What Is Toxoplasmosis? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Toxoplasmosis is an infectious disease caused by the parasite Toxoplasma gondii.

Although cats and their feline relatives are the only hosts in which T. gondii reproduces, the parasite is found in humans and numerous other animals, including rodents, birds, pigs, and sheep. (1)

Cats play a vital role in T. gondii’s life cycle and the spread of toxoplasmosis to people.

A cat becomes infected with T. gondii after eating birds or small mammals infected with the parasite. (2)

The parasites then reproduce in the cat’s small intestine and form oocysts, which are thick-walled cysts containing zygotes.

The cat eventually sheds the oocysts in its feces. “Cats usually only shed oocysts in their feces once during their lifetime, with a few exceptions, and many infected with T. gondii may never shed oocysts at all,” explains Heather Stockdale Walden, PhD, an associate professor of parasitology at the University of Florida College of Veterinary Medicine in Gainesville.

A single cat can shed millions of oocysts for up to three weeks after infection.

Most infected cats show no signs or symptoms, Dr. Walden says, but a feline that is shedding oocysts can infect its litter box. Humans can become infected by accidentally ingesting oocysts after cleaning the litter box or after touching anything that has come in contact with the cat’s feces that contain T. gondii. Other animals become infected when they ingest soil, water, or plants contaminated with oocysts. (3)

Oftentimes, people infected with T. Gondii are not even aware they have it.

“Most people don’t have symptoms with toxoplasmosis or have mild symptoms like fever and muscle aches, as with any infection,” says Amy Edwards, MD, a pediatric infectious disease specialist at UH Rainbow Babies and Children’s Hospital in Cleveland. “It’s usually pretty nonspecific.”

Other symptoms may include: (4)

• Enlarged and tender lymph nodes in the head and neck
• Headache
• Sore throat

If you have a weakened immune system, such as from HIV or cancer, you may experience more severe symptoms, such as:

• Confusion
• Fever and headache
• Blurred vision
• Seizures
• Nausea
• Poor coordination

You can get toxoplasmosis by ingesting food or drink contaminated with T. gondii. This can happen by: (3)

• Eating uncooked or raw meat that’s infected with the parasite, particularly venison, pork, or lamb
• Drinking water or another liquid that’s been contaminated with the parasite
• Eating food that’s been contaminated with the parasite through direct contact or indirectly through knives, utensils, or cutting boards
• Accidentally ingesting tiny particles of infected meat after handling it and failing to wash your hands
• Eating fruit or vegetables that have been in contact with soil or water contaminated with the parasite and have not been washed, peeled, or cooked

You can also get toxoplasmosis by swallowing particles of oocyst-laden cat feces, such as if you touch your mouth after cleaning or changing your cat’s litter, handle objects that have come into contact with cat feces, or garden without gloves.

In very rare cases, you can get the disease through a blood transfusion or an organ transplant.

Toxoplasmosis is typically diagnosed by a blood test that checks for antibodies to the parasite.

If a woman tests positive during pregnancy, a doctor will check to see if the baby is infected. This is done by testing fluid from the amniotic sac for evidence of toxoplasmosis. Ultrasounds can also detect certain signs of infection, including fluid buildup in the brain. (5)

For most people, toxoplasmosis will go away on its own, Dr. Edwards says. Eventually, after a few weeks or months, your immune system will fight off the disease.

Those requiring treatment will be put on medication that can take weeks or even months to clear the infection, Edwards says.

People with healthy immune systems usually don’t require treatment, but a combination of antibiotics and antimalarial drugs may help with symptoms.

Drugs that are commonly used for healthy (nonpregnant) adults who are infected include pyrimethamine and sulfadiazine, plus folinic acid (leucovorin). (5) Another potential treatment is trimethoprim-sulfamethoxazole (Bactrim).

People with weakened immune systems, such as those living with HIV, may also be treated with these drugs until their condition improves, although some will require lifelong treatment at a lower dose or with alternative drugs. (6)

Other drug combinations may also be used in these situations, such as pyrimethamine plus clindamycin (Cleocin Hcl).

Pregnant women in their first or early second trimester are commonly treated with spiramycin, while those in their late second or third trimester are commonly treated with pyrimethamine and sulfadiazine plus leucovorin.

Newborns are generally treated with pyrimethamine and sulfadiazine plus leucovorin for their first year of life. These are general guidelines and would be customized to each patient’s specific needs and risk factors. (5)

Prevention of Toxoplasmosis

To prevent toxoplasmosis infection from food, the CDC recommends the following guidelines:

Use a food thermometer to assure meat and poultry are cooked to safe temperatures.

Whole cuts of meat should be cooked to an internal temperature of at least 145 degrees F. Ground meat should be cooked to at least 160 degrees F. And poultry should be cooked to at least 165 degrees F.

Peel or thoroughly wash fruit and vegetables before consuming.

Thoroughly wash cutting boards, dishes, utensils, and surfaces that have come in contact with raw meat or poultry, seafood, and unwashed produce.

Do not consume unpasteurized goat milk.

Avoid eating raw or undercooked oysters, mussels, and clams.

To prevent infection from cats, cat owners should change the litter box daily, avoid feeding their pet raw or undercooked meat, and keep their cat indoors to reduce the risk of infection. Pregnant women should not clean the litter box if possible, or if there is no one else able to, they should wear disposable gloves and wash their hands after.

Everyone should avoid drinking untreated water and wear gloves while gardening or when coming into contact with soil or sand. Remember to always wash your hands afterward, as there might be contamination with cat feces in these areas. (7)

If you get toxoplasmosis while pregnant, you may pass it on to your unborn baby (congenital toxoplasmosis), even if you don’t experience any symptoms.

But if you had the disease before becoming pregnant, your child is not at risk for toxoplasmosis — your immune system confers protection.

It’s sometimes recommended to wait at least six months after an infection before becoming pregnant.

“Toxoplasmosis can be transmitted across the placenta to the unborn child when a pregnant woman acquires the infection for the first time while she is pregnant and not immune,” explains Rima McLeod, MD, medical director of the University of Chicago Medicine Toxoplasmosis Center. “The unborn child is immunologically immature, and so the infection can be particularly harmful to their eyes, brain, and general well-being. That damage can be recurring and manifested lifelong.”

Toxoplasmosis during pregnancy can also result in miscarriage, stillbirth, or a child born with signs of the disease, such as an abnormal head size.

Additionally, it’s possible to develop ocular (eye) disease from T. gondii, usually if you were born with toxoplasmosis. The disease can cause inflammatory retinal lesions and scarring, resulting in eye pain, light sensitivity, tearing, and blurred vision. (8)

Some research suggests that T. gondii can affect personality and behavior, including causing neuroticism, schizophrenia, depression, and suicidal tendencies. A 2015 study, for example, concluded that cat ownership in childhood is significantly more common in families in which the child later becomes “seriously mentally ill.” The mechanism, researchers hypothesize, could be toxoplasmosis. (9)

The theory, though, is that when the parasite gets into the brain, “depending on where it lodges, it can cause chronic inflammation. This can slowly damage the brain in that area, leading to neurological or psychological problems depending on the area involved,” Edwards explains.

However, in the aforementioned study, the researchers observed only a correlative link between childhood cat ownership and future mental illness; more studies are needed before researchers can definitively say that one causes the other. What’s more, a 2016 study points to flaws in previous research and concludes that there is little scientific evidence that T. gondii is related to increased risk of psychiatric disorder. (10)

An estimated 40 million people in the United States may be infected with T. gondii, but most people don’t have symptoms, as the immune system usually keeps the parasite from causing sickness. (11)

What’s more, up to 60 percent of some populations across the globe are infected by the parasite. (3)

Favorite Organizations for Info on Toxoplasmosis

American Veterinary Medical Association (AVMA)

The American Veterinary Medical Association is the nation’s leading advocacy organization for veterinarians. Stay informed on the most up-to-date info on how toxoplasmosis affects cats and tips on how you can help keep your pet and family safe.

Companion Animal Parasite Council (CAPC)

The Companion Animal Parasite Council is an independent council of veterinarians, veterinary parasitologists, and other animal healthcare professionals established to create guidelines for the optimal control of parasites that threaten the health of pets and their owners. In addition to information on toxoplasmosis, CAPC offers helpful, bookmarkable resources on what to do if your pet becomes infected by other parasites, including ticks, fleas, tapeworms, and ear mites.