Toxoplasmosis (tok-so-plaz-MO-sis), often called toxo, is an infection caused by the Toxoplasma gondii parasite that animals can transmit to people. It usually causes no symptoms in healthy people, but it can be serious in people with weak immune systems and in unborn babies.

What Is Toxoplasmosis?

Toxoplasmosis is a disease caused by the microscopic parasite * Toxoplasma gondii. This parasite lives in the soil and can infect humans and many species of animals. It is particularly common in cats, and the parasite's eggs pass from their bodies in their feces (FEE-seez, or bowel movements). Touching dirty litter from a cat's litter box is one common way that people contract the parasite. The eggs can stick to a person's hands and may eventually end up in the mouth, where the person can inadvertently swallow them. People also become infected by accidentally eating contaminated soil or by eating raw or undercooked meat, especially pork, lamb, and venison, containing the parasite's cysts * . Thorough cooking kills the parasite.

In addition, pregnant women can pass the disease to their unborn babies, leading to congenital (present at birth) toxoplasmosis, a condition that can range from mild to severe, and may involve developmental problems and intellectual disability, seizures * , and vision problems.

In rare cases, blood transfusions * , organ transplants, and laboratory accidents can also cause toxoplasmosis.

Toxoplasmosis is a life-long infection, although usually it is latent (inactive). Most people with toxoplasmosis have no symptoms or symptoms that are very mild. The disease can be life-threatening, however, for people with weakened immune systems * and for babies born with the disease. Toxoplasmosis may also cause miscarriage (the end of a pregnancy before a live birth) or stillbirth (the birth of a dead fetus).

How Common Is Toxoplasmosis?

The Centers for Disease Control and prevention estimates that T. gondii infects more than 60 million Americans, but cases of actual disease are much less common. Most people who carry the parasite have no symptoms of illness.

What Are the Symptoms of Toxoplasmosis?

Most people with toxoplasmosis, including pregnant women, have no symptoms. When symptoms do appear, they usually appear within 10 days of exposure, and they vary with the person's age and the response of his or her immune system. Children with toxoplasmosis fall into three groups:

* or cancer: These children may have severe infections that attack the central nervous system, brain, lungs, and heart. Symptoms may include fever, seizures, headache, psychosis (severe mental disturbance), and problems in vision, speech, movement, or thinking.

For most people who get toxoplasmosis after birth, symptoms may include:

For people with weakened immune systems (especially those with AIDS), toxoplasmosis can cause major infections of the brain or, less commonly, the lungs or heart. Severe disease can be fatal.

CT scan of the brain showing asbcess (yellow) and swelling caused by toxoplasmosis. For people with weakened immune systems, toxoplamosis can cause infections in the brain as well as the lungs or heart.

CT scan of the brain showing asbcess (yellow) and swelling caused by toxoplasmosis. For people with weakened immune systems, toxoplamosis can cause infections in the brain as well as the lungs or heart.
Scott Camazine/Science Source.

How Is Toxoplasmosis Diagnosed?

If toxoplasmosis is suspected, the doctor draws a blood sample and tests it for evidence of the parasite. For people who have weakened immune systems and are therefore more likely to develop a severe infection, a doctor may order a magnetic resonance imaging * (MRI) scan, a computed tomography * (CT) scan of the head, or rarely, a brain biopsy (removing a small sample of brain tissue to examine) to look for signs of damage caused by the parasite.

The doctor may also suggest a visit to an ophthalmologist for an eye exam, which may include the use of a special lamp called a slit lamp to check for signs of the disease in the eyes. These signs may include reduced, hazy, or blurred vision; pain when looking into bright light; eye redness; tearing; inflammation in the back of the eye; swelling in part of the retina * ; and lesions (injuries) in the retina and/or an adjacent membrane called the chorioid. Ophthalmologists sometimes prescribe medicine to treat active disease. Occasionally, an eye doctor may find signs of a prior infection with the T. gondii parasite during a routine eye exam, even though the patient never experienced or noticed any symptoms. This is not a cause for alarm, but pregnant women and those with weakened immune systems should discuss the findings with their regular doctor to determine whether they should take any additional precautions to prevent repeat infection.

What Is the Treatment for Toxoplasmosis?

People who have symptoms from toxoplasmosis but are otherwise healthy do not need any treatment, and their symptoms will likely only last a few days. Doctors treat pregnant women, newborns with the congenital infection, and people with weak immune systems with medication. Patients with AIDS often continue taking the medicine even after the infection clears up to keep it from returning. In newborns and patients with unhealthy immune systems, the illness can last for weeks or months, and it can cause permanent disability.

How Is Toxoplasmosis Prevented?

Toxoplasmosis can be prevented by careful attention to hygiene and sanitation. Preventive steps include:

In addition, pregnant women and people whose immune systems are weak can take additional precautionary measures, including being tested for the parasite. This allows the doctor to discover the infection and begin treatment even if the individual does not have any symptoms. Even if people in these groups do not have an infection, they should be especially careful to avoid contact with soil, uncooked meat, and strange or stray cats. In addition, they should keep their own cats indoors and on a diet of canned or dried cat food because cats can pick up the parasite from eating raw meat.

See also AIDS and HIV Infection • Cancer: Overview • Parasitic Diseases: Overview • Pregnancy • Zoonoses: Overview


Books and Articles

Hamblin, James. “Do Cats Control My Mind?” The Atlantic, December 5, 2013. (accessed November 17, 2015).

Hokelek, Murat. “Toxoplasmosis.” Medscape, September 8, 2014. (accessed November 17, 2015).


HIV InSite. “Toxoplasmosis and HIV.” University of California, San Francisco. (accessed November 17, 2015).

NHS Choices. “Toxoplasmosis.” National Health Service. (accessed November 17, 2015).

Tommy's: Your Online Midwife. “Toxoplasmosis and Pregnancy.” (accessed November 17, 2015).


American Academy of Family Physicians. PO Box 11210, Shawnee Mission, KS 66207-1210. Toll-free: 800-274-2237. Website: (accessed November 17, 2015).

Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30329-4027. Toll-free: 888-674-6854. Website: (accessed November 17, 2015).

March of Dimes. 1275 Mamaroneck Ave., White Plains, NY 10605. Telephone: 914-997-4488. Website: (accessed November 17, 2015).

* parasite (PAIR-uh-site) is an organism such as a protozoan (one-celled animals), worm, or insect that must live on or inside a human or other organism to survive.

* cysts (SISTS) are shell-like enclosures that contain small organisms in a resting stage.

* seizures (SEE-zhurs) are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.

* blood transfusions (trans-FYOOzhunz) are procedures in which blood or certain parts of blood (such as specific cells) are given to a person who needs them due to illness or blood loss.

* immune system (im-YOON SIStem) is the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.

* AIDS, or acquired immunodeficiency (ih-myoo-no-dih-FIH-shensee) syndrome, is an infection that severely weakens the immune system; it is caused by the human immunodeficiency virus (HIV).

* lymph nodes (LIMF) are small, bean-shaped masses of tissue containing immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.

* magnetic resonance imaging (MRI) is a diagnostic procedure that uses magnetic waves, instead of x-rays, to scan the body and produce detailed pictures of the body's structures.

* computed tomography (komPYOO-ted toe-MAH-gruh-fee), or CT, is a technique in which a machine takes many x-rays of the body to create a threedimensional picture. Formerly called computerized axial tomography (CAT).

* retina (RET-i-nuh) is the tissue that forms the inner surface of the back of the eyeballs; it receives the light that enters the eye and transmits it through the optic nerves to the brain to produce visual images.

  This information is not a tool for self-diagnosis or a substitute for professional care.