pyrimethamine, sulfadiazine, and leucovorin may help.

  • Pregnant women should avoid contact with cat litter boxes and other areas contaminated with cat feces.

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