• Toxoplasma gondii is an obligate intracellular protozoan parasite.
  • Most common latent protozoan infection
  • Clinically significant disease typically manifests only in pregnancy or in an immunocompromised patient.


  • Acute self-limited infection in immunocompetent individuals
  • Acute symptomatic or reactivated latent infection in immunocompromised patients
  • Congenital toxoplasmosis (acute primary infection during pregnancy)
  • Ocular toxoplasmosis

Pediatric Considerations

  • The earlier a fetal infection occurs, the more severe the resulting disease.
  • Risk of perinatal death is 5% if infected in 1st trimester.

Pregnancy Considerations

  • Pregnant immunocompromised and HIV-infected women should undergo serologic testing.
  • Counsel pregnant women regarding risks of toxoplasmosis.
  • Serologic testing during pregnancy is controversial.



  • Prevalence of congenital toxoplasmosis in the United States: 10 to 100/100,000 live births
  • Predominant sex: male > female


  • Present in every country with prevalence differing worldwide. Seropositivity rates range from <10% to >90% (1)[A] with overall seroprevalence declining (2).
  • In the United States, 11% of individuals aged 6 to 49 years are seropositive.
  • Age-adjusted prevalence in the United States is 10%.
  • Seroprevalence among women in the United States is 9%.
  • Increasing prevalence of IgG seropositivity with age as a result of cumulative seropositivity
  • Toxoplasmosis is considered a neglected parasitic infections in the United States and has been targeted by CDC for public health action.

Etiology and Pathophysiology

  • T. gondii has two life cycles. The sexual portion of the life cycle is exclusive to felines. The asexual cycle occurs in humans. Cats become infected by eating contaminated meat (birds, mice). Oocysts form within the tract of the cat and are shed in the stool.
  • Transmission to humans
    • Ingestion of raw or undercooked meat, food, or water containing tissue cysts or oocytes that is usually from soil contaminated with feline feces
    • Transplacental passage from infected mother to fetus; risk of transmission is 30% on average.
    • Blood product transfusion or solid-organ transplantation
    • Ingested T. gondii oocysts enter host’s gastrointestinal tract where bradyzoites/tachyzoites are released, penetrate contiguous cells, replicate, and are transported to susceptible tissues causing clinical disease.

Human leukocyte antigen (HLA) DQ3 is a genetic marker for susceptibility in HIV/AIDS patients.

Risk Factors

  • Immunocompromised states, including HIV infection with CD4 cell count <100/μL
  • Primary infection during pregnancy; risk of fetal transmission increases with gestational age at seroconversion. Transmission in the 1st trimester is associated with more severe consequences.
  • Chronically infected immunocompromised pregnant women are at increased risk for transmitting congenital toxoplasmosis.

General Prevention

  • Avoid eating undercooked meat: Cook to 152°F (66°C) or freeze for 24 hours at ≤−12°C.
  • Avoid drinking unfiltered water.
  • Wash produce thoroughly.
  • Wear gloves and wash hands after gardening and handling soil.
  • Wear gloves and wash hands after handling raw meat or cat litter.
  • Avoid shellfish (Toxoplasma cysts).

Commonly Associated Conditions

  • Chorioretinitis; self-limiting, febrile lymphadenopathy; mononucleosis-like illness
  • Potential association with schizophrenia

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