What Is Congenital Toxoplasmosis?
Congenital toxoplasmosis is an infection that occurs when the T. gondii parasite passes from a pregnant person to their baby. This happens if the mother acquires a new infection shortly before or during pregnancy, allowing the parasite to cross the placenta and infect the developing fetus. The impact on the baby varies greatly, depending primarily on when the infection occurs.
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Timing is critical. The risk of transmission and the severity of the illness are linked to the trimester of pregnancy. An infection in the first trimester has a lower chance of passing to the baby, but if it does, the health consequences are often more severe. Conversely, a third-trimester infection is much more likely to be transmitted, but the baby will probably have a milder case or no symptoms at birth.
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Often a silent condition. A large majority of infants born with congenital toxoplasmosis—up to 90 percent—appear healthy at birth. This lack of initial symptoms can make the condition difficult to diagnose without specific testing. However, problems like vision loss, hearing impairment, or learning disabilities can emerge months or even years later.
How Is the Infection Transmitted?
For a baby to develop congenital toxoplasmosis, the mother must first become infected with the T. gondii parasite. This common microscopic organism can be acquired from several everyday sources. Understanding these routes is key to prevention.
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Contact with cat feces. Cats are the parasite's primary host, and they shed it in their feces. This can contaminate soil, sandboxes, and litter boxes, posing a risk even to those who do not own a cat.
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Eating undercooked meat or shellfish. The parasite can form cysts in the muscle tissue of animals like pigs and sheep. If meat is not cooked to a safe temperature, these cysts can cause infection. Raw or undercooked shellfish can also be a source.
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Consuming unwashed produce or contaminated water. Fruits and vegetables can become contaminated from soil. Drinking from untreated water sources, like wells or streams, can also lead to infection. Proper handwashing and cleaning of kitchen surfaces is vital to prevent cross-contamination.
Signs, Symptoms, and Potential Complications
While many newborns with congenital toxoplasmosis appear healthy, others face serious challenges from birth. The specific signs often depend on when the maternal infection occurred and whether it was treated.
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Severe Eye Inflammation (Chorioretinitis). This is the most common complication, involving inflammation and scarring of the retina at the back of the eye. It can develop years after birth in children who initially seemed fine and can lead to significant vision loss if not treated.
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Impact on the Brain and Development. The parasite can cause a "classic triad" of symptoms: hydrocephalus (a buildup of fluid on the brain), intracranial calcifications (calcium deposits in brain tissue), and chorioretinitis. Other potential issues include seizures, an abnormally small head (microcephaly), cerebral palsy, hearing loss, and developmental disabilities. Early treatment can greatly improve the neurological outlook.
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Widespread Physical Symptoms. In severe cases, the infection can affect the entire body. Newborns may have a low birth weight, an enlarged liver and spleen, jaundice (yellowing of the skin and eyes), and a distinctive skin rash. Blood tests may also show anemia or a low platelet count.
Diagnosis, Treatment, and Prognosis
Identifying toxoplasmosis in a mother or baby is a multi-stage process that is crucial for a child's long-term health. Early and consistent medical care can make a significant difference in the outcome.
Diagnosis
The diagnostic process usually starts with the mother. Blood tests look for specific proteins (called IgG antibodies) that can signal a recent infection. If a new maternal infection is confirmed, doctors may recommend tests for the baby, such as an ultrasound or an amniocentesis, a procedure where a small sample of the amniotic fluid is tested for the parasite’s DNA. After birth, newborns suspected of having the infection undergo a full evaluation, including specialized blood tests, a detailed eye exam, and brain imaging like an MRI or CT scan.
Treatment
When a pregnant person is diagnosed, treatment aims to prevent the parasite from reaching the fetus. Early in pregnancy, a drug called spiramycin is often used. Later in the pregnancy, or if the fetus is known to be infected, doctors typically prescribe a combination of pyrimethamine and sulfadiazine (which actively fight the parasite) and folinic acid (which protects the patient from side effects). This same combination is used for a year-long treatment course for all infants with congenital toxoplasmosis, even those without symptoms.
Prognosis and Long-Term Care
A child’s outlook depends heavily on when the infection occurred and how quickly treatment began. Because problems can arise later in life, long-term follow-up is essential. This includes regular eye exams to monitor for chorioretinitis and ongoing developmental assessments to identify and address any potential hearing or learning delays.
Prevention and International Screening Policies
Given the serious potential outcomes of congenital toxoplasmosis, prevention is a major public health goal. However, nations differ widely in their screening strategies for pregnant people.
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Education and hygiene. Prevention starts with simple practices that directly counter the main transmission routes. Key steps include cooking meat to a safe temperature, thoroughly washing all fruits and vegetables, and avoiding direct contact with potentially contaminated cat feces by having someone else clean the litter box or by wearing gloves.
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Systematic screening in Europe. Countries like France and Austria have mandatory prenatal screening programs. Women are tested early in pregnancy and monitored if they lack immunity, allowing for immediate treatment if an infection occurs. This approach has drastically reduced the rate of severe outcomes.
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The U.S. approach. The United States does not include toxoplasmosis in its standard prenatal screening panel. Critics argue this policy misses opportunities for early treatment that could prevent lifelong disabilities in children, especially since the true number of cases is likely underestimated.
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The case for wider screening. While cost is often cited as a barrier, studies suggest that screening is cost-effective by preventing the lifelong expenses associated with disability. The availability of inexpensive, rapid tests further strengthens the argument for broader screening policies.
