Definition

Congenital toxoplasmosis is an infection in the fetus caused by the parasite Toxoplasma gondii, transmitted from mother to fetus during pregnancy. This infection can lead to miscarriage, stillbirth, or severe health issues in the newborn. In the United States, there are an estimated 400 to 4,000 cases of congenital toxoplasmosis reported annually.

Causes

Congenital toxoplasmosis is caused by the parasite Toxoplasma gondii, which can infect humans through several means, including:

• Consumption of raw or undercooked meat.
• Consumption of unwashed fruits or vegetables.
• Ingestion of water contaminated with the parasite or its eggs.
• Handling of contaminated soil or cat feces, followed by hand-to-mouth contact.

Infection process

The definitive host for Toxoplasma infection is cats, although other animals can serve as intermediate hosts. In cats, the parasite's life cycle can occur both inside and outside the intestine, while in other animals, it is limited to outside the intestine.

The parasite has three forms of transmission: tachyzoites, bradyzoites, and oocysts or sporozoites. Bradyzoites and tachyzoites represent slow and fast dividing phases, respectively. Oocysts are formed through the sexual cycle in the cat's intestine. Cats typically become infected by consuming animals containing bradyzoites or contacting water and soil containing oocysts.

Inside the cat's intestine, the parasite Toxoplasma gondii rapidly multiplies to produce oocysts. During the acute phase of infection, which lasts about 1-2 weeks, millions of oocysts are shed in the cat's feces. If ingested by the cat again, these oocysts transform into tachyzoites, restarting the cycle. When oocysts are ingested by humans, sheep, cows, pigs, birds, or rodents, they transform into either tachyzoites or bradyzoites, continuing the infection process.

Proliferating tachyzoites characterize acute infection. Conversely, Bradyzoites can be stored in tissues of intermediate hosts, such as the brain, heart muscle, skeletal muscle, and other organs, leading to latent infection—a condition in which the individual has been infected but does not experience symptoms or complaints.

Transmission to Humans

Toxoplasmosis can be acquired by pregnant women through two primary routes:

• Primary infection (first time) from consuming raw or undercooked food, drinking contaminated water, or handling contaminated soil.
• Reactivation of latent infection, particularly in individuals with compromised immune systems such as those with HIV/AIDS.

The parasite can be transmitted through the placenta from the mother to her fetus. The severity of the disease in the fetus depends on factors such as the timing of the infection during pregnancy, the parasite load, the parasite's virulence, and the mother's immune status.

Risk factor

Over 60% of people worldwide have been infected with Toxoplasma gondii. The incidence of Toxoplasma infection is particularly high in hot and humid climates and at low altitudes, where oocysts develop most rapidly in these favorable conditions.

If you become infected with the parasite during the first three months of pregnancy, your fetus has a 15-20% chance of experiencing severe congenital toxoplasmosis. However, if infection occurs in the third trimester of pregnancy, the likelihood of fetal infection rises to 60%.

Symptoms

The symptoms of congenital toxoplasmosis vary widely, ranging from asymptomatic (no symptoms) to severe, with some symptoms potentially appearing months, years, or even decades later. Infants with severe congenital toxoplasmosis typically show symptoms at birth or within the first six months of life. These symptoms may include:

• Premature birth, with most affected babies being born prematurely.
• Very low birth weight.
• Eye damage and vision problems.
• Jaundice (yellowing of the skin and whites of the eyes).
• Digestive complaints such as diarrhea or vomiting.
• Anemia (lack of red blood cells).
• Difficulty breastfeeding.
• Swollen lymph nodes.
• Enlarged liver and spleen.
• Macrocephaly is characterized by an abnormally large head size, and it may include hydrocephalus (fluid buildup in the brain).
• Microcephaly characterized by an abnormally small head size.
• Skin rash.
• Hearing loss.
• Calcification and brain damage due to parasitic infection.
• Seizures.
• Mild to severe mental retardation

Diagnosis

Congenital toxoplasmosis can be diagnosed through various tests. Initially, the doctor may conduct blood tests to detect the presence of the parasite. If these tests yield positive results, further prenatal testing may be recommended to assess the baby's infection status. These prenatal tests may include:

• Ultrasonography to evaluate for fetal abnormalities, such as hydrocephalus.
• Polymerase chain reaction (PCR) testing on amniotic fluid.
• Fetal blood tests.

If the baby exhibits symptoms suggestive of congenital toxoplasmosis, additional diagnostic tests may be performed, such as:

• Antibody tests on umbilical cord blood or cerebrospinal fluid.
• Further blood tests.
• Eye examinations.
• Neurological evaluations.
• Imaging studies like computed tomography (CT) scans or magnetic resonance imaging (MRI) of the baby's brain.

Management

Congenital toxoplasmosis can be treated both before and after birth. Treatment options before birth may include:

• Administration of antiparasitic and macrolide antibiotic drugs (such as spiramycin) to prevent transmission of the parasite from mother to child.
• Use of antiparasitic pyrimethamine and sulfadiazine antibiotics in the later stages of the first trimester if the fetus is confirmed to have a parasitic infection.
• Folic acid supplements to protect the bone marrow of both the mother and the fetus, which may become depleted due to pyrimethamine and sulfadiazine treatment.
• Administration of pyrimethamine, sulfadiazine, and folic acid for up to 1 year.
• Use of steroids if the baby's vision is threatened or if the fetus has high protein levels in its cerebrospinal fluid.

After birth, treatment for congenital toxoplasmosis may involve medications depending on the symptoms experienced by the baby.

Complications

The complications of untreated congenital toxoplasmosis may include:

• Blindness
• Deafness
• Intellectual impairment
• Severe growth retardation

The long-term prognosis for infants depends largely on the severity of symptoms. Parasitic infections generally pose more challenges during pregnancy if they occur early rather than late. However, if detected early enough, medications can be administered before the parasite infects the fetus.

Approximately 80% of babies with congenital toxoplasmosis may experience visual and learning difficulties throughout their lives. Some infants may even develop blindness and eye scars persisting for over 30 years after birth.

Prevention

Congenital toxoplasmosis can be prevented by:

• Cooking food thoroughly.
• Washing and peeling all fruits and vegetables.
• Frequently washing hands and cutting boards used for meat, vegetables, or fruits.
• Avoid drinking unfiltered water.
• Using gloves when gardening or avoiding gardening to avoid contact with soil that may contain cat feces.
• Avoid changing the cat litter box.

If you own a cat, you can choose to keep it even if infected with the Toxoplasma parasite. The risk of getting infected by your cat is very low. However, make sure someone else changes the cat litter box during your pregnancy.

When to see a doctor?

It is advisable to promptly visit a doctor if you experience signs of infection during pregnancy. These signs may include fever, nausea, vomiting, joint and muscle pain, and other flu-like symptoms. Toxoplasma infection in healthy adults typically does not cause severe symptoms, but it can interfere with fetal growth and development.

Additionally, regular prenatal check-ups are recommended so that the doctor can monitor the health of both the mother and the fetus and detect any abnormalities early on.

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