Toxoplasma gondii - Toxoplasmosis

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
  • Cytomegalovirus
  • Herpes simplex virus
  • Rubella
  • Treponema pallidum
  • Parvovirus B19
  • Listeria monocytogenes
  • Lymphocytic choriomeningitis
  • Varicella-zoster virus

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)