Toxoplasma gondii - Toxoplasmosis

Toxoplasmosis is a zoonosis caused by the parasite Toxoplasma gondii, an obligate intracellular parasite which infects both birds and mammals, including felines. Infection may cause no obvious symptoms in adults, but may be serious in pregnant women. Serology testing is the primary diagnostic method; acute and convalescent antibody testing is recommended to confirm the presence of disease.

Tabs Content

Clinical Overview

Diagnosis

Indications for Testing

Suspected exposure in pregnant female
Undiagnosed flulike illness in immunocompromised patient

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 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 polymerase chain reaction (PCR) testing for Toxoplasma 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 test (eg, Sabin-Feldman IgG dye test, IgM enzyme-linked immunosorbent assay [ELISA], IgA ELISA, IgG ELISA, differential agglutination, avidity)
- Suspected congenital toxoplasmosis – IgG and IgA by enzyme immunoassay (EIA)
  - IgA more sensitive than IgM in congenitally infected infants
  - No commercial test in the U.S. is cleared by the Food and Drug Administration (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 (CNS) 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 (CSF) exam
- Not frequently performed because of increased CNS pressure
- Elevated protein, variable glucose, mildly elevated white blood cell count with mononuclear predominance
- PCR for T. gondii may establish meningitis/encephalitis

Histology

Definitive diagnosis may require biopsy and pathologist examination
Useful immunohistochemical stain may include T. gondii stain
For detailed descriptions, refer to ARUP’s Immunohistochemistry Stain Offerings

Imaging Studies

Computed tomography (CT)/magnetic resonance imaging (MRI) of the brain in patients presenting with encephalitis

Differential Diagnosis

Flu-like presentation
- Bartonella spp
- Brucella spp
- Coxiella burnetii (Q fever)
- Ehrlichiosis
- Epstein-Barr virus
- Rickettsia spp
- Arbovirus
- Francisella tularensis
- Leptospira
CNS disease
- Malignancy
  - Primary CNS lymphoma
  - Primary brain tumor
  - Metastasis
- Viral/bacterial meningitis
- Encephalitis
- Demyelinating disease – multiple sclerosis
- Vasculitis
- Multifocal infarct
- Arteriovenous malformation
Congenital disease

Background

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

Risk Factors

Immunocompromised status, including AIDS
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 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
- Symptoms generally more severe
- HIV patients – most common presentation is encephalitis (altered mental status, headache, fever, focal neurologic deficits)

ARUP Lab Tests

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 enzyme-linked immunosorbent assay [ELISA], reflex to avidity and/or other tests)

Limitations

This test should not be used for blood donor screening, associated reentry 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

Medical Experts

Couturier, Marc Roger, PhD, D(ABMM), Medical Director, Microbial Immunology, Parasitology and Fecal Testing, and Infectious Disease Antigen Testing at ARUP Laboratories; Associate 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

References

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

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

U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Parasites - Toxoplasmosis (Toxoplasma infection). Centers for Disease Control and Prevention. Atlanta, GA [Last updated: Apr 2017; Accessed: Sep 2017]

Resources 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

Testing Algorithms

Toxoplasmosis Serologic Testing for Pregnant Women Algorithm

Read more about Toxoplasmosis Serologic Testing for Pregnant Women Algorithm

Last Update: May 2018

Toxoplasma gondii - Toxoplasmosis

Diagnosis

Indications for Testing

Laboratory Testing

Histology

Imaging Studies

Differential Diagnosis

Background

Epidemiology

Risk Factors

Clinical Presentation

ARUP Lab Tests

Medical Experts

References

General References

Resources from the ARUP Institute for Clinical and Experimental Pathology®

Toxoplasmosis Serologic Testing for Pregnant Women Algorithm

ARUP Laboratories

ARUP Websites

ARUP Consult


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	Toxoplasma gondii - Toxoplasmosis. ARUP Consult^©. Retrieved June 20, 2019, from: https://arupconsult.com/content/toxoplasma-gondii

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Toxoplasma gondii - Toxoplasmosis

Diagnosis

Indications for Testing

Laboratory Testing

Histology

Imaging Studies

Differential Diagnosis

Background

Epidemiology

Risk Factors

Clinical Presentation

ARUP Lab Tests

Medical Experts

References

General References

Resources from the ARUP Institute for Clinical and Experimental Pathology®

Toxoplasmosis Serologic Testing for Pregnant Women Algorithm

ARUP Laboratories

ARUP Websites

ARUP Consult