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:

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: 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: 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:

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. For pregnant women with an active toxoplasmosis infection, a physician may order the following additional tests to determine whether the baby is also infected: 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:

Medications

• 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.

Alternatives

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.

Last updated 4 July 2015