Toxoplasmosis

What Is Toxoplasmosis?

How Common Is Toxoplasmosis?

Is Toxoplasmosis Contagious?

What Happens to People with Toxoplasmosis?

How Do Doctors Diagnose Toxoplasmosis?

What is the Treatment for Toxoplasmosis?

Can Toxoplasmosis Be Prevented?

Resources

Toxoplasmosis (tox-o-plaz-MO-sis), often called toxo, is a parasitic infection that usually causes no symptoms in healthy people, but it can be serious in people with weak immune systems and in unborn babies.

KEYWORDS

for searching the Internet and other reference sources

Parasitic diseases

Toxoplasma gondii

Zoonoses

What Is Toxoplasmosis?

The parasite Toxoplasma gondii, the organism behind toxoplasmosis, is found in soil and can infect humans and many species of animals. It is often found in cats, and is passed in cat feces (FEE-seez, or bowel movements). Touching dirty litter from a cat’s litter box is one common way that people contract the parasite. Eating undercooked meat or accidentally eating contaminated soil are other ways that people become infected.

Many people who have toxoplasmosis have no symptoms or symptoms that are very mild. However, women who become infected when they are pregnant can pass the organism to the fetus*. In an unborn child, the parasite can cause congenital* toxoplasmosis, a condition that can range from mild to severe and may involve developmental problems and mental retardation, seizures*, and vision problems. Toxoplasmosis also can take a heavy toll on people with weakened immune systems, such as those with AIDS* or cancer, or those who have had an organ or bone marrow* transplant. Toxoplasmosis may affect the brain in these people.

*fetus

(FEE-tus) is the term for an unborn human after it is an embryo, from 9 weeks after fertilization until childbirth.

*congenital

(kon-JEH-nih-tul) means present at birth.

*seizures

(SEE-zhurs) are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.

*AIDS ,

or acquired immunodeficiency (ih-myoo-no-dih-FIH-shen-see) syndrome, is an infection that severely weakens the immune system; it is caused by the human immunodeficiency virus (HIV).

*bone marrow

is the soft tissue inside bones where blood cells are made.

How Common Is Toxoplasmosis?

The U.S. Centers for Disease Control and Prevention estimates that as many as 60 million people in the United States have been infected with T. gondii, but cases of actual disease are much less common. Most people who carry the parasite have no symptoms of illness.

Is Toxoplasmosis Contagious?

Pregnant women who are infected during pregnancy can pass the organism to the unborn child, but this is the only way that it spreads from person to person. Many people contract toxoplasmosis from eating raw or undercooked meat containing the parasite’s cysts*, especially pork and lamb. Others unknowingly ingest the parasite’s eggs after touching cat feces, soil, or anything that has come into contact with cat feces. The eggs can stick to a person’s hands and may eventually end up in the mouth, where they can be swallowed.

*cysts

(SISTS) are shell-like enclosures that contain a small organism in a resting stage.

What Happens to People with Toxoplasmosis?

Most people with the infection have no symptoms. When symptoms do occur, they may include swollen lymph nodes*, muscle aches, headache, and sore throat. For people with weakened immune systems (especially those with AIDS), toxoplasmosis can cause severe infection of the brain or, less commonly, the lungs or heart. As a result, symptoms are worse, and they may include fever, headache, confusion, seizures, blurred vision from inflammation of the retina*, psychosis (sye-KO-sis, form of mental illness in which an individual becomes disconnected from reality), and problems with speech or movement. Severe disease can be fatal.

*lymph

(LIMF) nodes are small, bean-shaped masses of tissue that contain immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.

*retina

(REH-tih-nuhz) is the tissue that forms the inner surface of the back of the eyeballs; it receives the light that enters the eye and transmits it through the optic nerves to the brain to produce visual images.

In some cases, infection in a pregnant woman induces a miscarriage*. Congenital infection in newborns may be marked by small body and head size, jaundice*, rash, fever, anemia*, inflamed retinas, and an enlarged spleen and liver. These children may develop blindness, mental retardation, learning disabilities, and other problems with the central nervous system (the part of the nervous system that includes the brain and spinal cord), such as seizures and difficulty controlling movements. Sometimes the developmental disabilities are present from birth and sometimes they do not appear for many months or years.

*miscarriage

is the ending of a pregnancy through the death of the embryo or fetus before birth.

*jaundice

(JON-dis) is a yellowing of the skin, and sometimes the whites of the eyes, caused by a buildup in the body of bilirubin, a chemical produced in and released by the liver. An increase in bilirubin may indicate disease of the liver or certain blood disorders.

*anemia

(uh-NEE-me-uh) is a blood condition in which there is a decreased amount of oxygen-carrying hemoglobin in the blood and, usually, fewer than normal numbers of red blood cells.

How Do Doctors Diagnose Toxoplasmosis?

If a doctor suspects toxoplasmosis, he or she will draw a blood sample and test it for evidence of the parasite. An eye doctor may use a special lamp called a slit lamp to check the eyes for abnormalities of the retinas. People with weakened immune systems who are more likely to develop a severe infection might have magnetic resonance imaging* (MRI), a computerized tomography* (CT) scan of the head, or rarely, a brain biopsy (removing a small sample of brain tissue to examine) to look for signs of damage caused by the parasite. Infants with congenital toxoplasmosis also will need a CT scan of the head and thorough examination of other areas of the body possibly affected by the parasite.

*magnetic resonance imaging

(MRI) uses magnetic waves, instead of X rays, to scan the body and produce detailed pictures of the body’s structures.

*computerized tomography

(kom-PYOO-ter-ized toe-MAH-gruh-fee) or CT, also called computerized axial tomography (CAT), is a technique in which a machine takes many X rays of the body to create a three-dimensional picture.

What is the Treatment for Toxoplasmosis?

People who have toxoplasmosis but are otherwise healthy do not need any treatment. However, people with weak immune systems, pregnant women, and newborns with the congenital infection are treated with medication. Patients with AIDS often continue taking the medicine even after the infection clears up to keep it from returning.

Healthy people usually have symptoms for only a few days, if at all. In newborns and patients with unhealthy immune systems, the illness can last for weeks or months and cause permanent disability.

Can Toxoplasmosis Be Prevented?

Pregnant women and people whose immune systems are weak can take steps to avoid infection with T. gondii. First, they can be tested for the parasite. If they test positive, they will likely be started on medication for the infection, even if they do not have any symptoms. If they test negative, they can follow some simple measures to keep from becoming infected in the future, such as:

• wearing gloves when gardening and handling soil to prevent infection from parasites in the dirt
• wearing gloves when cooking or having someone who is healthy and not pregnant handle raw meat
• cooking all meat thoroughly, until the juices run clear and it is no longer pink inside
• washing all utensils and cutting boards that have come into contact with raw meat in hot water and soap
• washing hands frequently, particularly after outdoor activities, after preparing food, and before eating

Diseases Associated With Cats

• Cat-scratch disease: an infectious illness that can cause swollen lymph nodes and symptoms similar to those of the flu. It is caused by bacteria carried in cat saliva that usually enter the body from a cat scratch or a bite that breaks the skin.
• Cryptosporidiosis (krip-toh-spor-id-e-O-sis): an intestinal infection caused by a parasite that can live in people and animals, including cats. People pick up the parasite through contact with infected feces and typically have diarrhea and stomach pain.
• Giardiasis (jee-ar-DYE-uh-sis): an intestinal infection caused by a parasite that can live in people and animals, including cats. People become infected when they come into contact with feces from an infected person or animal and typically have diarrhea and an upset stomach.
• Lyme (LIME) disease: a bacterial infection spread to humans by the bite of infected ticks, which can be carried by cats. The illness starts with a distinctive rash and/or symptoms like those of the flu and can progress to a more serious disease with complications affecting other body organs.
• Rabies (RAY-beez): a viral infection of the central nervous system that usually is transmitted to humans by the bite of an infected animal.
• Ringworm: a fungal infection of the skin, scalp, or nails that usually causes red, dry, flaky skin. The fungus also can infect pets such as cats, which can spread the fungus to people.
• Toxocariasis (tox-o-kah-RYE-uh-sis): an infestation in people of a type of parasitic roundworm found in cats (another species is found in dogs). As the worms move through the body, they can affect the eyes and other body organs.
• Toxoplasmosis: a parasitic infection often found in cats, and is passed to humans through contact with cat feces.

• keeping family cats inside and feeding them only dry or canned cat food, because cats can pick up the parasite from eating raw meat
• having someone who is healthy and not pregnant change the cat’s litter box every day
• not touching strange or stray cats or letting any cat into the home that might have lived outside or eaten raw meat

Resources

Organization

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. The CDC is the U.S. government authority for information about infectious and other diseases. It provides information about toxoplasmosis at its website.

Telephone 800-311-3435 http://www.cdc.gov

Website

KidsHealth.org. KidsHealth is a website created by the medical experts of the Nemours Foundation and is devoted to issues of children’s health. It contains articles on a variety of health topics, including toxoplasmosis.

http://www.KidsHealth.org

Toxoplasmosis

Definition

Toxoplasmosis is an infectious disease caused by the one-celled parasitic organism Toxoplasma gondii. Although most individuals do not experience any symptoms, the disease can be very serious and even fatal in fetuses, newborns, and individuals with weakened immune systems.

Description

Toxoplasmosis is caused by a one-celled parasite Toxoplasma gondii. This parasite is found worldwide. It causes infections that can be either acute or chronic. In about 60 percent of healthy adults who become infected, the organism causes no symptoms (asymptomatic). Most of the remaining 40 percent experience mild, flu-like symptoms, low-grade fever , and fatigue that resolve without intervention in a few weeks. Once exposed, reinfection does not occur in healthy individuals. However, in immunocompromised individuals, such as those with HIV/AIDS, symptoms can be severe, life threatening, and recurring. T. gondii infection of a fetus or newborn can also cause severe neurological impairment, blindness, mental retardation , and death. When a fetus acquires the infection through its mother, this is called congenital toxoplasmosis.

Transmission

The organism that causes toxoplasmosis can be transmitted in four ways. The most common way is through contact with feces of an infected cat. Cats, the primary carriers of the organism, become infected by eating rodents and birds infected with T. gondii. Once ingested, the organism reproduces in the intestines of the cat, producing millions of eggs known as oocysts. These oocysts are excreted in cat feces daily for approximately two weeks. In the United States, approximately 50 percent of cats have been infected with T. gondii.

Oocysts are not capable of producing infection until approximately 24 hours after being excreted in warm climates and longer in cold climates. However, they remain infective in water or moist soil for about one year. Humans become infected when they come in contact with and accidentally ingest oocysts when changing cat litter, playing in contaminated sand, working in the garden or similar activities, or by eating unwashed vegetables and fruit irrigated with untreated water that has been contaminated with cat feces.

The second way humans become infected with T. gondii is through eating raw or undercooked meat. When cattle, sheep, or other livestock forage through areas contaminated with cat feces, these animals become carriers of the disease. The organism forms cysts in the muscle and brain of the livestock. When humans eat raw or undercooked infected meat, the walls of the cysts are broken down in the human digestive tract, and the individual becomes actively infected. The encysted organism can be killed by freezing or cooking the meat well.

The only form of direct person-to-person transmission occurs from mother to fetus during pregnancy. This transmission occurs only if the mother is in the acute, or active, stage of infection when the organism is circulating in the mother's blood. It is estimated that about one third of women with active infections pass the infection along to their fetus. Women who have become infected six months or more before conception do not pass the infection on to their fetus, because the organism has become dormant (inactive) and formed thick-walled cysts in muscle and other tissues of the body. Reactivation of the infection in healthy individuals is extremely rare. Women who give birth to one infected child do not pass the infection to their fetus during subsequent pregnancies unless they are immunocompromised (for example, with AIDS ) and the infection recurs.

Finally, individuals can also become infected through blood and organ transplant from an infected person.

Demographics

Men and women of all races are equally affected by T. gondii, however, except for immunocompromised individuals, the implications are more serious for women, as they can pass the infection on to their offspring. The rate of infection in the United States varies considerably with location. Studies have found that the infection rate in women of childbearing age ranges from 30 percent in Los Angeles to 3.3 percent in Denver. Varying sanitary conditions and culinary habits, such as eating raw meat, account for some of this variation. The rate of infection increases with the age of the individual. About 3,500 to 4,000 children are born in the United States each year with congenital toxoplasmosis. Outside the United States, fetal infection rates tend to be higher, although the number of babies born with congenital toxoplasmosis was as of 2004 declining worldwide.

Causes and symptoms

In fetuses, the severity of infection is dependent on the time of transmission. Fetuses who acquire the infection during the first trimester of pregnancy often are still-born or die shortly after birth. Fetuses who acquire the infection late in pregnancy often show no symptoms when born.

Severe infections lead to seizure disorders, neurological disorders, abnormal muscle tone, deafness, partial or complete blindness caused by a condition called chorioretinitis, and mental retardation. These conditions may not be present at birth, especially if the infection occurred late in pregnancy. Vision deficits, especially, tend to show up later in life.

Young children can acquire toxoplasmosis in the same ways as adults. However, symptoms and complications when the disease is acquired after birth tend to be much milder than with congenital toxoplasmosis.

Children and adults with weakened immune systems have a high risk of developing serious symptoms, including cerebral toxoplasmosis, an inflammation of the brain (encephalitis ), one-sided weakness or numbness , mood and personality changes, vision disturbances, muscle spasms , and severe headaches. If untreated, cerebral toxoplasmosis can lead to coma and death.

When to call the doctor

Women who believe they may have become infected shortly before conception or during pregnancy should call their doctor immediately. Treatment is possible during pregnancy. Symptoms in the newborn may be obvious during the newborn examination. If they are not, parents should consult their doctor if they feel their child has any neurological or vision complications or is not meeting appropriate developmental milestones.

Diagnosis

A diagnosis of toxoplasmosis is made based on clinical signs and supporting laboratory results, including visualization of the organism in body tissue or isolation in animals. Blood tests for toxoplasmosis are designed to detect increased amounts of a protein or antibody produced in response to infection with T. gondii. Antibody levels can be elevated for years, however, even when the disease is in a dormant state. Amniocentesis (sampling amniotic fluid) between 20 and 24 weeks of gestation can detect toxoplasmosis in the fetus.

Treatment

Most healthy individuals who contract toxoplasmosis do not require treatment, because the healthy immune system is able to control the disease. Symptoms are not usually present. Mild symptoms may be relieved by taking over-the-counter medications, such as acetaminophen (Tylenol) and ibuprofen (Motrin, Advil). Sore throat lozenges and rest may also ease the symptoms.

The benefits of treating women who contract toxoplasmosis during pregnancy almost always outweigh any risks involved. Treatment is with antibiotic and antimicrobial drugs. Transmission of toxoplasmosis from the mother to the fetus may be prevented or reduced if the mother takes the antibiotic spiramycin. Later in a pregnancy, if the fetus has contracted the disease, treatment with the antibiotic pyrimethamine (Daraprim, Fansidar) and folinic acid (an active form of folic acid ) may be effective. Babies born with toxoplasmosis who show symptoms of the disease may be treated with pyrimethamine, the sulfa drug sulfadiazine (Microsulfon), and folinic acid. Healthy children over the age of five usually do not require treatment. Infected individuals with weakened immune systems may require lifetime drug treatment to keep the infection from recurring.

Prognosis

The prognosis is poor when congenital toxoplasmosis is acquired during the first three months of pregnancy. Afflicted children die in infancy or suffer damage to their central nervous systems that can result in physical and mental retardation. Infection later in pregnancy often results in only mild symptoms, if any. The prognosis for acquired toxoplasmosis in adults with strong immune systems is excellent. The disease often disappears by itself after several weeks. However, the prognosis for immunodeficient patients is not as positive. These patients often relapse when treatment is stopped. The disease can be fatal to all immunocompromised patients, especially individuals with AIDS, and particularly if not treated.

Prevention

There are no drugs that can eliminate T. gondii cysts in animal or human tissues. Humans can reduce their risks of developing toxoplasmosis by practicing the following measures:

• freezing foods (to 10.4°F/–12°C) and cooking foods to an internal temperature of 152°F/67°C to kill the cysts
• practicing sanitary kitchen techniques, such as washing utensils and cutting boards that come into contact with raw meat
• keeping pregnant women and children away from household cats and cat litter
• disposing of cat feces daily because the oocysts do not become infective until after 24 hours
• helping cats to remain free of infection by feeding them dry, canned, or boiled food and by discouraging hunting and scavenging
• washing hands after outdoor activities involving soil contact and wearing gloves when gardening

Parental concerns

Fear of infection during pregnancy is the most common parental concern. When a fetus is found early in pregnancy to be infected, parents are faced with the decision of whether to continue the pregnancy given the likelihood of serious complications to the fetus.

KEY TERMS

Cyst —An abnormal sac or enclosed cavity in the body filled with liquid or partially solid material. Also refers to a protective, walled-off capsule in which an organism lies dormant.

Immunocompromised —A state in which the immune system is suppressed or not functioning properly.

Oocyst —A developmental stage of certain parasitic organisms, including those responsible for malaria and toxoplasmosis, in which the zygote of the organism is enclosed in a cyst.

Resources

BOOKS

Ambrose-Thomas, P., et al. Congenital Toxoplasmosis: Scientific Background, Clinical Management, and Control. New York: Springer, 2000.

Joynson, David H. M., et al. Toxoplasmosis: A Comprehensive Clinical Guide. Cambridge, UK: Cambridge University Press, 2001.

PERIODICALS

Jones, J. "Congenital Toxoplasmosis." American Family Physician 67 (May 15, 2003): 2131–8.

WEB SITES

Leblebicioglu, Hakan, and Murat Hökelek. "Toxoplasmosis." eMedicine.com August 10, 2004. Available online at <www.emedicine.com/ped/topic2271.htm> (accessed October 15, 2004).

The Merck Manual of Diagnosis and Therapy, 17th ed. Edited by Mark Beers and Robert Berkow. Available online at <www.merck.com/mrkshared/mmanual/home.jsp> (accessed October 15, 2004).

Tish Davidson, A.M.

Toxoplasmosis

Definition

Toxoplasmosis is an infectious disease caused by the one-celled protozoan parasite Toxoplasma gondii. Although most individuals do not experience any symptoms, the disease can be very serious, and even fatal, in individuals with weakened immune systems.

Description

Toxoplasmosis is caused by a one-celled protozoan parasite known as Toxoplasm a gondii. Cats, the primary carriers of the organism, become infected by eating rodents and birds infected with the organism. Once ingested, the organism reproduces in the intestines of cats, producing millions of eggs known as oocysts, which are excreted in cat feces daily for approximately two weeks. In the United States, it is estimated that approximately 30% of cats have been infected by T. gondii. Oocysts are not capable of producing infection until approximately 24 hours after being excreted, but they remain infective in water or moist soil for approximately one year. When cattle, sheep, or other livestock forage through areas with contaminated cat feces, these animals become carriers of the disease. Fruits and vegetables can also become contaminated when irrigated with untreated water that has been contaminated with cat feces. In humans and other animals, the organisms produce thick-walled, dormant structures called cysts in the muscle and other tissues of the body.

Most humans contract toxoplasmosis by eating cyst-contaminated raw or undercooked meat, vegetables, or milk products. Humans can also become infected when they come into contact with the T. gondii eggs while cleaning a cat's litterbox, gardening, or playing in a sandbox, for instance. Once infected, an individual is immune to reinfection. The incubation period or period between infection and the start of the disease ranges from several days to months.

Anyone can be infected by T. gondii, but usually only those individuals with weakened immune systems (immunocompromised) develop symptoms of the disease. For them, toxoplasmosis can be severe, debilitating, and fatal. Immunocompromised individuals at risk include those with AIDS, cancer, or other chronic illnesses.

There is no person-to-person transmission, except from an infected mother to her child in the womb. Approximately six out of 1,000 women contract toxoplasmosis during pregnancy. Nearly half of these maternal infections are passed on to the fetus. Known as congenital toxoplasmosis, this form of the disease is acquired at birth by approximately 3,300 infants in the United States every year. The risk of fetal infection is estimated to be between one in 1,000 to one in 10,000. In children born with toxoplasmosis, symptoms may be severe and quickly fatal, or may not appear until several months or even years after birth.

Causes and symptoms

Healthy individuals do not usually display symptoms. When symptoms do occur, they are usually mild, resembling infectious mononucleosis, and include the following:

• enlarged lymph nodes
• muscle pains
• intermittent fever
• general sick feeling

The distinction is made between acquired toxoplasmosis, in which an individual becomes infected, and neonatal congenital toxoplasmosis, in which a fetus is born with the infection because the mother became infected during pregnancy. If a fetus becomes infected early in pregnancy, the disease can cause the fetus to spontaneously abort, be stillborn. If full-term, the infant may die in infancy or suffer from central nervous system lesions. If the mother becomes infected in the last three months of pregnancy, however, the prognosis is good and the baby may not even display any symptoms.

In adults, if the infection continues for an extended period of time, chronic toxoplasmosis can cause an inflammation of the eyes called retinochoroiditis, which can lead to blindness, severe yellowing of the skin and whites of the eyes (jaundice ), easy bruising, and convulsions.

Adults with weakened immune systems have a high risk of developing cerebral toxoplasmosis, including inflammation of the brain (encephalitis ), one-sided weakness or numbness, mood and personality changes, vision disturbances, muscle spasms, and severe headaches. If untreated, cerebral toxoplasmosis can lead to coma and death. This form of encephalitis is the second most common AIDS-related nervous system infection that takes advantage of a person's weakened immune system (opportunistic infection).

Diagnosis

A diagnosis of toxoplasmosis is made based on clinical signs and supporting laboratory results, including visualization of the protozoa in body tissue or isolation in animals and blood tests. Laboratory tests for toxoplasmosis are designed to detect increased amounts of a protein or antibody produced in response to infection with the toxoplasmosis organism. Antibody levels can be elevated for years, however, without active disease.

Treatment

Most individuals who contract toxoplasmosis do not require treatment because their immune systems are able to control the disease. Symptoms are not usually present. Mild symptoms may be relieved by taking over-the-counter medications, such as acetaminophen (Tylenol) and ibuprofen (Motrin, Advil). Sore throat lozenges and rest may also ease the symptoms.

Although the treatment of women infected with toxoplasmosis during pregnancy is controversial, most physicians feel that treatment is justified. Transmission of toxoplasmosis from the mother to the fetus may be prevented if the mother takes the antibiotic spiramycin. Later in a pregnancy, if the fetus has contracted the disease, treatment with the antibiotic pyrimethamine (Daraprim, Fansidar) or sulfonamides may be effective. Babies born with toxoplasmosis who show symptoms of the disease may be treated with pyrimethamine, the sulfa drug sulfadiazine (Microsulfon), and folinic acid (an active form of folic acid ).

AIDS patients who have not been infected may be given a drug called TMP/SMX (Bactrim or Septra) to prevent toxoplasmosis infection. To treat cases of toxoplasmosis in immunocompromised AIDS patients, a combination of pyrimethamine and a sulfa-based drug, either sulfadiazine or clindamycin (Cleocin), have been used together and can be effective in treating this disease. Other antibiotic combinations and dosing schedules are still being investigated. Physicians have reported success in alleviating symptoms by using trimethoprim-sulfamethoxazole (Proloprim or Trimpex) or dapsone (DDS) plus pyrimethamine. These drugs can produce side effects, such as allergic reaction, itching, rashes;, and nausea and patients must be monitored closely.

KEY TERMS

Cyst— The thick-walled dormant form of many organisms.

Immunocompromised— A state in which the immune system is suppressed or not functioning properly.

Oocyst— The egg form of the toxoplasmosis organism.

Protozoan— A single-celled, usually microscopic, organism.

Prognosis

The prognosis is poor when congenital toxoplasmosis is acquired during the first three months of pregnancy. Afflicted children die in infancy or suffer damage to their central nervous systems that can result in physical and mental retardation. Infection later in pregnancy usually results in only mild symptoms, if any. The prognosis for acquired toxoplasmosis in adults with strong immune systems is excellent. The disease often disappears by itself after several weeks. However, the prognosis for immuniodeficient patients is not as positive. These patients often relapse when treatment is stopped. The disease can be fatal to all immunocompromised patients, especially AIDS patients, and particularly if not treated. As a result, immunocompromised patients are typically placed on anti-toxoplasmosis drugs for the rest of their lives.

Prevention

There are no drugs that can eliminate T. gondii cysts in animal or human tissues. Humans can reduce their risks of developing toxoplasmosis by practicing the following:

• freezing (to 10.4°F/−12°C) and cooking foods to an internal temperature of 152°F/67°C will kill the cyst
• practicing sanitary kitchen techniques, such as washing utensils and cutting boards that come into contact with raw meat
• keeping pregnant women and children away from household cats and cat litter
• disposing of cat feces daily, because the oocysts do not become infective until after 24 hours
• helping cats to remain free of infection by feeding them dry, canned, or boiled food and by discouraging hunting and scavenging
• washing hands after outdoor activities involving soil contact and wearing gloves when gardening

Resources

PERIODICALS

Rose, I. "Morphology and Diagnostics of Human Toxoplasmosis." General & Diagnostic Pathology 142 (June 1997): 257-70.

TOXOPLASMOSIS

Toxoplasmosis is an infection caused by a single-celled protozoan parasite named Toxoplasma gondii found throughout the world in humans, mammals, and birds. Cats, the definitive host for T. gondii, usually become infected by eating infected prey, and are the only animal that sheds the organism (as oocysts) in their feces. Animals other than cats are usually infected by ingesting oocysts in the soil or by eating infected animals.

Humans can become infected with T. gondii by one of three main routes: (1) by eating raw or inadequately cooked meat that contains T. gondii cysts (bradyzoites) or by eating uncooked foods that have come in contact with infected meat via, for example, cutting boards or cooking utensils;(2) by inadvertently ingesting oocysts that cats have passed in their feces either from a cat litter box or from soil (for example, from gardening) or by eating unwashed fruits and vegetables; (3) a newly infected woman can transmit the infection to her fetus.

Toxoplasmosis in adults usually does not cause symptoms, or causes only mild, nonspecific symptoms such as fever and swelling of the lymph glands. Therefore, the diagnosis is usually made by testing for antibodies that are produced in reaction to T. gondii infection. However, serious illness can occur when a newly infected woman passes the infection to her unborn fetus. Such an infection can lead to an infant with mental retardation, blindness, or other neurologic disorders. An estimated 400 to 4,000 congenital infections with T. gondii occur in the United States each year. Serious illnesses, including infection of the brain, can also occur in persons who have either old (latent) or new T. gondii infections when they do not have normal immune system function. Such persons include those with human immunodeficiency virus (HIV) infection or congenital immune illnesses, persons taking drugs that decrease immune system function, and persons with some types of cancer.

Effective means of preventing toxoplasmosis are as follows: (1) cook meat fully (internal temperature of 160° F) before eating it; (2) peel or wash fruits and vegetables before eating them; (3) wash hands, kitchen tools, counters, and sinks with soap and water after they have touched raw meat or unwashed fruits or vegetables; (4) clean the cat litter box every day so T. gondii oocysts do not have time to become infectious (one to five days); (5) wear gloves and wash hands after changing cat litter (pregnant women should not change cat litter if at all possible); (6) keep cats indoors so they do not become infected by eating prey; (7) feed cats only commercially prepared cat food, never undercooked or raw meat; and (8) wear gloves when gardening and wash hands after contact with soil and sand with which cats may have had contact.

Jeffrey L. Jones

(see also: Communicable Disease Control )

Bibliography

Centers for Disease Control and Prevention (1999). "1999 USPHS/IDSA Guidelines for the Prevention of Opportunistic Infections in Persons Infected with Human Immunodeficiency Virus: U.S. Public Health Service (USPHS) and Infectious Disease Society of America (IDSA)." Morbidity and Mortality Weekly Report 48(RR-10):7–9.

—— (2000). "CDC Recommendations Regarding Selected Conditions Affecting Women's Health: Preventing Congenital Toxoplasmosis." Morbidity and Mortality Weekly Report 49(RR-2):57–76.

Dubey, J. P. (1994). "Toxoplasmosis." Journal of the American Veterinary Medical Association 205:1593–1598.

Frenkel, J. K., and Fishback, J. L. (2000). "Toxoplasmosis." In Hunter's Tropical Medicine and Emerging Infectious Diseases, 8th edition, ed. G. T. Strickland. Philadelphia, PA: W. B. Saunders Company.

Toxoplasmosis

Toxoplasmosis is an infectious disease caused by the protozoan Toxoplasma gondii. The infection results from a parasitic association with a human host.

Cats are the primary carrier of the protozoan Toxoplasma gondii. In the United States, approximately 30% of cats are at some time infected by Toxoplasma gondii. Cattle, sheep, or other livestock can also excrete a form of the protozoan known as an oocyst. Although oocysts are not capable of producing an infection, they are important because they act to preserve the infectious capability of the protozoan during exposure to inhospitable environments. In this capacity they are analogous to the bacterial spore. Oocysts are often capable of resuscitation into the infectious form after prolonged periods of exposure to adverse environments.

Humans can also become infected by eating fruits and vegetables that have themselves become contaminated when irrigated with untreated water contaminated with oocyte-containing feces.

Humans typically contract toxoplasmosis by eating cyst-contaminated raw or undercooked meat, vegetables, or milk products. The protozoan can also be spread from litter boxes or a sandbox soiled with cat feces. In all cases, the agent that is ingested can be the inactive oocyst or the actively growing and infectious egg form of the parasite.

In the human host, the parasite is able to grow and divide. This causes the symptoms of the infection.

Symptoms of toxoplasmosis include a sporadic and reoccurring fever, muscle pain, and a general feeling of malaise. Upon recovery, a life-long immunity is conferred. In some people, the disease can become chronic and cause an inflammation of the eyes, called retinochoroiditis, that can lead to blindness, severe yellowing of the skin and whites of the eyes (jaundice), easy bruising, and convulsions. As well inflammation of the brain (encephalitis), one-sided weakness or numbness, mood and personality changes, vision disturbances, muscle spasms, and severe headaches can result.

Person to person transmission is not frequent. Such transmission occurs only during pregnancy. Some six out of 1,000 women contract toxoplasmosis during pregnancy. Nearly half of these infections are passed on to the fetus. Congenital toxoplasmosis afflicts approximately 3,300 newborns in the United States each year. In such children, symptoms may be severe and quickly fatal, or may not appear until several months, or even years, after birth.

As for many other microbial diseases, the observance of good hygiene (including appropriate hand washing protocols) is a key means of preventing toxoplasmosis.

See also Immunodeficiency diseases; Protozoa; Zoonoses