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Toxoplasma Gondii Infection, Toxoplasma Infection

What is Toxoplasmosis?

Toxoplasmosis is an infectious disease caused by the parasite Toxoplasma gondii. This parasite is carried by many different mammals including rodents, cats, pigs, cows, sheep, goats and humans, as well as birds (including chickens). Cats are the only hosts (carriers of the disease) in which the parasite reaches its sexual maturity, releasing eggs in cat feces that become infectious parasites. Thus, wild and domestic cats are called the parasite's definitive hosts. Contact with an infected cat's feces is the primary method of transmitting the parasite.

Cats may become infected with the Toxoplasma parasite by eating infected rodents, birds or other small animals. They may also become infected through contact with the feces of another infected cat. Once ingested, the parasites invade the lining of the cat's intestine and produce oocysts (eggs containing the fertilized cell of a parasite) that are then released with the cat's stool.

An infected cat may release oocysts in its feces for up to a few weeks after initial exposure to the parasite. Millions of oocysts may be present in each stool a cat releases during this time. After being expelled from the cat's body, the oocysts require one to five days to become mature and infectious parasites. These infectious parasites can then survive in certain environments and remain infectious for up to a year. They are resistant to disinfectants, freezing and drying, although they may be killed with heat – at temperatures of at least 160 degrees Fahrenheit (71 degrees Celsius).

After an initial infection, cats typically develop immunity against future Toxoplasma infections and do not pass these parasites in their stool again after their primary infection. Cats infected with toxoplasmosis often appear healthy, even while they are passing the parasites in their stool.

The feces of an infected cat can contaminate soil, water and litter boxes. The parasite may be transmitted to other animals (e.g., cows, pigs, chickens) when they ingest soil or feed that has been contaminated by an infected cat's feces. When meat from these animals is not properly cooked and is consumed by humans (e.g., when people eat undercooked or raw meat), the parasite can be transmitted to humans. Cats may also become infected by consuming raw or uncooked contaminated meat products. Rodents, birds and other small animals may carry the parasite after coming into contact with the oocysts in cat feces. Flies, cockroaches and other insects may transfer the parasite from contaminated fecal matter to food.

Handling contaminated feces or consuming anything that has come into contact with it (e.g., water, unwashed fruits or vegetables grown in contaminated soil) can also transmit the parasite to humans. Often this involves touching the contaminated item (e.g., cat feces while cleaning a litter box, soil while gardening), and then touching one's own mouth, effectively introducing the parasite to the body. Transmission may also occur when eating contaminated foods or drinking contaminated water. It may also occur by inhaling dust that contains the parasite.

People can also become infected with toxoplasmosis through blood transfusions or organ transplants taken from infected donors. However, this is very rare in the United States due to stringent screening procedures for blood donors.

When parasites enter the human body (usually through the mouth), they can penetrate the lining of the digestive tract and can travel to organs including the brain, skeletal muscles, heart, eyes, lungs and lymph nodes. However, Toxoplasma parasites usually cause no symptoms in healthy people. If symptoms do occur, they are usually mild and may resemble the flu. In most cases, symptoms of infection resolve without treatment. The initial infection does not occur again, although the Toxoplasma parasite can remain dormant in the body for the rest of a person's life. More than 60 million Americans carry the Toxoplasma parasite, according to the U.S. Centers for Disease Control and Prevention (CDC). These parasites may become reactivated anytime a person experiences problems with immune system functioning.

The only method of human-to-human transmission of toxoplasmosis occurs in women who become infected with the Toxoplasma parasite for the first time while they are pregnant. In these cases, they can pass the parasite on to their developing fetus, with severe to deadly consequences. Congenital toxoplasmosis may cause miscarriage, stillbirth, birth defects or problems that affect the child later, such as blindness, hearing loss and learning disabilities. Most newborns with toxoplasmosis have no symptoms at birth but can develop difficulties later in life. Pregnant women with active infection of toxoplasmosis have up to a 50 percent chance of passing the disease to their unborn child (congenital toxoplasmosis), according to the National Institutes of Health (NIH). If a pregnant woman has been previously infected (at least six to nine months prior to becoming pregnant), there is very little risk of harm to the fetus.

In patients with immune system deficiencies, such as those related to cancer treatment or HIV/AIDS, symptoms of an initial toxoplasmosis infection can be severe. In these people, toxoplasmosis can spread out of control and damage the brain, lungs, heart, eyes or liver. Infection can lead to severe seizures, life-threatening illness such as encephalitis (severe brain infection), and other neurological problems.

Symptoms of Toxoplasmosis

Most people infected with toxoplasmosis never develop signs and symptoms because their bodies fight off the parasites causing the disease. In the few cases where healthy people become infected, symptoms are often mild and go away without treatment. The incubation period may range from several days to several weeks after infection before symptoms appear.

Symptoms of toxoplasmosis in healthy people may last several weeks or more and may include:

  • Flu-like symptoms (e.g., fever, muscle aches)
  • Enlarged lymph nodes in the head and neck
  • Fatigue
  • Headache
  • Sore throat
In rare cases, healthy people who develop symptoms as a result of toxoplasmosis may experience eye disease.

People with weakened immune systems are more likely to develop severe symptoms of toxoplasmosis, including:
  • Symptoms of brain lesions (e.g., fever, headaches, confusion, seizures)
  • Nausea/vomiting
  • Poor coordination
  • Symptoms of lung infection (e.g., shortness of breath, dry cough, coughing up blood)
  • Partial loss of vision or blurred vision (due to severe inflammation of the retina)
If left untreated, toxoplasmosis in people with weakened immune systems may lead to serious conditions that can become life-threatening, such as respiratory failure (due to lung infection) and a severe infection of the brain (encephalitis).

Most infants infected with toxoplasmosis while in the womb (congenital toxoplasmosis) exhibit no signs of infection at birth, although they often develop problems later in life. When signs of toxoplasmosis occur in newborns and infants, they may include:
  • Unusually small body size
  • Lazy or misaligned eye (strabismus), among other eye problems
  • Enlarged head (macrocephaly) or an unusually small head (microcephaly)
  • Convulsions or seizures
  • Yellowing of the skin and the whites of the eyes (jaundice)
  • Enlarged lymph nodes
  • Abnormal bruising and/or rashes
  • Developmental delays
In addition, signs of congenital toxoplasmosis may differ, depending when during the pregnancy the parasites were transmitted to the fetus. Infections occurring during the first trimester of pregnancy often end in miscarriage or stillbirth.

How is it diagnosed?

Unless screening tests are performed, toxoplasmosis may be difficult to diagnose because early signs and symptoms (when they occur) resemble those of more common illnesses such as the flu and mononucleosis.

First, a physician will review the patient's medical history and perform a physical examination. A medical history will help the physician determine if The HIV virus, which causes acquired immune deficiency syndrome (AIDS), attacks the body's immune sythere is an underlying medical condition that may weaken the body's immune defenses against toxoplasmosis, such as HIV or AIDS, cancer or an inherited immune deficiency. In addition, a physician will review any medications being taken by the patient to check for any drugs that may suppress or damage the body's immune defenses.

The physician will also ask about the patient's exposure to cats, especially outdoor cats that kill and eat small prey that may be infected with the parasites that cause toxoplasmosis. To evaluate the risk of food–related toxoplasmosis (e.g., contaminated raw meats or unwashed vegetables), the physician will ask if the patient has recently ingested these types of foods. In addition, the physician will assess whether the patient has an occupation that places him or her at high risk of exposure to Toxoplasma parasites, such as working with food or animals.

If toxoplasmosis is suspected, the following screening tests may be ordered:

Blood tests

Laboratory analyses to check for antibodies (defensive proteins made by the immune system) against the Toxoplasma gondii parasite, which causes toxoplasmosis. Because these antibody tests can be difficult to interpret, the U.S. Centers for Disease Control and Prevention (CDC) recommends that all positive test results be confirmed by a laboratory that specializes in diagnosing toxoplasmosis.
Depending on the blood levels of certain antibodies, a physician may be able to tell whether a patient has an active toxoplasmosis infection or whether primary infection occurred in the past.

MRI (magnetic resonance imaging)

A safe and noninvasive or minimally invasive imaging test that uses a magnetic field and radio waves to create cross–sectional images of organs in the body. This type of testing may be done on patients with severe symptoms (e.g., seizures, coughing up blood) where organ damage (e.g., brain, heart) is suspected due to toxoplasmosis.


In rare cases, especially if a patient does not respond to treatment, a small sample of tissue from the affected organ, such as the brain, may be taken for laboratory analysis to check for the presence of Toxoplasma parasites. This is done only in cases where a toxoplasmosis patient has developed life–threatening complications from the infection.
For pregnant women with an active toxoplasmosis infection, a physician may order the following additional tests to determine whether the baby is also infected:


A procedure where a physician uses a fine needle to remove a small amount of fluid from the fluid–filled amniotic sac that lines a woman's uterus. Tests are then performed on the amniotic fluid to check for evidence of toxoplasmosis. This is the primary test performed to determine if a fetus has become infected, and is done around 18 weeks of pregnancy or later. However, with this type of testing there is a slight risk of miscarriage or injury to the fetus. In addition, a pregnant woman may experience minor discomfort, such as cramping, leaking fluid or irritation where the needle was inserted.


An imaging test that uses sound waves to produce images of the fetus in the uterus. This type of test can show whether the fetus has certain physical signs (e.g., enlarged head) associated with toxoplasmosis. However, it is not used for a definitive diagnosis of the disease.
Because most infants with toxoplasmosis do not display signs at birth, babies born to mothers infected with toxoplasmosis during their pregnancy will need to undergo thorough physical examinations after birth and follow–up blood tests during their first year of life.

How is Toxoplasmosis treated?

Most healthy people do not require medical treatment for toxoplasmosis because their symptoms, if any, are usually mild and their immune system defends the body from developing symptoms as a result of infection. But if a patient has severe symptoms of toxoplasmosis or has a compromised immune system due to chronic illness or the use of certain medications (e.g., steroids), immediate medical treatment is crucial to prevent subsequent organ damage. Healthy people who develop eye disease as a result of toxoplasmosis may also require treatment.

Toxoplasmosis is primarily treated with certain types of antibiotics (e.g., pyrimethamine, sulfadiazine, clindamycin, spiramycin) to kill the parasites responsible for toxoplasmosis. In addition to treating the disease, antibiotics may also help prevent recurrence in individuals with weakened immune systems. These antibiotics may also reduce the body's ability to absorb folate, a vitamin necessary for blood cell production and important for proper fetal development during pregnancy. This is especially true when these antibiotics are taken in high doses for long periods of time. Patients undergoing treatment for toxoplasmosis will need to have blood tests twice a week to monitor their platelet and blood cell levels.

Special treatment considerations may apply to the following populations affected by toxoplasmosis:

  • People with weakened immune systems. Potential side effects of most medications, including those used to treat toxoplasmosis, may be more severe in people with immune system dysfunction. Additionally, these patients may need to continue treatment with antibiotics for life. Patients with weakened immune systems, including those with AIDS, may also receive folinic acid (a natural form of folate), which helps prevent the suppression of bone marrow and anemia caused by certain antibiotics.
  • Pregnant women. In addition to antibiotics, women who contract a primary Toxoplasma infection during pregnancy may also be given folate supplements. A lack of folate during pregnancy can result in birth defects.
  • Fetuses. Antibiotic treatment of pregnant women with toxoplasmosis may also stop infection of the fetus, although it will not reverse any damage that may have already occurred. For this reason, if the condition is diagnosed early enough, some parents may choose to medically terminate the pregnancy after a thorough medical diagnosis has confirmed irreversible damage to the fetus.


  • Pyrimethamine, sulfadiazine or trisulfapyrimidines for 3 to 4 weeks and folinic acid to reduce the side effects of pyrimethamine are often prescribed.
  • corticosteroids, if necessary, for inflammation.

What might complicate it?

Complications may include glaucoma, blindness, interstitial pneumonia (inflammation of the tissues surrounding the air passages), myocarditis (inflammation of the heart), partial paralysis, cranial nerve disturbances, and seizures.


Conditions with similar symptoms include CMV, infectious mononucleosis, sarcoidosis, tuberculosis, tularemia, lymphoma, metastatic cancer, herpes simplex, multifocal leukoencephalopathy, fungal encephalitis, vascular stroke, and CNS lymphoma.

Appropriate specialists

Infectious disease specialist, internist and parasitologist.

Notify your physician if

  • You or your child has symptoms of toxoplasmosis.
  • Symptoms worsen or don't improve after diagnosis and treatment.

Last updated 4 July 2015