Toxoplasmosis

Date Updated: 10/13/2020

Overview

Toxoplasmosis (tok-so-plaz-MOE-sis) is a disease that results from infection with the Toxoplasma gondii parasite, one of the world's most common parasites. Infection usually occurs by eating undercooked contaminated meat, exposure from infected cat feces, or mother-to-child transmission during pregnancy.

Toxoplasmosis may cause flu-like symptoms in some people, but most people affected never develop signs and symptoms. For infants born to infected mothers and for people with weakened immune systems, toxoplasmosis may cause serious complications.

If you're generally healthy, not pregnant, and have been diagnosed with toxoplasmosis, you probably won't need any treatment other than conservative management. If you're pregnant or have lowered immunity, you may need medical management to avoid severe complications. The best approach, though, is prevention.

Symptoms

Most healthy people who are infected with toxoplasmosis have no signs or symptoms and aren't aware that they're infected. Some people, however, develop signs and symptoms similar to those of the flu, including:

Body aches
Swollen lymph nodes
Headache
Fever
Fatigue

In people with weakened immune systems

If you have HIV/AIDS, are receiving chemotherapy or have recently had an organ transplant, a previous toxoplasma infection may reactivate. In that case, you may develop more-severe signs and symptoms of infection, including:

Headache
Confusion
Poor coordination
Seizures
Lung problems that may resemble tuberculosis or Pneumocystis jiroveci pneumonia, a common opportunistic infection that occurs in people with AIDS
Blurred vision caused by severe inflammation of your retina (ocular toxoplasmosis)

In babies

If you become infected for the first time just before or during your pregnancy, you can pass the infection to your baby (congenital toxoplasmosis), even if you don't have signs and symptoms yourself.

Your baby is most at risk of contracting toxoplasmosis if you become infected in the third trimester and least at risk if you become infected during the first trimester. On the other hand, the earlier in your pregnancy the infection occurs, the more serious the outcome for your baby.

Many early infections end in stillbirth or miscarriage. Infants who survive are likely to be born with serious problems, such as:

Seizures
An enlarged liver and spleen
Yellowing of the skin and whites of the eyes (jaundice)
Severe eye infections

Only a small number of babies who have toxoplasmosis show signs of the disease at birth. Often, infants who are infected don't develop signs — which may include hearing loss, mental disability or serious eye infections — until their teens or later.

When to see a doctor

If you are living with HIV or AIDS or are pregnant or thinking of becoming pregnant, talk to your doctor about being tested if you think you may have been exposed to toxoplasmosis.

The signs and symptoms of severe toxoplasmosis — blurred vision, confusion, loss of coordination — require immediate medical care, particularly if your immune system has been weakened.

Causes

Toxoplasma gondii (T. gondii) is a single-celled parasitic organism that can infect most animals and birds. Because T. gondii infectious organisms are excreted only in cat feces, wild and domestic cats are the parasite's ultimate host.

Although you can't "catch" toxoplasmosis from an infected child or adult, you can become infected if you:

Come into contact with cat feces that contain the parasite. You may accidentally ingest the parasites if you touch your mouth after gardening, cleaning a litter box or touching anything that has come in contact with infected cat feces. Cats who hunt or who are fed raw meat are most likely to harbor T. gondii.
Eat or drink contaminated food or water. Lamb, pork and venison are especially likely to be infected with T. gondii. Occasionally, unpasteurized dairy products also may contain the parasite. Water contaminated with T. gondii isn't common in the United States.
Use contaminated knives, cutting boards or other utensils. Kitchen utensils that come into contact with raw meat can harbor the parasites unless the utensils are washed thoroughly in hot, soapy water.
Eat unwashed fruits and vegetables. The surface of fruits and vegetables may contain the parasite. To be safe, thoroughly wash and peel all produce, especially any you eat raw.
Receive an infected organ transplant or transfused blood. In rare cases, toxoplasmosis can be transmitted through an organ transplant or blood transfusion.

When a person becomes infected with T. gondii, the parasite forms cysts that can affect almost any part of the body — often your brain and muscle tissue of different organs, including the heart.

If you're generally healthy, your immune system keeps the parasites in check. They remain in your body in an inactive state, providing you with lifelong immunity so that you can't become infected with the parasite again. But if your immune system is weakened by disease or certain medications, the infection can be reactivated, leading to serious complications.

Risk factors

Anyone can become infected with toxoplasmosis. The parasite is found throughout the world.

You're at risk of serious health problems from toxoplasmosis infection if:

You have HIV/AIDS. Many people with HIV/AIDS also have toxoplasmosis, either a recent infection or an old infection that has reactivated.
You're undergoing chemotherapy. Chemotherapy affects your immune system, making it difficult for your body to fight even minor infections.
You take steroids or other immunosuppressant drugs. Medications used to treat certain nonmalignant conditions suppress your immune system and make you more likely to develop complications of toxoplasmosis.

Complications

If you have a normal immune system, you're not likely to experience complications of toxoplasmosis, although otherwise healthy people sometimes develop eye infections. Untreated, these infections can lead to blindness.

But if your immune system is weakened, especially as a result of HIV/AIDS, toxoplasmosis can lead to seizures and life-threatening illnesses such as encephalitis — a serious brain infection.

In people with AIDS, untreated encephalitis from toxoplasmosis is fatal. Relapse is a constant concern for people with toxoplasmosis who also have a weakened immune system.

Children with congenital toxoplasmosis may develop disabling complications, including hearing loss, mental disability and blindness.

Prevention

Certain precautions can help prevent toxoplasmosis:

Wear gloves when you garden or handle soil. Wear gloves whenever you work outdoors and wash your hands thoroughly with soap and water afterward.
Don't eat raw or undercooked meat. Meat, especially lamb, pork and beef, can harbor toxoplasma organisms. Don't taste meat before it's fully cooked. Avoid raw cured meat.
Wash kitchen utensils thoroughly. After preparing raw meat, wash cutting boards, knives and other utensils in hot, soapy water to prevent cross-contamination of other foods. Wash your hands after handling raw meat.
Wash all fruits and vegetables. Scrub fresh fruits and vegetables, especially if you plan to eat them raw. Remove peels when possible, but only after washing.
Don't drink unpasteurized milk. Unpasteurized milk and other dairy products may contain toxoplasma parasites.
Cover children's sandboxes. If you have a sandbox, cover it when your children aren't playing in it to keep cats from using it as a litter box.

For cat lovers

If you're pregnant or otherwise at risk of toxoplasmosis or its complications, take these steps to protect yourself:

Help your cat stay healthy. Keep your cat indoors and feed it dry or canned cat food, not raw meat. Cats can become infected after eating infected prey or undercooked meat that contains the parasite.
Avoid stray cats or kittens. Although all stray animals need good homes, it's best to let someone else adopt them. Most cats don't show signs of T. gondii infection, and although they can be tested for toxoplasmosis, it may take up to a month to get the results.
Have someone else clean your cat's litter box. If that's not possible, wear gloves and a face mask to change the litter. Then wash your hands well. Change the litter daily so that excreted cysts don't have time to become infectious.

Diagnosis

Most pregnant women in the United States aren't routinely screened for toxoplasmosis, and most states don't screen infants for the infection. Without specific screening, toxoplasmosis is often difficult to diagnose because signs and symptoms, when they occur, are similar to those of more common illnesses, such as the flu and mononucleosis.

Testing during pregnancy

If your doctor suspects you have the infection, you may have blood tests that check for antibodies to the parasite. Antibodies are proteins produced by your immune system in response to the presence of foreign substances, such as parasites. Because these antibody tests can be difficult to interpret, the Centers for Disease Control and Prevention recommends that all positive results be confirmed by a laboratory that specializes in diagnosing toxoplasmosis.

What test results mean

Sometimes you may be tested early in the course of the disease before your body has a chance to produce antibodies. In that case, you may have a negative result, even though you're infected. To be certain, your doctor may recommend retesting several weeks later.

In most cases, a negative toxoplasmosis test result means you've never been infected and therefore aren't immune to the disease. If you're at high risk, you can take certain precautions so that you don't become infected.

A positive result could mean that you have an active infection, or it could mean that you were once infected and are immune to the disease. Additional tests can pinpoint when the infection occurred, based on the types of antibodies in your blood. This is especially important if you're pregnant or you have HIV/AIDS.

Testing your baby

If you are pregnant and have a current toxoplasmosis infection, the next step is to determine whether your baby also is infected. Tests your doctor may recommend include:

Amniocentesis. In this procedure, which may be done safely after 15 weeks of pregnancy, your doctor uses a fine needle to remove a small amount of fluid from the fluid-filled sac that surrounds the fetus (amniotic sac). Tests are then performed on the fluid to check for evidence of toxoplasmosis. Amniocentesis carries a slight risk of miscarriage and minor complications, such as cramping, leaking fluid or irritation where the needle was inserted.
Ultrasound scan. This test uses sound waves to produce images of your baby in the womb. A detailed ultrasound can't diagnose toxoplasmosis. It can however, show whether your baby has certain signs, such as fluid buildup in the brain (hydrocephalus). However, a negative ultrasound doesn't rule out the possibility of infection. For that reason, your newborn will need an examination and follow-up blood tests during the first year of life.

Testing in severe cases

If you've developed a life-threatening illness such as encephalitis, you may need one or more imaging tests to check for lesions or cysts in your brain. These include:

Magnetic resonance imaging (MRI). This test uses a magnetic field and radio (electromagnetic) waves to create cross-sectional images of your head and brain. During the procedure, you lie inside a large, doughnut-shaped machine that contains a magnet surrounded by coils that send and receive radio waves.

In response to the radio waves, your body produces faint signals that are picked up by the coils and processed into images by a computer. MRI is noninvasive and poses minimal risks to your health.
Brain biopsy. In rare cases, especially if you don't respond to treatment, a neurosurgeon may take a small sample of brain tissue. The sample is then analyzed in a laboratory to check for toxoplasmosis cysts.

Treatment

Most healthy people don't require toxoplasmosis treatment. But if you're otherwise healthy and have signs and symptoms of acute toxoplasmosis, your doctor may prescribe the following drugs:

Pyrimethamine (Daraprim). This medication, typically used for malaria, is a folic acid antagonist. It may prevent your body from absorbing the B vitamin folate (folic acid, vitamin B-9), especially when you take high doses over a long period. For that reason, your doctor may recommend taking additional folic acid.

Other potential side effects of pyrimethamine include bone marrow suppression and liver toxicity.
Sulfadiazine. This antibiotic is used with pyrimethamine to treat toxoplasmosis.

Treating people with HIV/AIDS

If you have HIV/AIDS, the treatment of choice for toxoplasmosis is also pyrimethamine and sulfadiazine, with folinic acid (leucovorin). An alternative is pyrimethamine taken with clindamycin (Cleocin).

Treating pregnant women and babies

If you're pregnant and infected with toxoplasmosis, treatment may vary depending on where you receive medical care.

If infection occurred before the 16th week of pregnancy, you may receive the antibiotic spiramycin. Use of this drug may reduce your baby's risk of neurological problems from congenital toxoplasmosis. Spiramycin is routinely used to treat toxoplasmosis in Europe, but is still considered experimental in the United States.

If infection occurred after the 16th week of pregnancy, or if tests show that your unborn child has toxoplasmosis, you may be given pyrimethamine and sulfadiazine and folinic acid (leucovorin). Your doctor will help you determine the optimal treatment.

If your infant has toxoplasmosis or is likely to have it, treatment with pyrimethamine and sulfadiazine and folinic acid (leucovorin) is recommended. Your baby's doctor will need to monitor your baby while he or she is taking these medications.

Preparing for an appointment

You're likely to start by seeing your family doctor. If you're pregnant, you'll likely see your obstetrician, or you may be referred to a doctor who specializes in fetal health (perinatologist). In some instances, you may be referred to a doctor who specializes in infectious diseases.

Here's some information to help you get ready for your appointment.

What you can do

You may want to write a list that includes:

Descriptions of your symptoms
Information about medical problems you've had
Information about the medical problems of your parents or siblings
Medications and dietary supplements you take
Questions you want to ask the doctor

For toxoplasmosis, some basic questions to ask your doctor include:

What tests do I need?
What treatments are available, and which do you recommend?
What side effects might I expect from treatment?
I'm pregnant. What effect will this have on my baby?
I have other health problems. How can I manage them together?
Are there brochures or other printed materials I can have? What websites do you recommend?

Don't hesitate to ask other questions, as well.

What to expect from your doctor

Your doctor is likely to ask you a number of questions, such as:

When did your symptoms start?
How severe are your symptoms?
Have you recently consumed raw or undercooked meat?
Do you own or care for a cat? Who changes the litter box?
Do you wear gloves when gardening or working with soil?
Do you have conditions or take medications that affect your immune system?