Toxoplasmosis is a zoonotic disease caused by Toxoplasma gondii. This pathogen is widely distributed in nature, with almost all mammals and certain bird species serving as intermediate hosts, and felines acting as the only definitive host. The seropositivity rate for specific antibodies against T. gondii in infected individuals ranges from 25%–50%, while the infection rate among pregnant women is between 6.25% and 32.9%, showing an upward trend over the years. Reports indicate the highest infection rates in regions such as Europe, Central America, Brazil, and Central Africa. In France, the prevalence among pregnant women decreased from 80% in the 1960s to 31% in 2016.
Most adult infections are subclinical. Congenital toxoplasmosis occurs as a result of transplacental transmission, primarily from maternal primary infections, whereas congenital infection from maternal chronic infection is rare. The transplacental transmission rate is approximately 40%, increasing with gestational age, though the severity of fetal infection decreases as pregnancy advances. Toxoplasmosis is a significant cause of congenital central nervous system (CNS) malformations and neurodevelopmental disorders.
Clinical Manifestations
The central nervous system and eyes are the primary sites of damage. Chorioretinitis, hydrocephalus, and cerebral calcifications form the classic triad of congenital toxoplasmosis. Two-thirds of affected infants exhibit no obvious symptoms at birth, though one-third have subclinical changes. Untreated cases may gradually manifest symptoms weeks, months, or even years after birth. The severity of symptoms depends on the stage of pregnancy during which the intrauterine infection occurred. Severe effects, including miscarriage, preterm delivery, or stillbirth, are more likely when infection occurs in early pregnancy. Infections in the mid-to-late stages often result in subclinical infection or delayed clinical manifestations after birth.
The main clinical manifestations include:
- Systemic Symptoms: Jaundice, hepatosplenomegaly, petechiae, rash, fever or temperature instability, pneumonia, myocarditis, nephritis, and lymphadenopathy.
- Central Nervous System (CNS): Symptoms and signs of meningoencephalitis, such as bulging fontanelle, seizures, opisthotonus, and coma, may present. Cerebrospinal fluid often shows abnormalities, including increased lymphocytes, elevated protein levels, and decreased glucose levels. Head CT scans may reveal obstructive hydrocephalus or cortical calcifications. Hydrocephalus can occasionally be the sole manifestation of congenital toxoplasmosis, potentially appearing at birth or developing postnatally.
- Ocular Lesions: Chorioretinitis is the most common manifestation, affecting one or both eyes. Other findings include microphthalmia and anophthalmia. Vision impairment due to ocular involvement is a common outcome. Only 10% of infants display overt symptoms at birth, with approximately 10% dying. Among survivors, most experience neurological sequelae such as intellectual developmental delays, seizures, cerebral palsy, and vision impairments.
- Other Features: Preterm birth and intrauterine growth restriction (IUGR). Among symptomatic cases, 30%–70% exhibit cerebral calcifications, which may increase in size and number without treatment. Treatment results in the reduction or disappearance of calcifications in approximately 75% of cases by one year of age.
Diagnosis
Diagnosis is based on maternal infection history, clinical manifestations, and laboratory findings. Definitive confirmation relies on pathogen detection or serological testing.
- Pathogen Detection: Direct smears or tissue cultures from blood, bodily fluids, or lymph nodes can be used to identify the pathogen. However, this method is complex, and the positive detection rate is low.
- Antibody Testing: ELISA is used to detect T. gondii-specific IgG and IgM antibodies with high sensitivity and specificity.
- Toxoplasma Circulating Antigen (TCAg): TCAg, a metabolic product of tachyzoites, can be detected in serum or bodily fluids and is valuable for diagnosing acute infections.
- Polymerase Chain Reaction (PCR): PCR testing of maternal blood or amniotic fluid detects T. gondii DNA. Detection of T. gondii DNA in fetal amniotic fluid suggests intrauterine infection.
Treatment
Sulfadiazine is administered at a daily dose of 100 mg/kg, divided into four oral doses over a course lasting 4–6 weeks.
Pyrimethamine is given at 1 mg/kg every 12 hours for the first 2–4 days, then halved for the remainder of the 4–6 week course. Treatment consists of 3–4 cycles, spaced one month apart. Combined therapy with sulfadiazine and pyrimethamine is recommended until one year of age. These medications may cause bone marrow suppression and folate deficiency, necessitating regular blood monitoring and concurrent administration of folic acid (5 mg, three times daily).
Spiramycin concentrates in placental tissues and does not harm the fetus, making it suitable for use in pregnant women and neonates with congenital toxoplasmosis. The adult dose is 2–4 g per day, while children receive 100 mg/kg daily, divided into 2–4 doses.
Corticosteroids are indicated for cases with chorioretinitis or cerebrospinal fluid protein levels ≥10 g/L, with prednisone dosed at 0.5 mg/kg twice daily.
Serological screening in pregnant women aids in early detection. Intrauterine infection during the first trimester of pregnancy warrants termination, while infections in the second or third trimester require treatment.
Prognosis
Infections acquired during the early and mid-pregnancy stages result in perinatal or neonatal mortality rates of 35% and 7%, respectively. Among infants with congenital toxoplasmosis, the mortality rate reaches 12%. Congenital infections markedly increase the risk of ocular lesions, neurodevelopmental delays, and hearing impairment. Intellectual disability occurs in 87% of cases, seizures in 82%, spasticity or cerebral palsy in 71%, and hearing loss in 15%. Long-term follow-up data indicate that 80%–90% of neonates with subclinical infections develop ocular or neurological complications by adulthood. Infections occurring before 20 weeks of gestation are grounds for pregnancy termination.