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

Histology

  • 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.

Epidemiology

  • 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

Organism

  • 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

Recommended Use 

First-line test for identifying visceral T. gondii infection

CDC suggests equivocal or positive results should be retested using a different assay from another reference laboratory specializing in toxoplasmosis testing (IgG dye test, IgM ELISA, reflex to avidity and/or other tests)

This test should not be used for blood donor screening, associated re-entry protocols, or for screening Human Cell, Tissues and Cellular and Tissue-Based Products (HCT/P)

Toxoplasma gondii by PCR 0055591
Method: Qualitative Polymerase Chain Reaction

Recommended Use 

Confirm toxoplasmosis infection in immunocompromised hosts as well as fetuses and newborns

May be used to confirm equivocal antibody testing

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

Couturier, Marc Roger, PhD, D(ABMM), Medical Director, Microbial Immunology, Parasitology and Fecal Testing, and Infectious Disease Rapid Testing at ARUP Laboratories; Assistant Professor of Clinical Pathology, University of Utah

Hillyard, David R., MD, Medical Director, Molecular Infectious Diseases at ARUP Laboratories; Professor of Clinical Pathology, Adjunct Professor of Biology, University of Utah

Arboviruses
Central Nervous System Tumors - Brain Tumors
Encephalitis, Infectious
Human Immunodeficiency Virus - HIV
Lymphomas, B-Cell - B-Cell Lymphomas
Lymphomas, T-Cell/NK-Cell - T-Cell/NK-Cell Lymphomas
Meningitis, Acute
Rickettsia typhi - Typhus Fever
Treponema pallidum - Syphilis
Vasculitis

Last Update: August 2016

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