Overview

Congenital toxoplasmosis is a parasitic infection caused by Toxoplasma gondii (T.gondii) that is passed from an infected mother to her fetus during pregnancy. Many cases of this infection are present without symptoms at birth. As a result, this condition can cause serious, irreversible complications. These can include brain damage, visual impairment, and developmental delays. The parasite can cross the placenta at any stage of pregnancy, and the risk of transmission increases in later stages. However, earlier infections tend to cause more severe damage to the developing brain and eyes. When pregnant women are tested in time and treatment is given quickly, the chance of preventing or reducing long-term damage is much higher.¹

Epidemiology

Rates of congenital toxoplasmosis vary based on region, and the number of infections and the severity of illness can vary widely. For example, the parasite can survive and spread more easily in warm, humid conditions, so infections are more common in certain regions where these climates are present.² In places with strong food safety practices, clean water supplies, and reliable healthcare systems, the risks of infection tend to be much lower and better controlled. Another challenge is that this parasite is often difficult to detect. Many mothers never notice they are infected, and babies may not show signs immediately. This means that some cases are missed, especially where regular pregnancy check-ups are not available. As a result, some cases are missed altogether, mainly in areas where regular pregnancy check-ups and prenatal screening are not available or accessible to all. When the condition is recognised early, however, there are opportunities for treatment which can make a significant difference to the health and development of the child. 

Causes and transmission

Toxoplasma gondii is a parasite that completes its sexual life cycle in cats, the definitive hosts. The parasite can infect a wide range of warm-blooded animals, including humans. 

Common routes of maternal infection include eating contaminated raw or undercooked meat, consuming contaminated unwashed fruits or vegetables, and handling soil or cat litter contaminated with infected cat faeces. Drinking untreated water has also been recognised as a source in some outbreaks.

When a woman acquires a primary T. gondii infection during pregnancy, the parasite can cross the placenta and infect the fetus. The likelihood of transmission is lowest during the first trimester. Still, the potential damage is greatest at this stage as the foetus’s vital organs, such as the eyes and brain, are rapidly developing during this period (fetal organogenesis). Infections in the second and third trimesters are more likely to be transmitted but tend to cause less severe acute disease.³

Risk factors

Several factors increase the risk of congenital toxoplasmosis, including:

• Maternal primary infection during pregnancy
• Frequent consumption of undercooked or cured meats
• Poor kitchen hygiene leads to cross-contamination between raw meat and ready-to-eat foods
• Handling cat litter or soil without gloves
• Living in or travelling to high-prevalence regions
• Drinking untreated water in areas with poor sanitation
• Lack of prenatal screening 

Signs and symptoms

Congenital toxoplasmosis can present with a wide range of clinical manifestations from severe disease apparent at birth to completely silent infection that only becomes evident years later.⁴

The classic triad includes:

• Chorioretinitis
• Hydrocephalus
• Intracranial calcifications

However, not all infants present with these features. Other possible signs include:

• Microcephaly or macrocephaly
• Seizures
• Developmental delay
• Hepatosplenomegaly
• Jaundice
• Rash or petechiae
• Anaemia or thrombocytopenia

In some infants, infection is only detected later when they develop visual problems from retinal lesions, hearing loss, or learning difficulties.

Diagnosis

Diagnosis can either occur before or after birth. 

• Prenatal diagnosis involves taking blood from the mother to detect a new infection during pregnancy. This is followed by amniotic fluid testing for parasite DNA using PCR if fetal infection is suspected.⁵ In addition, an ultrasound can be used, which may reveal signs such as ventriculomegaly, intracranial calcifications (calcium deposits in the brain), or growth restriction. 
• Postnatal diagnosis relies on taking blood from the infant to detect the presence of antibodies, which can indicate active infection.⁶
• Neuroimaging techniques, such as CT or MRI scans, can be used to identify brain malformations.
• Ophthalmological examination can be carried out to detect retinal lesions.

Management and treatment

Treatment aims to limit parasite replication, reduce inflammation, and prevent progression of tissue damage.

• If maternal infection is diagnosed without evidence of fetal involvement, spiramycin is used to reduce transmission risk.
• If fetal infection is confirmed, a combination of pyrimethamine, sulfadiazine, and folinic acid is given⁷
• Anticonvulsants for seizure control
• Physiotherapy for motor impairment
• Low-vision support and hearing aids
   

Long-term outcomes

Despite advances in diagnosis and treatment, congenital toxoplasmosis remains a leading cause of preventable childhood blindness and neurological disability in some regions.

• Ocular outcomes, such as Chorioretinitis, are the most common long-term complications⁸
• Neurological outcomes such as hydrocephalus, seizures, cerebral palsy, and cognitive impairment may occur, particularly in untreated or late-treated cases. 
• Hearing loss
• Educational and developmental impacts such as learning difficulties, behavioural problems, and speech delays can emerge in later childhood

Complications

Complications of congenital toxoplasmosis can be severe and lifelong, such as:

• Blindness from recurrent retinal damage
• Severe epilepsy 
• Hydrocephalus 
• Profound developmental disability 
• Psychosocial challenges for both the child and family due to chronic health needs

Prevention

Preventing congenital toxoplasmosis relies on interrupting maternal exposure to T. gondii:

• Avoid eating undercooked or raw meat
• Wash fruits and vegetables thoroughly before eating
• Wear gloves when gardening or handling soil
• Pregnant women should avoid cleaning cat litter; if unavoidable, wear gloves and wash hands afterwards
• Drink only treated or boiled water in areas with uncertain water safety
• In high-prevalence countries, routine prenatal screening allows early detection and intervention

FAQ’s

How common is congenital toxoplasmosis?

Worldwide rates vary widely between countries, ranging from less than 1% to over 90% with lower rates in Europe and higher rates in South America and Africa.²

Can a baby be healthy at birth and still develop complications later?

Yes, because many infected infants appear normal initially but can develop serious eye or neurological problems months or years later.

Is congenital toxoplasmosis treatable?

By providing Prompt antiparasitic treatment, this can prevent or limit long-term damage, but early diagnosis is crucial.

How can infection be prevented during pregnancy?

Following safe food-handling practices, washing food thoroughly, avoiding undercooked meat, and limiting exposure to cat faeces can all significantly reduce the risk.

Summary

Congenital toxoplasmosis is a parasitic infection passed from mother to baby during pregnancy. While many infants show no signs at birth, this condition can cause serious, irreversible complications, for example, brain damage, vision loss, and seizures. The risk of transmission increases as pregnancy progresses, but infections in early pregnancy are usually the most severe.

The impact of the disease is not evenly spread across the world. For example, warmer, humid climates allow the parasite to survive more easily, allowing infections to be more common in some regions. In areas with good food safety, sanitation, and healthcare, the risk is lower. Diagnosis of this condition can be made both before birth and after birth. 

Drugs such as spiramycin can help reduce transmission from mother to fetus. Combinations of pyrimethamine, sulfadiazine, and folinic acid are used when the fetus or infant is infected. 

The most common long-term problem is eye disease,  particularly chorioretinitis, which can lead to vision loss. Other outcomes include hearing loss, epilepsy, and developmental disabilities.