What Is Toxoplasmosis?

A Parasitic Infection

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Toxoplasmosis is a disease caused by the parasite Toxoplasma gondii. This parasite is a tiny single-celled organism called a protozoan. People can acquire it from undercooked meat and exposure to cat feces

In healthy individuals, this infection doesn’t usually do lasting damage and often shows no symptoms. But, pregnant people, their fetuses, and people with a weakened immune system are at risk of more dangerous infections.

Toxoplasma grows in and affects various parts of the body, including the brain, eyes, and muscles of the heart and body. It forms bubbles in the tissue called cysts that house the parasite. These cysts may persist after the person is no longer sick.

More than 40 million people in the United States have toxoplasmosis, but they don’t all get sick. It’s most dangerous to people with a weakened immune system.

This article will cover the symptoms, causes, diagnosis, and treatment of toxoplasmosis. 

Close-up of cutting an undercooked piece of venison steak

kajakiki / Getty Images

Types of Toxoplasmosis

Toxoplasmosis may be mild or severe. Those at risk of severe disease are those with weakened immune systems. This includes people taking certain medications and those with autoimmune disorders, cancer, or certain immune system infections, like human immunodeficiency virus (HIV). 

There are three primary forms of toxoplasmosis that depend on when and how it was contracted, as follows:

  • Acute toxoplasmosis: If a relatively healthy person acquires toxoplasma infection, they can have flu-like symptoms. Acute toxoplasmosis is the most common form of infection. The person may have a fever, swollen lymph nodes, and muscle aches but no long-term health problems.
  • Congenital toxoplasmosis: If a pregnant person acquires a toxoplasma infection, they may pass it to the fetus. Congenital toxoplasmosis can lead to serious health problems for the baby. These include congenital (present at birth) disabilities and developmental delays.
  • Chronic toxoplasmosis: If a person with a weakened immune system acquires a toxoplasma infection, they may get chronic toxoplasmosis. This form can cause serious health problems, including brain and eye damage.

Toxoplasmosis Symptoms

The most common symptoms of toxoplasmosis in healthy individuals include fever, swollen lymph nodes, and muscle aches and pains. Many people with toxoplasmosis don’t have any symptoms.

People with weakened immune systems, such as those with HIV, have more severe symptoms. This can include brain and eye damage.

People with toxoplasmosis may have the following:

  • Flu-like symptoms (fever, swollen lymph nodes, and muscle aches and pains)
  • Headaches
  • Fatigue
  • Confusion
  • Eye problems (blurred vision or sensitivity to light)

Even in healthy people, these symptoms may last weeks or months. After symptoms improve, the person has dormant toxoplasma parasites in their body in cysts. Because these cysts hide the parasite in the body, toxoplasmosis never really goes away.

If a previously healthy person with inactive toxoplasmosis infection develops a weakened immune system, the parasite can reactivate and cause disease.

In pregnant people, active toxoplasmosis infection can cause pregnancy loss or congenital disease of the fetus.

Congenital toxoplasmosis typically results in a larger or smaller head than is typical. It can also cause symptoms, including:

  • Enlarged liver and spleen
  • Jaundice (yellowing of skin and eyes)
  • Anemia (a low number of healthy red blood cells)
  • Seizures
  • Eye conditions such as scarring, inflammation, retinal detachment, vision impairment
  • Brain conditions such as hydrocephalus (a buildup of cerebrospinal fluid in the hollow spaces of the brain)
  • Intellectual disabilities
  • Hearing loss

Symptoms of congenital toxoplasmosis may not appear until months or even years after birth. Newborns may appear healthy but have symptoms later in life.


Toxoplasmosis is caused by the parasite Toxoplasma gondii. In the wild, toxoplasma is transmitted between rodents and cats and birds. Housecats can acquire it if they venture outside. Farm or game animals can acquire toxoplasma in their environment.

Humans can acquire toxoplasmosis from exposure to the parasites’ eggs in their environment. The parasite eggs can be in the soil of, for instance, a home garden. Make sure to clean all garden produce well before eating, and always wash your hands after working in the soil. 

Humans may acquire toxoplasmosis by any of several routes: 

  • Eating undercooked meat of animals infected with toxoplasma from their environment
  • Eating food or drinking water contaminated with toxoplasma from cat feces, for example, from a home garden
  • Coming into contact with contaminated soil or changing a cat's litter box if the animal has acquired a toxoplasma infection while out of the house
  • Exposure to infected blood or organs through transfusion or transplantation
  • Exposure to the fetus through the placenta when the pregnant person has toxoplasmosis 

If you have a cat that goes outside, you can acquire toxoplasmosis. While outside, the cat may come into contact with toxoplasma and acquire an infection. Once infected, the cat has parasite eggs in their feces. Cleaning the cat’s litter box, especially if you have a weakened immune system, can lead to toxoplasmosis. 

Toxoplasmosis is not considered a sexually transmitted infection (STI). Toxoplasma can be transmitted through sexual contact, but that is atypical. However, it is more likely to cause long-term, chronic infections in people with the STI HIV who have weakened immune systems.


If a healthcare provider suspects a toxoplasma infection, they typically order tests to look for antibodies to the parasite in the blood.

To determine when someone acquired the infection, which can be important for pregnant people, the test can compare the levels of two types of antibodies: immunoglobulin M (IgM) and immunoglobulin G (IgG):

  • High IgM antibodies that recognize toxoplasma indicate a recent infection.
  • High IgG antibodies that recognize toxoplasma indicate that a person has acquired the infection at some time in the past. It does not necessarily mean that they have an active infection. 

In some cases, a healthcare provider may also recommend imaging tests, such as magnetic resonance imaging (MRI) or computed tomography (CT) scan, to determine if toxoplasmosis has caused any damage to the brain or other organs. They may look into the eyes for lesions.

The healthcare provider may want to examine specific tissues or bodily fluids under a microscope to see if they can see the parasite or cysts directly. For this, they may want to perform a biopsy (removing a small sample of tissue for examination in a lab) or collect cerebrospinal fluid from the spine.

To test if a fetus has been exposed to the parasite, tests can detect the parasite’s genetic material in the amniotic fluid collected by amniocentesis.


Treatment for toxoplasmosis depends on the person’s immune health and if they are pregnant, as follows:

  • Most healthy people who are not pregnant but have mild toxoplasmosis symptoms can weather their illness at home without special treatment. 
  • Previously healthy people with active toxoplasmosis making them ill can be treated with medications. 
  • Treatment can’t eliminate the parasite in healthy pregnant people, newborns, or infants, but medication may reduce the number of parasites and help get them to an inactive phase. 
  • People with compromised immune systems who develop toxoplasmosis are treated with medications. They will likely need to stay on them for the rest of their lives, as the parasite can reactivate. 

A qualified healthcare provider needs to choose testing and treatment as doses and duration may vary. Medications used to treat toxoplasmosis include sulfadiazine, Daraprim (pyrimethamine), and folinic acid (leuvocorin). In some cases, clindamycin or azithromycin may be used as well.


Most healthy people have no symptoms of toxoplasmosis. People who do have symptoms often recover with no long-term effects. But because these cysts stay in the body, toxoplasmosis never goes away and can reactivate if a person’s immune system weakens.

Children born with congenital toxoplasmosis have symptoms their entire lives. Complications of toxoplasmosis may include:

  • An abnormal buildup of fluid deep within the brain called hydrocephalus
  • Blindness or severe visual disability
  • Severe intellectual disability or other brain problems

People with weakened immune systems who acquire a toxoplasmosis infection need to be on medications for the rest of their lives to keep the parasites at bay. 


Coping with toxoplasmosis can be challenging, especially for individuals with weakened immune systems or pregnant people. Here are a few strategies that may help:

  • Follow your treatment plan: If you have been diagnosed with toxoplasmosis, it is vital to follow your treatment plan as directed by your healthcare provider. This may include medication to help clear the infection and prevent serious complications.
  • Take care of your overall health: Individuals with weakened immune systems are at a higher risk of severe complications from a toxoplasma infection. Taking care of your overall health by getting enough sleep, eating a balanced diet, and exercising regularly can help to boost your immune system.
  • Seek emotional support: Toxoplasmosis can be a stressful and isolating experience, especially if you’re worried about transmitting it to the fetus. Talk to a healthcare provider and seek emotional support from friends, family, or a therapist.

Pregnant people with toxoplasmosis should consult with a healthcare provider and follow the recommended guidelines to protect the fetus's health.


Toxoplasmosis is a disease caused by the parasite Toxoplasma gondii. This parasite infects the brain, eyes, and muscles. It forms bubbles in the tissue called cysts that house the parasite. These cysts may persist after the person is no longer sick.

The three forms of toxoplasmosis are: 

  • A healthy person may have flu-like symptoms called acute toxoplasmosis. 
  • A pregnant person may pass it to the fetus, called congenital toxoplasmosis, and can lead to serious health problems for the baby. 
  • A person with a weakened immune system may get chronic toxoplasmosis, which can cause serious health problems.

The most common way humans acquire toxoplasmosis is by eating undercooked meat with cysts. It can also be in their environment, such as on unwashed vegetables from the garden or in cat feces from a litter box. 

Treatment for toxoplasmosis isn’t needed in most healthy people. Others may get a combination of medicines.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Jennifer Welsh
Jennifer Welsh is a Connecticut-based science writer and editor with over ten years of experience under her belt. She’s previously worked and written for WIRED Science, The Scientist, Discover Magazine, LiveScience, and Business Insider.