Toxoplasmosis

Medically Reviewed By William C. Lloyd III, MD, FACS
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What is toxoplasmosis?

Toxoplasmosis is a parasitic infection caused by Toxoplasma gondii. This single-celled parasite lives in cats. Cats shed the eggs in their stool and contaminate soil, water, and other materials, such as litter. Other animals get toxoplasmosis from cats when they ingest the eggs. The eggs then turn into tachyzoites, which are a form of the parasite that can move. The tachyzoites invade tissues, such as the nerves and muscles. Here, they form cysts, which the immune system is able to keep dormant.

Humans can get toxoplasmosis by eating undercooked meat contaminated with cysts or by contact with egg-contaminated cat litter or stool. The parasites then form cysts in the muscles, eyes, heart or brain. In healthy people, the cysts remain dormant for the rest of their lives and do not cause problems. If the immune system becomes weak due to disease or drugs, the cysts can activate and cause symptoms.

Toxoplasmosis is extremely common in the United States. According to the CDC (Centers for Disease Control and Prevention), more than 40 million Americans have the infection. However, most do not know it because it does not cause symptoms in healthy people. When toxoplasmosis symptoms occur, they are flu-like in nature.

In most cases, healthy people with toxoplasmosis do not require treatment. In fact, most people do not know they are infected. People at risk of complications need toxoplasmosis treatment with antiparasitic drugs. This includes people with compromised immune systems and infants born to infected mothers. The complications of toxoplasmosis can be serious and even fatal in these situations.

See your doctor if you have HIV, are pregnant, or are thinking about becoming pregnant and believe you have been exposed to toxoplasmosis. Seek immediate medical care (call 911) for symptoms of severe toxoplasmosis, such as blurred vision, confusion, and loss of coordination, in someone with a weakened immune system.

What are the different types of toxoplasmosis?

Most cases of toxoplasmosis are asymptomatic or very mild. When disease develops, it can take several forms including:

  • Acute toxoplasmosis: This is the initial form of the infection that is usually asymptomatic and self-limited. Up to 20% of people develop swollen lymph nodes. Out of this group, a few will have other mild flu-like symptoms

  • CNS (central nervous system) toxoplasmosis: This form affects the brain and occurs in people with a weakened immune system. For people with HIV, it is an AIDS-defining illness.

  • Congenital toxoplasmosis: This form affects babies born to mothers who become infected during or shortly before pregnancy. It ranges from mild disease, to birth defects that may or may not show up right away, to death before or shortly after birth.

  • Ocular (eye) toxoplasmosis: This form is usually a reactivation of a congenital infection that occurs in the teens or 20s. In rare cases, it is the result of an acquired infection later in life.

  • Disseminated toxoplasmosis: This form affects areas outside the CNS and eyes. It almost always occurs in very severely immunocompromised people. It can cause disease in the lungs and heart and is usually fatal without prompt treatment.

What are the symptoms of toxoplasmosis?

Most people who get toxoplasmosis never develop symptoms or the symptoms they get are mild and nonspecific. Because of this, they never know they have the infection. This does not pose a risk to other people, except in the case of mother-to-child transmission.

Common symptoms of toxoplasmosis

In mild, acute disease, symptoms are flu-like when they occur and include:

Serious symptoms that might indicate a life-threatening condition

In people with weakened immune systems, toxoplasmosis can be severe and even fatal. Seek immediate medical care (call 911) if you, or someone you are with, have any of these serious symptoms including:

  • Blurred or reduced vision

  • Confusion, seizures or coma

  • High fever

  • Poor coordination or one-sided weakness

  • Trouble breathing or speaking

If your immune system is weak due to disease or drugs, always contact your doctor for new or changing symptoms. Flu-like symptoms can be a sign of a variety of problems. Seeing your doctor is the best way to ensure proper diagnosis and treatment.

What causes toxoplasmosis?

Toxoplasmosis is an infection with the parasite Toxoplasma gondii. The parasite is not transmitted from person to person. Instead, people get toxoplasmosis by:

  • Drinking contaminated water
     
  • Eating unwashed fruits and vegetables or undercooked contaminated meat, especially lamb, pork and venison, or shellfish
  • Ingesting the parasite on accident after handling contaminated food or drink, working in contaminated soil, or touching anything that contacted cat feces and not washing your hands
  • Passing the parasite from mother to child during pregnancy
  • Receiving infected blood or organ donation (rare)
  • Using contaminated utensils or containers to eat or drink

Once in the body, the parasite forms cysts in tissues, such as the muscles, nerves, brain, eye and heart. However, the immune system is able to keep the cysts dormant. If the immune system becomes weak, the parasite can activate and spread to other parts of the body.

What are the risk factors for toxoplasmosis?

Anyone can get toxoplasmosis and most people never know it. However, there are factors that increase the risk of developing severe disease including:

  • Being born to a mother with a recent toxoplasmosis infection just before or during pregnancy

  • Having HIV

  • Taking immunosuppressant drugs

  • Undergoing cancer chemotherapy

Reducing your risk of toxoplasmosis

It can be hard to avoid exposure to Toxoplasma gondii and millions of Americans currently have toxoplasmosis. You may be able to lower your risk of toxoplasmosis infection by:

  • Cleaning utensils and food preparation equipment thoroughly

  • Covering sandboxes that cats may use as a litter box

  • Not eating raw or undercooked meat or shellfish or drinking unpasteurized milk

  • Washing fruits and vegetables before consuming them

  • Washing your hands after cleaning a cat’s litter box

  • Wearing gloves while gardening or doing yardwork

If you are pregnant or immunocompromised, there are additional precautions you should take if you are around cats. If possible, have someone else clean your cat’s litter box. Otherwise, wear gloves and a mask, wash your hands thoroughly afterwards, and change litter daily. Avoid stray cats and kittens. And make sure your cat does not eat prey or raw food.

How do doctors diagnose toxoplasmosis?

Most cases of toxoplasmosis resolve on their own and never require a specific diagnosis. When disease is severe or someone is immunocompromised, doctors need to find the microorganism that is causing symptoms. This may involve diagnostic testing including:

  • Blood tests to look for antibodies to the parasite, which is usually how doctors diagnose toxoplasmosis

  • Imaging exams of the brain, including CT (computed tomography) and MRI (magnetic resonance imaging)

  • Lumbar puncture, or spinal tap to see if the cerebrospinal fluid contains evidence of the parasite

  • Biopsy from the brain or other organ or area to test it for the parasite

Toxoplasmosis testing is not a routine part of prenatal care. However, if your doctor suspects exposure, you may need to get blood tests to look for antibodies. Positive results may mean your doctor will order additional testing to see if your baby has the infection too.

Your doctor may also ask you several questions related to your symptoms and exposure including:

  • What symptoms are you experiencing and how severe are they? 

  • How long have you had these symptoms?

  • Are your symptoms continuous or do they come and go?

  • What do you do for a living?

  • Do you garden or work with soil or landscaping? Do you wear gloves?

  • Have you recently eaten raw or undercooked meat or shellfish?

  • Do you own a cat or care for someone else’s? Who cleans the litter box?

  • What medical conditions do you have?

  • What medications do you take?

How is toxoplasmosis treated?

Mild cases of toxoplasmosis usually do not require treatment. They are typically self-limited and resolve on their own over the course of several days or weeks.

If you develop symptoms of acute toxoplasmosis, medications can treat the infection. Drugs doctors use to treat toxoplasmosis include:

  • Pyrimethamine plus leucovorin or folic acid to prevent bone marrow suppression from pyrimethamine

  • Sulfadiazine, clindamycin or atovaquone in addition to pyrimethamine

  • Trimethoprim-sulfamethoxazole (Bactrim) as an alternative to pyrimethamine combination therapy

Treatment usually takes several weeks. Relapses are common in immunocompromised people. Should this happen, chronic maintenance therapy is necessary.

For eye infections, doctors add a corticosteroid.

What are the potential complications of toxoplasmosis?

Most people with healthy immune systems recover from toxoplasmosis without complications. When eye infections reactivate, it can lead to blindness without proper treatment.

Complications of toxoplasmosis are more likely in people with weakened immune systems. The most serious of these is encephalitis. This brain infection can lead to seizures and death without prompt treatment.

Newborns who contract toxoplasmosis from their mothers are at risk of the following complications:

  • Blindness and other vision problems

  • Blood cell disorders, such as anemia and thrombocytopenia

  • Hearing loss

  • Jaundice and other liver and spleen problems

  • Mental disability

Infection early in pregnancy can also lead to premature birth and the problems that accompany it. Prenatal care from the first signs of pregnancy can help ensure both mom and baby remain as healthy as possible.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jun 2
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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  2. Toxoplasmosis. Centers for Disease Control and Prevention. https://www.cdc.gov/parasites/toxoplasmosis/
  3. Toxoplasmosis. Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/diseases-conditions/toxoplasmosis/symptoms-causes/syc-20356249
  4. Toxoplasmosis. Merck Manual Professional Version. https://www.merckmanuals.com/professional/infectious-diseases/extraintestinal-protozoa/toxoplasmosis
  5. Toxoplasmosis. Nemours Foundation. https://kidshealth.org/en/parents/toxoplasmosis.html