An Every Person's Guide to HIV and Toxoplasmosis

Common Parasitic Infection Potentially Life Threatening in People with HIV

Used under a Creative Commons license at
Toxoplasma gondii oocysts. Photograph © Yale Rosen

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 Centers for Disease Control and Prevention.

It is estimated that around 22% of the U.S. population is infected with T. gondii. Over 200,000 cases of are reported each year, resulting in nearly 750 deaths—making it the second most common cause of lethal food-borne disease behind Salmonella poisoning.

Incidence rates in Africa, Southeast Asia, Latin American, and parts of Central and Eastern Europe can run well in excess of 50%.

Since the 1980s, there has been a steep decline in T. gondii infections in the U.S., due primarily to radical changes in farming systems and food safety management. Additionally, the risk of toxoplasmosis has dropped among people living with HIV as a result of effective antiretroviral therapy and the use ofprophylactic medication that can better prevent the development of T. gondii infection.

Modes of Transmission

T. gondii can infect most warm-blooded creatures, but is particularly prevalent in cats. Transmission is most frequently caused by:

  • Hand-to-mouth contact with surfaces or items that have been contaminated with cat feces or kitty litter
  • Eating T. gondii-infected meat
  • Transmission from mother to child during pregnancy

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 neramage, 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 pneumonia). In severe cases, toxoplasmosis can spread beyond the brain and lungs to 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 impairment. While most newborns infected with T. gondii will appear asymptomatic, symptoms are likely to develop in later years.

One recent study by Case Western Reserve University showed that, in women with advanced HIV infection, there was a three-fold increase in risk of transmission from mother to child.

Diagnosis of Toxoplasmosis

Diagnosis of toxoplasmosis is supported by a review of clinical features and symptoms, alongside the analysis of blood or tissue samples. A simple genetic test called the PCR (polymerase chain reaction) can be used to detect the presence of T. gondii antibodies in blood or other body fluids.

(In the event of recent infection, a PCR may not be able to detect T. gondii antibodies for up to eight weeks. During this so-called window period, a series of PCRs may be required to confirm infection, performed at 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

In 2015, the manufacturer of the drug Daraprim (Turing Pharmaceuticals) was mired  in controversy after its CEO, Martin Shkreli, tried to raise the price by 5000%, from $13.50 per tablet to $750 per tablet.

Prevention of T. gondii Infection

In severely immune comprised individuals (CD4 counts of less than 100) or pregnant women with HIV, special precautions may be advised to reduce the risk of T. gondii infection. These include:

  • Having someone else change the kitty litter or wearing a pair of disposable gloves when doing so yourself. Thoroughly wash your hands afterwards, and do not store your kitty box in or near the kitchen. If possible, keep your cat indoors.
  • Cooking foods to safe temperatures, while ensuring that meat is not pink and that juices run clear. Peel and wash fruits and vegetables whenever possible.
  • Wearing gloves whenever gardening or working with soil, thoroughly washing your gloves and hands when finished.

Pronunciation: TOK-so-plas-MOE-sis


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.

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.