Toxoplasma gondii

  • Diagnosis
  • Algorithms
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

  • Pregnant female with suspected exposure
  • Immunocompromised patient with undiagnosed flu-like illness

Laboratory Testing

  • Serology
    • Primary diagnostic method; recommend paired acute and convalescent antibody testing to confirm presence of disease
    • Pregnancy
      • IgG, IgM antibodies in pregnant women
        • Caution should be exercised in the use of IgM antibody levels due to lack of specificity in prenatal screening
          • Positive results in pregnant patients must be confirmed positive by a reference laboratory that specializes in toxoplasmosis
          • CDC recommends the Toxoplasma Serology Laboratory at Palo Alto Medical Foundation
          • If positive at reference lab, testing should be evaluated by amniocentesis and PCR testing for T. gondii
      • See the Toxoplasmosis Serologic Testing Algorithm for test result interpretation or the CDC's toxoplasmosis information page for serology result interpretation
      • As suggested by the CDC, any equivocal or positive result should be retested using a different assay (eg, Sabin-Feldman IgG dye test, IgM ELISA, IgA ELISA, IgG ELISA,  differential agglutination, avidity)
    • Suspected congenital toxoplasmosis – IgG and IgA by EIA
      • IgA more sensitive than IgM in congenitally infected infants
      • No commercial assay in the U.S. is cleared by the FDA for in vitro diagnostic use in infants
      • Specimens from neonates suspected of having congenital toxoplasmosis should be sent for testing by the Toxoplasma Serology Laboratory
    • Neonate – PCR on amniotic fluid
    • Immunocompromised – PCR
      • Serological determination of active central nervous system toxoplasmosis in immunocompromised patients is not possible at this time
      • Toxoplasma-specific IgG antibody levels in AIDS patients are often low to moderate and occasionally undetectable
      • Tests for IgM antibodies are generally negative
  • Cerebrospinal fluid exam
    • Not frequently performed because of increased central nervous system (CNS) pressure
    • Elevated protein, variable glucose, mildly elevated white blood cell count with mononuclear predominance
    • PCR for T. gondii may establish meningitis/encephalitis


  • Immunohistochemistry – T. gondii stain

Imaging Studies

  • CT/MRI of the brain in patients presenting with encephalitis

Differential Diagnosis

Toxoplasmosis is a zoonosis caused by the parasite Toxoplasma gondii, which infects both birds and mammals.


  • Incidence – 15-29% of U.S. population is seropositive for toxoplasmosis
    • Hot, arid climates have a low incidence of toxoplasmosis
  • Transmission
    • Usually oral
    • May occur via blood transfusion, organ transplant, or transplacentally from mother to infant


  • Obligate intracellular parasite
  • Cat is definitive host

Risk Factors

  • Predisposition to severe toxoplasmosis infection is common in persons with acquired immunodeficiency syndrome (AIDS) or in persons who are otherwise immunocompromised
  • Ingestion of raw or undercooked meat

Clinical Presentation

  • Nonimmunocompromised
    • Usually mild or asymptomatic disease in adults
    • Constitutional – prolonged fever, headache, lymph node enlargement, myalgias
    • Gastrointestinal – hepatomegaly, hepatitis
  • Pregnant females
    • Most women experience minimal symptoms
    • If immunocompromised, reactivation may occur – presents risk to fetus (rare vertical transmission)
  • Congenital
    • Risk of infection varies with gestational age
    • Symptoms range from asymptomatic to death
    • In infected neonates – chorioretinitis, encephalomyelitis, developmental delay, seizures, diffuse intracranial calcifications
    • Triad of chorioretinitis, hydrocephalus, brain calcification – highly suggestive of toxoplasmosis
  • Immunocompromised
    • Transplant patients – most common in heart transplant patients
    • HIV patients
      • Most common presentation is encephalitis – altered mental status, headache, fever, focal neurologic deficits
Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

Toxoplasma gondii Antibodies, IgG and IgM 0050521
Method: Semi-Quantitative Chemiluminescent Immunoassay

Toxoplasma gondii by PCR 0055591
Method: Qualitative Polymerase Chain Reaction

General References

Elmore SA, Jones JL, Conrad PA, Patton S, Lindsay DS, Dubey JP. Toxoplasma gondii: epidemiology, feline clinical aspects, and prevention. Trends Parasitol. 2010; 26(4): 190-6. PubMed

Khoshnood B, De Vigan C, Goffinet F, Leroy V. Prenatal screening and diagnosis of congenital toxoplasmosis: a review of safety issues and psychological consequences for women who undergo screening. Prenat Diagn. 2007; 27(5): 395-403. PubMed

Meroni V, Genco F. Toxoplasmosis in pregnancy: evaluation of diagnostic methods. Parassitologia. 2008; 50(1-2): 51-3. PubMed

Moncada PA, Montoya JG. Toxoplasmosis in the fetus and newborn: an update on prevalence, diagnosis and treatment. Expert Rev Anti Infect Ther. 2012; 10(7): 815-28. PubMed

Montoya JG, Remington JS. Management of Toxoplasma gondii infection during pregnancy. Clin Infect Dis. 2008; 47(4): 554-66. PubMed

Neu N, Duchon J, Zachariah P. TORCH infections. Clin Perinatol. 2015 Mar;42(1):77-103, viii. PubMed

Parasites - Toxoplasmosis (Toxoplasma infection) . Centers for Disease Control and Prevention. Atlanta, GA [Last updated Apr 2014; Accessed: Nov 2015]

Petersen E. Toxoplasmosis. Semin Fetal Neonatal Med. 2007; 12(3): 214-23. PubMed

Sensini A. Toxoplasma gondii infection in pregnancy: opportunities and pitfalls of serological diagnosis. Clin Microbiol Infect. 2006; 12(6): 504-12. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Martins TB, Hillyard DR, Litwin CM, Taggart EW, Jaskowski TD, Hill HR. Evaluation of a PCR probe capture assay for the detection of Toxoplasma gondii. Incorporation of uracil N-glycosylase for contamination control. Am J Clin Pathol. 2000; 113(5): 714-21. PubMed

Owen WE, Martins TB, Litwin CM, Roberts WL. Performance characteristics of six IMMULITE 2000 TORCH assays. Am J Clin Pathol. 2006; 126(6): 900-5. PubMed

Medical Reviewers

Last Update: October 2016