1. Health
You can opt-out at any time. Please refer to our privacy policy for contact information.

Discuss in my forum



Updated May 20, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Used under a Creative Commons license at http://www.flickr.com/photos/pulmonary_pathology/3785989291/

Toxoplasma gondii oocysts

Photograph © Yale Rosen

Definition: Toxoplasmosis is a parasitic disease caused by the protozoan Toxoplasma gondii (T. gondii). When it affects the brain (cerebral toxoplasmosis), it is considered an AIDS-defining condition by the U.S. Centers for Disease Control and Prevention (CDC).

Incidence Rates

In the U.S., approximately 22% of the population is infected with T. gondii. Incidence rates in Africa, Southeast Asia, Latin American, and parts of Central and Eastern Europe can run well in excess of 50%.

Over 200,000 cases of toxoplasmosis are reported in the U.S. each year, resulting in nearly 750 deaths—making it the second most common cause of lethal food-borne disease behind Salmonella.

That said, there has been a steep decline in T. gondii infections since the 1980s, due primarily to radical changes in farming systems and food safety management.

Additionally, the risk of toxoplasmosis has dropped among people with HIV as a result of effective antiretroviral therapy (ART) combined with prophylactic medication that can prevent the development of the disease.

Modes of Transmission

T. gondii can infect most warm-blooded creatures, but is particularly prevalent in cats. Transmission can be caused by accidentally ingesting feces from a cat (or kitty litter); by eating infected meat; or through prenatal transmission from mother to child. Breastfeeding is not considered a likely form of transmission.

Symptoms of Toxoplasmosis

In humans, the majority of infections are either asymptomatic or present with mild, flu-like symptoms, often accompanied by swollen lymph glands (lymphadenopathy). However, in immune compromised individuals—particularly HIV-infected persons with CD4 counts under 100 cells/µL-infection can be severe to deadly.

If left untreated, toxoplasmosis can cause severe encephalitis (inflammation of the brain) and retinal damage. The most common neurological signs are speech and motor impairment. In advanced disease, seizures, meningitis, optic nerve damage, and psychiatric manifestations are often seen.

Toxoplasmosis can also cause damage to the lungs, resulting in a sepsis-like inflammation and symptoms that are largely indistinguishable from PCP (Pneumocystis jiroveci carinii). Disseminated extracerebral toxoplasmosis can affect the liver, bone marrow and heart.

Toxoplasmosis in Pregnancy

T. gondii can cause devastating damage to developing fetuses, often resulting in lifelong mental and physical disabilities. While most newborns infected with T. gondii will appear asymptomatic, symptoms may likely to develop in later years.

One recent study by Case Western Reserve University showed that, in HIV-infected women who were severely immune compromised and had not received T. gondii prophylaxis, there was a three-fold increase in transmission risk from mother to child.

Diagnosis of Toxoplasmosis

Diagnosis of toxoplasmosis is supported by the presentation of clinical features and symptomatology; pre-test probability (a subjective assessment of the likelihood of infection in an individual); and the analysis of blood or tissue samples.

Serological tests can be performed to evidence infection, which can either amplify T. gondii DNA using PCR (polymerase chain reaction) technology, or detect the presence of T. gondii antibodies in blood or other body fluids.

(In the event of recent infection, serological tests may not be able to detect T. gondii antibodies for up to eight weeks. During this window period, a series of tests may be required, performed least three weeks apart.)

While a brain biopsy is considered the definitive diagnosis of cerebral toxoplasmosis, in recent years it has been largely replaced by a combination of an MRI or CT scanning to confirm the presence of brain lesions, followed by minimally invasive PCR testing.

Treatment of Toxoplasmosis

Treatment is recommended for HIV-positive persons with CD4 counts under 200, when the immune system is less able to fight infection. In these instances, Trimethoprin/sulfamethoxale (co-trimoxazole) is usually the drug of choice for prophylactic prevention.

For active disease, the following drugs may be prescribed:

  • A combination of Daraprim (pyrimethamine) and sulfadiazine (a sulfa-based antibiotic), plus folinic acid
  • Clindamycin (an antibiotic used to treat bacterial and protozoan infections)
  • Spiramycin (still considered experimental in U.S., although it can be obtained by special FDA permission during the first trimester of pregnancy)
  • Mepron (atavaquone)
  • A combination of Clindamycin and Meprone

Prevention of T. gondii Infection

In severely immune comprised persons with HIV (CD4s less than 100) or pregnant women with HIV, special precautions may be advised to reduce the risk of T. gondii infection. These include:

  • Have someone else change the kitty litter, or wear a pair of disposable gloves when doing so. Thoroughly wash your hands afterwards. If possible, keep your cat indoors. Do not store your kitty box in or near the kitchen.

  • Cook foods to safe temperatures, ensuring that meat is not pink and that juices run clear. Peel and wash fruits and vegetables, when possible.

  • Wear gloves whenever gardening or working with soil, thoroughly washing your gloves and hands when finished.


U.S. Centers for Disease Control and Prevention (CDC). "Toxoplasmosis (Toxoplasma Infection - Epidemiology and Risk Factors." Atlanta, Georgia; Global Health, Division of Parasitic Diseases and Malaria; January 10, 2012.

Bayarri, S.; Gracia, M.; Lázaro, R.; et al. "Toxoplasma gondii in Meat and Food Safety Implications - A Review." InTech. 2012: ISBN: 978-953-51-0479-7.

Oksenhendler, E.; Cadranel , J.; Sarfati, C.; et al. "Toxoplasma gondii pneumonia in patients with the acquired immunodeficiency syndrome." American Journal of Medicine. May 1990; 88(5):18-21.

Rabaud, C.; May, T.; Amiel, C.; et al. "Extracerebral toxoplasmosis in patients infected with HIV. A French National Survey." Medicine. November 1994; 73(6):306-314.

Oksenhendler, E.; Cadranel , J.; Sarfati, C.; et al. "Toxoplasma gondii pneumonia in patients with the acquired immunodeficiency syndrome." American Journal of Medicine. May 1990; 88(5):18-21.

Minkoff, H.; Remington, J.; Holman, S.; et al. "Vertical transmission of toxoplasma by human immunodeficiency virus-infected women." American Journal of Obstetrics and Gynecology. March 1997; 176(3):555-9.

Paquet, C. "Toxoplasmosis in pregnancy: prevention, screening, and treatment." Journal of Obstetrics and Gynecology. January 2013; 35(1): 78-79.


Pronunciation: TOK-so-plas-MOE-sis

©2014 About.com. All rights reserved.

We comply with the HONcode standard
for trustworthy health
information: verify here.