Toxoplasmosis
How can toxoplasmosis be prevented? Information on causes, symptoms, treatments, and risks associated with this infection.
Symptoms and causes
Toxoplasmosis is a parasitic infection caused by Toxoplasma gondii, which usually presents as asymptomatic or with mild symptoms. In general, it does not pose a significant health risk, but it can lead to serious complications in fetuses, newborns, and immunocompromised individuals.
Toxoplasma gondii is an obligate intracellular parasite, meaning it must reside within a host to reproduce. This microorganism uses humans, pigs, sheep, and birds as intermediate hosts for asexual reproduction. Its definitive host is the feline species—particularly domestic cats—where the parasite completes its sexual reproduction cycle.
There are two primary types of toxoplasmosis based on the mode of transmission:
- Acquired toxoplasmosis: transmitted through the consumption of contaminated water or undercooked food containing parasite eggs (oocysts) shed in cat feces.
- Congenital toxoplasmosis: transmitted vertically from mother to fetus via the placenta.
Once oocysts are ingested, they release tachyzoites within the human body, which rapidly multiply inside cells and may cause tissue damage. The immune system responds by converting them into bradyzoites, which replicate slowly and remain encysted in tissues. These latent cysts can reactivate and cause disease when immune function is compromised.
Symptoms
Toxoplasmosis symptoms vary depending on the patient’s immune status and individual characteristics:
- Immunocompetent individuals:
- Often asymptomatic
- Low-grade fever
- Fatigue
- General malaise
- Headache
- Lymphadenopathy (swollen lymph nodes)
- Immunocompromised individuals:
- Ocular toxoplasmosis: eye redness, pain, inflammation, blurred vision, diplopia, floaters, photophobia, blindness
- Cerebral toxoplasmosis: fever, headache, severe fatigue, confusion, poor coordination, muscle weakness, gait disturbances, balance issues, seizures, hemiplegia
- Pulmonary toxoplasmosis: fever, cough, chest pain, respiratory failure
- Toxoplasmosis during pregnancy: in most cases, infected pregnant women do not develop severe symptoms, but vertical transmission to the fetus can occur, though it is not common.
- First trimester: may result in spontaneous miscarriage
- Newborns: hydrocephalus, hepatosplenomegaly, cerebral malformations, ocular infection
- Infants with severe disease: rash, blindness, hearing impairment, jaundice, heart disease, seizures, motor dysfunction, cognitive disability
- Children and adolescents: recurrent ocular infections, developmental delays, poor motor coordination, learning difficulties, growth retardation, early puberty, hearing loss
Causes
Toxoplasmosis is most commonly acquired through:
- Consumption of undercooked meat from infected animals
- Ingestion of raw vegetables or contaminated water
- Direct contact with cat feces
Vertical transmission can occur when a woman becomes infected during pregnancy, passing the parasite to the fetus via the placenta.
Risk Factors
The risk of developing toxoplasmosis increases in immunosuppressed individuals, particularly in the following conditions:
- HIV/AIDS
- Certain cancers
- Immunosuppressive therapy following organ transplantation
- Long-term steroid or corticosteroid use
- Chemotherapy treatment
Complications
While most individuals with toxoplasmosis remain asymptomatic or develop mild flu-like symptoms, some may experience severe complications, such as:
- Neurological damage
- Blindness
- Hearing loss
- Congenital anomalies
- Spontaneous miscarriage
- Preterm birth
Prevention
Preventive strategies for toxoplasmosis include:
- Cooking meat to an internal temperature of ≥60°C (≥140°F) for at least 3 minutes
- Cooking poultry to an internal temperature of ≥74°C (≥165°F)
- Avoiding consumption of raw meat, seafood, or fish; if consumed, they should be previously frozen at −20°C for 2 days or −10°C for 3 days
- Thorough washing of fruits and vegetables before consumption
- Avoiding unpasteurized milk and dairy products
- Drinking only potable water
- Minimizing contact with cats, especially cat feces
- Wearing gloves when gardening or handling soil
Which Specialist Manages Toxoplasmosis?
Toxoplasmosis is initially detected by gynecologists or general practitioners. If treatment is required, it is typically managed by internal medicine specialists.
Diagnosis
The primary diagnostic method for toxoplasmosis is serological testing (blood test), which detects:
- IgM antibodies: indicating a recent or active infection
- IgG antibodies: indicating past infection and established immunity
In Spain, toxoplasmosis screening is part of routine prenatal care. If an active or recent infection is suspected, additional confirmatory tests are performed in specialized laboratories. These may include histological analysis or amniotic fluid testing.
For suspected ocular toxoplasmosis, ophthalmologic tests are performed to assess retinal or chorioretinal lesions. Cerebral toxoplasmosis is evaluated using CT or MRI of the brain, and sometimes lumbar puncture.
Treatment
Treatment for toxoplasmosis depends on:
- The severity of infection
- The immune status of the patient
- Whether the infection occurs during pregnancy
Pharmacological therapy includes:
- Pyrimethamine + sulfadiazine: used in the acute phase to inhibit rapid parasite replication
- Spiramycin (oral, 1g every 8 hours): indicated for pregnant women with recent infection to reduce fetal transmission risk. Treatment continues throughout pregnancy
- If fetal infection is confirmed, treatment is switched to pyrimethamine + sulfadiazine + folinic acid (leucovorin) to minimize fetal tissue damage
- In immunocompetent individuals with mild acute infection, treatment is usually not required, although in more severe or immunocompromised cases, the above combinations are used. Alternatives include hydroxychloroquine derivatives or azithromycin
- Pyrimethamine is teratogenic and contraindicated in the first trimester. Frequent hematological monitoring is necessary due to the risk of bone marrow suppression
Additional treatments:
- Leucovorin (folinic acid): prescribed to counteract folate inhibition caused by pyrimethamine, especially during pregnancy
- Hydroxyquinoline derivatives or azithromycin: used when first-line drugs are contraindicated or ineffective; these are also effective against tissue cysts
Dosage and duration of treatment depend on disease severity and the patient's overall health status.
Newborns of infected mothers require testing to confirm congenital toxoplasmosis and ongoing clinical monitoring.
