Toxoplasmosis is an infectious disease caused by the parasite, Toxoplasma gondii, which is found throughout the world, including in the United States and other developed nations.

Cats (both wild and domestic) are the main hosts of this parasite. Cats excrete millions of these parasites in each stool for up to several weeks after becoming infected. Contact with an infected cat’s feces is the primary method of transmitting the parasite. Many different mammals (e.g., cows, pigs) and birds (including chickens) can become infected with the parasite by ingesting soil or feed contaminated with an infected cat’s feces. One way cats may become infected is by eating infected rodents, birds or other small animals.

Cats are called the definitive host because they are the only hosts that can produce the adult, mature stage of the parasite. Other animals, including humans, are called intermediate hosts.

People may become infected with the Toxoplasma parasite in a variety of ways, including:

• Contact with cat feces
  
  
• Consuming infected meat that is raw or undercooked
  
  
• Consuming unwashed fruits or vegetables grown in contaminated soil
  
  
• Transmission by an infected pregnant woman to her fetus

Infection by the Toxoplasma parasite is common and it does not pose a threat to most healthy people. A healthy, functioning immune system is able to combat the parasite and prevent symptoms of illness. However, toxoplasmosis can be extremely dangerous for certain populations, including infants born to women who become infected during pregnancy, and individuals with compromised immune systems.

In the rare cases where generally healthy people develop symptoms of infection, the symptoms are typically mild, and may resemble the flu or mononucleosis (e.g., muscle aches, fever). People with weakened immune systems may exhibit more severe signs of infection, such as confusion and seizures. Babies born to mothers who were exposed to the Toxoplasma parasites during pregnancy may have symptoms including an enlarged head, liver or spleen, seizures, eye infections, yellowing of the skin and the whites of the eyes (jaundice), and developmental delays.

In people with healthy immune systems, medical treatment for toxoplasmosis is usually not necessary because minor symptoms typically subside within a few weeks. However, when severe symptoms are present, medical treatment is urgent. Left untreated, toxoplasmosis can cause organ damage (e.g., brain, heart, muscles) and may be potentially life-threatening. People with weakened immune systems should consult their physicians about a blood test for Toxoplasma antibodies.

In addition, pregnant women who may have come into contact with the Toxoplasma parasites need to undergo testing to ensure that parasites were not passed to the fetus via the placenta. Toxoplasmosis acquired by the fetus (congenital toxoplasmosis) may result in miscarriage, stillbirth or birth defects.

Antibiotics specifically designed to kill the parasites are available to treat toxoplasmosis, though they can sometimes have adverse side effects (e.g., suppression of bone marrow). The best prevention method is to avoid contact with potentially contaminated sources (e.g., cat feces, raw meat, unpasteurized milk) that may cause infection.

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.

Toxoplasmosis is an infection caused by a single–celled protozoan parasite (Toxoplasma gondii) that is carried in many different mammals (including humans) and birds. But because it reproduces only in cats, wild and domestic cats are the parasite’s definitive host (carrier of the disease). Cats can contract the disease if they eat infected prey, undercooked or raw contaminated meat or come into contact with another cat’s infected feces. Toxoplasmosis can easily spread to almost any other warm-blooded animal (or human) that shares their environment.

The major risk factors for healthy people to contract toxoplasmosis include:

• Access to cats. Contact with cats, their feces and litter boxes. Such access can increase the risk of contracting toxoplasmosis and contaminating food or water. Even people who are not cat owners may be exposed unknowingly if cats enter their yards or children’s sandboxes or other play areas.
  
  
• Poor food and water hygiene. Food items such as fruits or vegetables grown in contaminated soil or contaminated meat may harbor the parasite. It can be spread through kitchen utensils, and surfaces. Raw eggs and unpasteurized dairy products may also harbor the parasite.
  
  
• Infected organ transplant or blood transfusion. In extremely rare cases, toxoplasmosis can be transmitted through an organ transplant or blood transfusion from an infected donor.

Infants can contract toxoplasmosis while still in the womb of an infected mother. Transmission of the active infection is more common later in pregnancy, but more serious early in pregnancy. It is unknown whether breast milk can transfer an active infection from mother to infant. No research has documented the occurrence of this type of transmission, although it may be possible. According to the U.S. Centers for Disease Control and Prevention, the likelihood of transmitting toxoplasmosis in this manner is very small.

People with impaired immune systems also are at greater risk for contracting toxoplasmosis. These include:

• Chronic illness (e.g., HIV, AIDS, cancer). People with diseases that weaken their immune systems are more susceptible to developing severe to deadly symptoms as a result of toxoplasmosis.
  
  
• Chemotherapy. This type of cancer treatment can lower the defenses of the immune system, making it difficult for the body to fight even minor infections.
  
  
• Certain medications. Use of certain medications (e.g., steroids, immunosuppressant drugs) for the treatment of various medical conditions, including organ transplants, suppress the immune system and may make a person more susceptible to developing severe or even fatal complications due to 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

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 there 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.
  
  
  Biopsy. 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:

• Amniocentesis. 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.
  
  
• Ultrasound. 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.

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.

Prevention of toxoplasmosis is the best approach to avoiding toxoplasmosis, especially for those at an increased risk of developing severe to life-threatening complications of infection. Antibiotic drugs used to treat toxoplasmosis may have adverse side effects (e.g., bone marrow suppression, liver toxicity, diarrhea). In addition, treatment during pregnancy may prove harmful to the fetus.

The most effective prevention measures involve managing contact with cats.  People do not have to give up their cat or a job that places them in contact with cats. Cats only pass the Toxoplasma parasites in their stool for up to several weeks after initial exposure to the parasite. Thereafter, cats do not shed the parasites in their stool. Still, for pregnant women or people with weakened immune systems who own cats or come in contact with them (e.g., by working at a veterinary clinic or animal shelter), there are special precautions to follow to reduce the risk of contracting toxoplasmosis. These preventive methods include:

• Have a healthy, nonpregnant household member clean the litter box. If this cannot be done, gloves and a mask that covers the nose and mouth (to prevent inhalation of contaminated dust particles) should be worn while changing the litter, followed by a thorough washing of the hands with soap and hot water. Litter boxes should be changed daily. The parasites released in cat feces require at least 24 hours before they become infectious. Litter boxes should also be washed for five minutes with nearly boiling water and soap. In addition, the litter box or cat should never be allowed on the kitchen counter or any surface where food is prepared.
  
  
• Keep pet cats healthy. Cats should be kept indoors and fed only dry or canned cat food, never raw or undercooked meat. Cats become infected from eating infected prey (e.g., birds, rodents) or undercooked meat that contains the parasite causing toxoplasmosis.
  
  
• Refrain from adopting stray cats, especially kittens. Most cats do not show signs of toxoplasmosis infection, and although they can be tested for the disease, test results may take up to a month. During that time, individuals can contract the disease. Younger cats are more likely to be exposed to the parasite for the first time, which is when they shed the parasite in their feces. Older cats may have already been exposed and are no longer shedding the parasite in their feces.

In addition, people can take other measures to reduce the risk of contracting toxoplasmosis. These include:

• Do not eat raw or undercooked meat (e.g., beef, lamb, pork, venison) or chicken. Meat can harbor Toxoplasma parasites. All red meat should be cooked to a temperature of at least 160 degrees Fahrenheit (71 degrees Celsius), and until no trace of pinkness remains and juices run clear. Poultry should be cooked to a minimum internal temperature of 165 degrees Fahrenheit (73.9 degrees Celsius), according to the Food Safety and Inspection Service. Another precaution is refraining from tasting meat before it is fully cooked. Red meat that has been smoked or cured may be safe to consume, according to the Centers for Disease Control and Prevention (CDC).
  
  
• Thoroughly wash kitchen utensils and surfaces. After food preparation that involves raw meat or chicken, thoroughly wash all cutting boards and surfaces, knives or other utensils in hot water with soap to prevent contamination of other foods. In addition, washing hands carefully after handling raw meat is recommended.
  
  
• Wash all fruits and vegetables. If possible, use a vegetable soap to wash fruit and vegetables, especially if eating them raw. Otherwise, scrub them carefully to reduce the risk of infection.
  
  
• Reduce insect exposure to food. Because flies, cockroaches and other insects may transfer parasites from infected fecal matter to food, it is important to prevent insects from being able to access food or food preparation sites. This may include keeping food items covered when eating outdoors, or installing screens on doors or windows that may be kept open.
  
  
• Avoid unpasteurized dairy products, raw eggs and unfiltered water. All of these may contain Toxoplasma parasites. It is best not to eat foods with raw eggs such as cookie dough or eggnog. Eggs should be cooked until the yolk is hard.
  
  
• Wear gloves when gardening or handling soil. Although gardening activities are relaxing, they can expose a person to toxoplasmosis from parasites in the soil. Gloves should be worn whenever working outdoors, and afterwards, hands should be thoroughly washed with soap and water, especially before preparing or eating food.
  
  
• Avoid children’s sandboxes. Cats may use them as litter boxes and the parasite may be present in the sand. Sandboxes should be covered when not in use.

Preparing questions in advance can help patients have more meaningful discussions with healthcare professionals regarding their conditions. Patients may wish to ask their doctor the following questions related to toxoplasmosis:

1. What symptoms indicate that I may have toxoplasmosis?
   
   
2. How could I have been exposed to the Toxoplasma parasite? Is it possible to get infected if I don’t have cats?
   
   
3. What tests will you need to perform to determine whether I have toxoplasmosis?
   
   
4. If I have toxoplasmosis, am I contagious? Are others in my household at risk of developing an infection?
   
   
5. What types of medications do you recommend for me? What side effects are possible? Will these medications interfere with any of my current medications or supplements?
   
   
6. How long will I have to take this medication?
   
   
7. How will you know I don’t have the infection anymore?
   
   
8. Once I have had toxoplasmosis, can I become infected again?
   
   
9. What are my chances of developing toxoplasmosis during pregnancy? If I become infected during pregnancy, what can be done to protect my baby from complications? How will I know if my baby is at risk for problems later in life?
   
   
10. How can toxoplasmosis be prevented?