Toxoplasmosis

What toxoplasmosis is

Toxoplasma gondii is a single-celled parasite. Cats are its main host: the parasite reproduces in the cat's gut and is shed in feces as tiny eggs (oocysts) for 1 to 3 weeks after a cat is first infected. Oocysts become infectious after 1 to 5 days in the environment and survive in soil and water for many months.

Other animals, including livestock, become infected and carry parasite cysts in their muscle. Humans become infected by eating these cysts in undercooked meat or by swallowing oocysts from soil, cat litter or contaminated food and water.

After infection, the immune system controls the parasite, but dormant cysts remain in the brain, muscles and eyes for life. They can reactivate if the immune system later becomes weak.

How toxoplasmosis spreads

• Food: undercooked or raw pork, lamb, venison or beef; cured meats; raw shellfish; unpasteurized goat's milk
• Soil and produce: gardening without gloves, unwashed fruit and vegetables
• Cats: cleaning litter boxes, especially of outdoor cats or kittens that hunt
• Water: untreated water
• Mother to baby: when a mother is first infected during or just before pregnancy
• Organ transplant or blood transfusion (rare)

It does not spread from person to person through casual contact. You are very unlikely to catch it from petting a cat.

Toxoplasmosis symptoms

Healthy adults and children

Most people (about 8 or 9 in 10) have no symptoms. Others notice:

• swollen lymph nodes, especially in the neck, lasting weeks
• muscle aches and fatigue
• fever and headache
• sometimes a sore throat

The illness can resemble mononucleosis and usually settles on its own within weeks to months.

Eye (ocular) toxoplasmosis

The parasite can infect the retina, causing chorioretinitis: blurred vision, floaters, eye pain and light sensitivity, usually in one eye. It is a leading cause of infectious posterior uveitis worldwide and tends to recur from old scars.

People with weakened immunity

In people with advanced HIV (CD4 count under 100), transplant recipients and those on chemotherapy, dormant cysts can reactivate, causing:

• brain toxoplasmosis (toxoplasmic encephalitis) with headache, confusion, fever, seizures and weakness
• lung, eye or widespread infection

Toxoplasmosis in pregnancy

Toxoplasmosis is mostly a concern if you are infected for the first time during pregnancy or in the few months before. If you were infected long before pregnancy, the risk to the baby is very low unless your immune system is suppressed.

• The chance of the parasite crossing the placenta increases as pregnancy progresses.
• Infections early in pregnancy are less likely to pass on but more likely to cause serious harm.
• Many infected babies look healthy at birth but can develop eye problems or learning difficulties later.

Congenital toxoplasmosis can cause:

• miscarriage or stillbirth
• eye damage (chorioretinitis), which may appear years later
• hydrocephalus (fluid on the brain), brain calcifications and seizures
• an enlarged liver and spleen, jaundice and rash
• hearing loss and developmental delay

It is one of the classic congenital infections, along with cytomegalovirus, rubella and syphilis.

Do pregnant people need to give up their cat?

No. Indoor cats fed commercial food are unlikely to be infected. Have someone else change the litter if possible. If you must do it, wear gloves, change it daily (before oocysts become infectious) and wash your hands afterward. Do not adopt or handle stray cats or new kittens during pregnancy.

Testing

• Toxoplasma IgG antibodies: show past infection; positive IgG before pregnancy means you are immune.
• IgM antibodies: suggest a recent infection but can persist for months or a year or more, or be falsely positive, so results should be confirmed at a reference laboratory.
• IgG avidity test: helps date the infection. High avidity means infection more than about 3 to 5 months ago.
• PCR of amniotic fluid (amniocentesis) to check if the baby is infected, along with detailed ultrasound.
• Eye exam by an ophthalmologist for eye symptoms.
• Brain MRI or CT for suspected brain toxoplasmosis.

Routine screening in pregnancy is not standard in the US but is common in France, Austria and some other countries.

Treatment

• Healthy, non-pregnant people: usually no treatment, as symptoms resolve on their own. Treatment is used for severe or persistent symptoms.
• Pregnancy: spiramycin for infection acquired early in pregnancy to reduce transmission to the baby. If the baby is infected or infection occurs later in pregnancy, pyrimethamine, sulfadiazine and leucovorin (folinic acid) are used. Treatment is directed by a maternal-fetal medicine specialist.
• Infected babies: pyrimethamine, sulfadiazine and leucovorin, usually for 12 months, which improves eye and developmental outcomes.
• Eye toxoplasmosis: antiparasitic drugs (such as trimethoprim-sulfamethoxazole or pyrimethamine combinations), often with steroids when vision is threatened.
• Weakened immunity: pyrimethamine, sulfadiazine and leucovorin for at least 6 weeks, followed by maintenance therapy. People with HIV and a CD4 count under 100 who test IgG positive take trimethoprim-sulfamethoxazole to prevent it, plus HIV treatment to restore immunity.

Prevention

• Cook meat to safe temperatures: whole cuts to 145 °F (63 °C) with a 3-minute rest, ground meat to 160 °F (71 °C), poultry to 165 °F (74 °C).
• Freezing meat for several days at sub-zero temperatures reduces the risk.
• Wash cutting boards, knives, hands and counters after handling raw meat.
• Wash or peel fruit and vegetables.
• Wear gloves when gardening and wash hands afterward.
• Change cat litter daily, with gloves, or have someone else do it.
• Keep cats indoors and feed them commercial food, not raw meat.
• Avoid untreated water and unpasteurized goat's milk.
• Cover children's sandboxes.

Frequently asked questions

What are the symptoms of toxoplasmosis?

Most people have no symptoms. Some develop swollen lymph nodes, muscle aches, fatigue, fever and headache lasting weeks. Eye infection causes blurred vision and floaters. In people with weakened immunity it can cause confusion, seizures and other brain symptoms.

Can you get toxoplasmosis from cats?

Yes, but it is less common than catching it from undercooked meat or soil. Infected cats shed the parasite in feces for only a few weeks, usually when young. Changing litter daily with gloves and washing hands makes the risk very small.

Is toxoplasmosis dangerous in pregnancy?

It can be, if you catch it for the first time during or shortly before pregnancy. It can cause miscarriage or damage to the baby's eyes and brain. Treatment during pregnancy reduces risks. Simple food, garden and litter precautions prevent most infections.

Does toxoplasmosis go away?

The symptoms usually go away on their own, but the parasite stays dormant in the body for life. In healthy people this causes no problems and gives lasting immunity. It can reactivate if the immune system becomes severely weakened.

How is toxoplasmosis diagnosed?

With blood tests for toxoplasma antibodies (IgG and IgM), sometimes with an avidity test to estimate when infection happened. Eye infections are diagnosed by an eye exam, and brain infection by MRI and tests. In pregnancy, amniotic fluid testing can show if the baby is infected.