Toxoplasmosis is a topic covered in the 5-Minute Clinical Consult.

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  • 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
  • Acute symptomatic or reactivated latent infection in immunocompromised persons
  • Congenital toxoplasmosis (acute primary infection during pregnancy)
  • Ocular toxoplasmosis
Pediatric Considerations
  • The earlier fetal infection occurs, the more severe.
  • 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.
  • 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. Seropositivity rates range from <10% to >90% (1)[A].
  • In the United States, 11% of individuals aged 6 to 49 years are seropositive.
  • Age-adjusted prevalence in the United States is 23%.
  • Seroprevalence among women in the United States is 15%.

Etiology and Pathophysiology

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.
  • Strict hand hygiene after touching 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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