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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.


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).


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.


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.


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.


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



Rose, I. "Morphology and Diagnostics of Human Toxoplasmosis." General & Diagnostic Pathology 142 (June 1997): 257-70.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


a disease due to Toxoplasma gondii. The congenital form may be asymptomatic or may produce encephalomyelitis with cerebral calcification, chorioretinitis and blindness, and even death. The acquired form is of two types: lymphadenopathic toxoplasmosis, closely resembling mononucleosis, and disseminated toxoplasmosis, with lesions involving the lungs, liver, heart, skin, muscle, brain, and meninges. Chorioretinitis invariably occurs in the congenital form, and often in the chronic form.

The only effective treatment of toxoplasmosis is the combination of pyrimethamine (Daraprim) and sulfadiazine or triple sulfonamides given for a total of 30 days. Treatment is reserved for those who are not immunologically competent. Treatment during pregnancy will not eliminate congenital toxoplasmosis but it can minimize its effects.

Prevention of infection with the protozoan parasite is aimed at avoiding ingestion of infective cysts in raw meat and eliminating contact with cat feces. Mutton, pork, and goat meat are more likely to be contaminated than beef; however, all meats should be thoroughly cooked, cured, or smoked before ingestion. Careful handling and disposal of cat litter can reduce the possibility of contamination from the feces of a pet cat, but it is difficult to determine when the cat has become infected.
Life cycle of Toxoplasma gondii. From Mahon and Manuselis, 2000.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


Disease caused by the protozoan parasite Toxoplasma gondii, which can produce abortion in sheep, encephalitis in mink, and a variety of syndromes in humans. Prenatally acquired human infection can result in the presence of abnormalities such as microcephalus or hydrocephalus at birth, the development of jaundice with hepatosplenomegaly or meningoencephalitis in early childhood, or the delayed appearance of ocular lesions such as chorioretinitis in later childhood. Postnatally acquired human infections typically remain subclinical; if clinical disease does occur, symptoms include fever, lymphadenopathy, headache, myalgia, and fatigue, with eventual recovery, except in the immunocompromised patient in whom fatal encephalitis often develops.
Farlex Partner Medical Dictionary © Farlex 2012


n. pl. toxoplas·moses (-mō′sēz)
A disease caused by the protozoan Toxoplasma gondii, especially:
a. A congenital disease characterized by lesions of the central nervous system that can cause blindness and brain damage.
b. An acquired disease characterized by fever, swollen lymph nodes, and lesions in the liver, heart, lungs, and brain.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


Infectious disease An infection by Toxoplasma gondii which is either
1. Congenital–acquired transplacentally, often with major neurologic residua or.
2. Acquired Epidemiology Ingestion of inadequately cooked meats with T gondii-filled cysts, or due to exposure to feces of infected cats, which are the definitive hosts Clinical In immunocompetent Pts, infection is benign with transient lymphadenopathy–80% of primary infections are asymptomatic; in immunocompromised Pts, T gondii infection may be accompanied by necrotizing encephalitis, myocarditis, pneumonitis, with CNS involvement in ≥ 50% Treatment Clindamycin, pyrimethamine; in AIDS, azithromycin. See Congenital toxoplasmosis.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


A disease caused by the protozoan parasite Toxoplasma gondii, which can produce a variety of syndromes in humans. Prenatally acquired infection can result in abnormalities such as microcephalus or hydrocephalus at birth, jaundice with hepatosplenomegaly or meningoencephalitis in early childhood, or delayed ocular lesions such as chorioretinitis in later childhood. Postnatally acquired human infections typically remain subclinical; if clinical disease does occur, symptoms include fever, lymphadenopathy, headache, myalgia, and fatigue, with eventual recovery, except in the immunocompromised patient, in whom fatal encephalitis often develops.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


Infection with the single-celled, bow-shaped, microscopic organism Toxoplasma gondii , often acquired before birth or from domestic cats. Severe congenital infection may damage the nervous system and other organs and cause stillbirth, but most infections are symptomless. The organism may damage the RETINA and this damage may be progressive calling for treatment with steroid drugs and PYRIMETHAMINE. Toxoplasmosis is common in people with immune deficiency, as in AIDS.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005


An infectious disease caused by the protozoan Toxoplasma gondii. It occurs either as a congenital or as an acquired type. The congenital type is characterized by bilateral retinochoroiditis in which the fovea is frequently destroyed, resulting in loss of central vision, hydrocephalus, convulsions and encephalomyelitis. The acquired type varies in severity and so does the ocular involvement, the more common lesion being a nonspecific intraocular inflammation involving either the anterior or posterior segment of the eye.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann


Disease caused by the protozoan parasite Toxoplasma gondii, which can produce various syndromes in humans. Prenatally acquired human infection can result in presence of abnormalities such as microcephalus or hydrocephalus at birth, development of jaundice with hepatosplenomegaly or meningoencephalitis in early childhood, or delayed appearance of ocular lesions such as chorioretinitis in later childhood.
Medical Dictionary for the Dental Professions © Farlex 2012
References in periodicals archive ?
These data are in agreement with Soheilian et al., [15] who compared the efficacy of the classical treatment of ocular toxoplasmosis (pyrimethamine, sulfadiazine, and prednisolone) with a regimen consisting of trimethoprim/ sulfamethoxazole (cotrimoxazole) plus prednisolone.
The premise that putative infection by parasites with diverse virulence and/or atypical/recombinant genotypes leads to different manifestation of ocular toxoplasmosis was not confirmed by our parasitology team, as shown by Carneiro et al., 2013 [19].
Paris, "Comparison of immunoblotting, calculation of the goldmann-witmer coefficient, and real-time PCR using aqueous humor samples for diagnosis of ocular toxoplasmosis," Journal of Clinical Microbiology, vol.
Nuseenblatt R, Belfort Jr R, Ocular toxoplasmosis.JAMA.1994; 271: 302-307
T lymphocytes are needed for complete control of ocular toxoplasmosis. (15,16) These cells could produce both cytokines and lytic granules in attempt to eliminate the invading parasite, and BDNF to prevent retina damage.
To the Editor: Ocular toxoplasmosis (OT), caused by the parasite Toxoplasma gondii, is known to be a major health problem in South America, especially in Colombia and Brazil (1-3).
(17,18) Ocular toxoplasmosis is the second most common retinal infection in AIDS; the most common is due to CMV retinitis.
These findings suggest the potential of EDI-OCT in morphological characterization of the choroidal and retinal changes in ocular toxoplasmosis.