Toxoplasmosis is an infection caused by a microscopic parasite called Toxoplasma gondii , which is commonly found in undercooked meat, contaminated soil and water, and the feces of infected cats. For most healthy individuals, the infection causes mild, flu-like symptoms or no symptoms at all. However, when a pregnant person contracts toxoplasmosis for the first time, the parasite can cross the placenta and infect the developing fetus, a condition known as congenital toxoplasmosis. This transmission from mother to child is particularly dangerous because the fetus's immune system is not mature enough to fight the infection, potentially leading to severe and lifelong health problems, including a range of significant birth defects. Understanding these risks is crucial for prevention and for managing the health of infants who are born with the infection.
The most severe and historically recognized birth defects associated with congenital toxoplasmosis are often referred to as the "classic triad." These three primary conditions highlight the parasite's tendency to affect the central nervous system and the eyes. The first component is chorioretinitis, an inflammation of the back of the eye that can cause scarring on the retina, leading to impaired vision or, in severe cases, blindness. The second is the presence of intracranial calcifications, which are small deposits of calcium in the brain that mark areas where the parasite has caused tissue damage. The third is hydrocephalus, commonly known as "water on the brain," a condition where cerebrospinal fluid builds up within the skull, causing the head to enlarge and putting harmful pressure on the brain. Beyond this triad, congenital toxoplasmosis can cause a wider spectrum of neurological issues, including seizures, significant developmental delays, intellectual disabilities, and problems with muscle tone and motor control.
While the brain and eyes are primary targets, congenital toxoplasmosis can also affect other organ systems, leading to a variety of issues that may be apparent at birth. Some newborns with the infection may present with a different set of problems, which can include:
- An enlarged liver and spleen (hepatosplenomegaly)
- Jaundice, which is a yellowing of the skin and eyes
- A low red blood cell count (anemia)
- A rash or small, pinpoint-sized red spots on the skin (petechiae) from bleeding underneath
- Hearing loss, which can range from mild to profound
A critical aspect of congenital toxoplasmosis is that many infected infants show no obvious signs of illness at birth. They may appear completely healthy, but the infection can remain dormant in their bodies for years. These children are at risk of developing symptoms later in childhood or even as young adults. The most common delayed-onset problem is chorioretinitis, which can flare up and cause new eye damage and vision loss years after birth. For this reason, early diagnosis through newborn screening (if available) and long-term medical follow-up are essential for any child known to have been exposed to toxoplasmosis in the womb, allowing for timely treatment to prevent or minimize long-term damage.
How to tell if baby has toxoplasmosis?
Determining if a baby has toxoplasmosis requires medical testing, as the majority of infected infants show no symptoms at birth. If a maternal infection is suspected or confirmed during pregnancy, doctors can perform a series of evaluations on the newborn. Diagnosis typically involves a combination of blood tests to detect specific toxoplasmosis antibodies (IgM, IgA, and IgG), imaging of the brain like an MRI or CT scan to check for characteristic calcifications or cysts, and a thorough ophthalmologic exam to look for eye damage like chorioretinitis. In some cases, diagnosis can be confirmed by testing the baby's cerebrospinal fluid or by a positive newborn screening test, which is performed routinely in a few states. Before birth, an ultrasound or amniocentesis can also be used to check the fetus for signs of infection.
Is congenital toxoplasmosis rare?
While the parasite that causes toxoplasmosis is quite common, affecting about a third of the world's population, congenital toxoplasmosis is relatively rare, with incidence rates varying significantly by geographic region. The global rate is estimated at 1.5 cases per 1,000 live births, but it is considerably lower in many developed nations. For example, the incidence in the United States is approximately 0.5 cases per 10,000 live births, and the overall notification rate in the European Union/European Economic Area (EU/EEA) was 5.08 cases per 100,000 live births in 2020. The disease burden is known to be higher in other parts of the world, such as South America, and even within Europe, reported cases vary widely due to different screening policies and true differences in prevalence.
What happens if a fetus gets toxoplasmosis?
If a fetus is infected with toxoplasmosis, it can lead to serious complications, including miscarriage, premature birth, or slow growth. While some newborns may not show any symptoms at birth, they can develop significant health issues over time. At-birth problems can include a small head (microcephaly), jaundice, an enlarged liver and spleen, and inflammation of the brain, eyes, heart, or lungs. The long-term consequences are often severe and may include blindness from eye inflammation, hearing loss, seizures, and intellectual disability, with some of these issues emerging years after birth if the infection is left untreated.
Do all cats carry toxoplasmosis?
Not all cats carry the Toxoplasma gondii parasite, and even fewer are actively infectious. A cat must first become infected, which typically occurs when it eats contaminated prey like rodents or birds, or is fed infected raw meat. Even when a cat contracts the parasite, it only sheds the infectious eggs (oocysts) in its feces for a very limited time, usually for only one to two weeks following its first exposure. After this brief period, the cat develops immunity and is very unlikely to shed the parasite again. Therefore, many cats, particularly those kept strictly indoors who do not hunt or eat raw meat, may never become infected or pose a risk of transmitting toxoplasmosis.
What is the number one cause of toxoplasmosis?
The leading cause of toxoplasmosis in humans is foodborne transmission. This primarily occurs through the ingestion of tissue cysts found in undercooked or raw meat, with pork being a major source of infection in Europe and the United States. Another significant pathway is the ingestion of food, water, or soil contaminated with Toxoplasma gondii oocysts. These oocysts are shed in the feces of infected cats—the parasite's definitive host—and can remain infectious in the environment for over a year, contaminating sources like unwashed garden vegetables. While cats are essential to the parasite's life cycle, most human infections are acquired through the consumption of contaminated food and water rather than direct contact with felines.
Does toxoplasmosis affect future pregnancies?
Generally, a past toxoplasmosis infection does not pose a risk to future pregnancies. After a primary infection with T. gondii , your body develops specific antibodies and a lifelong immunity that protects a future fetus from the parasite. The main danger of congenital toxoplasmosis arises when a woman contracts the infection for the first time during pregnancy or just before conceiving, as her immune system has not yet mounted a protective response. While the parasite remains dormant in the body for life, it is typically only able to reactivate and pose a potential threat in the rare case that the mother becomes severely immunocompromised from conditions like HIV or certain medications.
What are the congenital abnormalities of toxoplasmosis?
Congenital toxoplasmosis can cause a range of serious abnormalities in a developing fetus or newborn, though many infected infants appear normal at birth. The most well-known issues form a classic triad of symptoms: hydrocephalus (excess fluid in the brain), intracranial calcifications, and chorioretinitis (a severe eye infection that can lead to blindness). Other potential neurological problems include microcephaly, seizures, and irregularities in brain tissue, which can result in later developmental delays with mental and motor skills. Beyond the nervous system, abnormalities can involve an enlarged liver or spleen, jaundice, heart disorders, and severe intrauterine growth restriction. Even if not present at birth, some issues, particularly eye infections and hearing loss, can appear later in childhood or adolescence.
