Is there a test for parvovirus B19 (Fifth disease)?

Testing for Parvovirus B19

Yes, multiple laboratory tests are available for parvovirus B19 diagnosis, with serologic testing (IgM and IgG antibodies) being the primary method for acute infection, and PCR-based molecular testing for detecting viral DNA in specific clinical scenarios. 1

Primary Diagnostic Approaches

Serologic Testing (First-Line)

IgM antibody testing is the standard approach for diagnosing acute parvovirus B19 infection. 1 The presence of B19-specific IgM indicates recent or acute infection and is typically detectable during the symptomatic phase of illness. 2

• IgG antibody testing is used to determine past infection or immunity status 1
• Both IgM and IgG can be detected using enzyme-linked immunosorbent assay (ELISA) methods 2, 3
• IgM antibodies may persist for 2-3 months after acute infection, though sensitivity decreases significantly in specimens collected more than 7 weeks after symptom onset 3

Important Limitations of Serologic Testing

• Commercial ELISA tests show variable sensitivity (79-84%) compared to research assays, particularly in late-stage infections 3
• IgM may be undetectable in immunocompromised patients despite active infection 4
• False-positive IgM results can occur with rubella infection, rheumatoid factor, or heterophil antibodies if less stringent cutoff criteria are used 3

Molecular Testing (PCR)

PCR detection of parvovirus B19 DNA is the preferred method for immunocompromised patients, fetal infections, and cases where serologic testing is unreliable. 1, 5

Clinical Scenarios Where PCR is Essential

• Immunocompromised patients: These individuals may have prolonged viremia without detectable antibody response 4
• Fetal infections: B19 DNA can be detected in cord blood, amniotic fluid, ascitic fluid, and fetal effusions 5
• Chronic infections: PCR can detect persistent low-level viremia for months (up to 10 months documented) 4
• Cardiac involvement: Quantitative PCR on endomyocardial biopsies or pericardial fluid can detect B19 in myocarditis or pericarditis cases 1

PCR Advantages Over Serology

• B19 DNA persists longer than IgM antibodies, extending the diagnostic window 5
• All specimens with confirmed IgM positivity also show B19 DNA by PCR 5
• Nested PCR techniques provide high sensitivity for detecting low viral loads 1
• Quantitative PCR (real-time PCR) can measure viral loads ranging from 50 to 500,000 copies/μg in cardiac tissue 1

Specialized Testing Approaches

Immunoblot Testing

Immunoblot assays using viral capsid proteins (VP1, VP2) and nonstructural protein (NS1) can resolve equivocal ELISA results and detect late-stage infections. 2

• IgG immunoblots with strong reaction bands may indicate recent infection even when IgM is low or absent 2
• Useful for diagnosing chronic arthritis or hydrops fetalis where IgM has disappeared 2
• Can identify false-positive ELISA results 2

Tissue-Based Testing

For suspected cardiac involvement (myocarditis, pericarditis, or cardiomyopathy):

• Comprehensive workup requires histological, immunohistological, and molecular investigations of pericardial fluid and peri/epicardial biopsies 1
• Parvovirus B19 DNA is frequently detected at high copy numbers (up to 7 × 10⁶ genome equivalents/μg DNA) in epicardial tissue 1
• PCR on endomyocardial biopsy specimens can detect B19 in patients with dilated cardiomyopathy or unexplained ventricular dysfunction 1

Common Pitfalls and Caveats

• Serology is futile for diagnosing viral pericarditis—molecular and histological methods on tissue are required for definitive diagnosis 1
• Negative PCR does not exclude viral disease due to sampling error in focal infections and uncertain sensitivity 1
• Commercial antibody tests may miss infections detected by more sensitive research assays 3, 6
• In immunocompromised children, 45% may have detectable B19 DNA while only 25% have IgG antibodies, indicating frequent infection without adequate immune response 4
• Transfusion of blood products is a potential route of B19 transmission in immunocompromised patients 4

Practical Testing Algorithm

For immunocompetent patients with suspected acute infection:

• Start with B19-specific IgM and IgG ELISA 1
• If IgM is equivocal or low-titer, consider immunoblot confirmation 2
• PCR testing if symptoms persist beyond 7 weeks with negative or equivocal serology 3

For immunocompromised patients:

• Proceed directly to PCR testing as antibody response may be absent or delayed 4
• Serial PCR monitoring may be needed to detect persistent infection 4

For suspected fetal infection or cardiac involvement:

• PCR on appropriate specimens (amniotic fluid, fetal effusions, or cardiac tissue/pericardial fluid) is essential 1, 5
• Serology alone is insufficient for these presentations 1