Can Chickenpox Cause a Positive Herpes Test?

February 28, 2024

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Chickenpox, caused by the varicella-zoster virus (VZV), is a common childhood illness characterized by an itchy rash and fever. After recovery, VZV remains dormant in the nerves and can reactivate later as shingles (herpes zoster). On the other hand, herpes simplex virus (HSV) has two types – HSV-1 causing oral herpes (cold sores) and HSV-2 causing genital herpes. Diagnostic testing can detect these viruses through blood tests, skin lesion cultures, or PCR.

But can a previous VZV infection from chickenpox lead to a false positive result on a herpes test?

The Short Answer

Yes, there is a possibility of VZV antibodies cross-reacting with HSV antigens in serological assays like ELISA or Western Blot. So chickenpox may cause a false positive blood test for herpes simplex viruses even if the person does not have oral or genital herpes. Confirmatory tests are needed to differentiate between previous VZV exposure versus true HSV infection.

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Similarities Between Varicella-Zoster Virus and Herpes Simplex Virus

  • Both VZV and HSV belong to the Herpesviridae family of double-stranded DNA viruses. They share similarities in viral structure and replication mechanisms.
  • After primary infection, both viruses establish lifelong latent infections in the sensory ganglia and can periodically reactivate.
  • Their capability for viral latency and reactivation is a key trigger for potential diagnostic confusion between chickenpox and herpes.

Limitations of Serological Testing

  • ELISA or Western Blot detect antibodies against whole virus antigens. So IgM/IgG antibodies targeting VZV proteins may cross-react with HSV proteins as well.
  • This cross-reactivity leads to false positive results, especially in blood tests relying on antibody-antigen binding.
  • Past resolved infection with the varicella-zoster virus can confound herpes simplex antibody testing.

Role of Confirmatory Testing

If serology suggests HSV exposure despite no symptomatic history, conduct further evaluations like:

  • HSV PCR or DFA testing on skin lesions
  • Type-specific glycoprotein G serology with higher specificity
  • Viral culture to demonstrate active HSV replication
  • Inquire about recent VZV reactivation or chickenpox exposure

Clinical Scenarios of Misdiagnosis

  • Childhood or recent chickenpox – Blood testing too soon after VZV infection
  • Prior clinical or subclinical VZV reactivation
  • Recent shingles diagnosis without hsv testing
  • History of varicella vaccination – Rare vaccine viral shedding

Takeaway Messages

  • Consider potential VZV antibody interference with HSV blood testing
  • Do not rely solely on serological screening to diagnose genital herpes
  • Follow-up equivocal herpes results with confirmatory PCR or DFA
  • Evaluate overall clinical picture with vaccination/exposure history

So while chickenpox does not directly cause herpes simplex infections, it can certainly impact the accuracy of diagnostic testing – yielding misleading positive results for HSV in some cases due to previous immune response against VZV.

Differentiating Between the Viruses

Varicella-Zoster VirusHerpes Simplex Virus
TransmissionAirborne spreadSkin-to-skin contact
Latency SiteDorsal root gangliaTrigeminal ganglia
Reactivation ConditionOld age, immunocompromised stateStress, sunlight, fatigue
Recurrent InfectionHerpes Zoster (Shingles)Oral & Genital Herpes
ComplicationsPostherpetic neuralgia, Vision lossNeonatal herpes, Encephalitis
Vaccine AvailableVaricella vaccineNo approved vaccine

Table 1. Comparison between varicella-zoster virus and herpes simplex virus

HSV-IgG Test Reliability Issues

  • Potential confusion with other prevalent viruses (CMV, VZV, HHV-6)
  • IgG tests often misclassify >15% of positive results
  • Regional variability in HSV-2 strains also impacts accuracy
  • WHO recommends against using HSV-2 IgG alone for diagnosis

Concluding Remarks

  • Clinical diagnosis should factor exposure/vaccination history
  • Do not solely rely on blood test suggesting HSV with no lesions
  • Confirm unusual positive results with type-specific glycoprotein antigens
  • Proceed cautiously in interpreting positive HSV IgG test
  • Even glycoprotein assays may misclassify 10% of samples


  • Chickenpox can mimic herpes simplex virus in serological assays
  • Cross-reactivity and non-type specific antibodies causes false positives
  • Further verification is needed with DFA, PCR or culture testing
  • Clinical history and physical examination still vital in diagnosis
  • Caution warranted in interpreting positive herpes blood test

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5 Key FAQs

What else can cause a positive herpes test?

Other viruses like varicella-zoster (chickenpox), cytomegalovirus (CMV), and HHV-6 can trigger antibodies cross-reacting with herpes antigens on blood tests. Recent vaccination or asymptomatic viral reactivation may also lead to detection of antibodies without actual herpes infection.

Is there a connection between chicken pox and herpes?

Yes, varicella-zoster virus has similarities with herpes simplex virus as both establish lifelong latent infections in nerve tissues. Prior chickenpox exposure generates antibodies that may recognize and bind to both VZV and HSV proteins on screening assays.

Can you test positive for herpes but never have an outbreak?

Yes, low positive results can detect antibodies from earlier subclinical exposures. Many may ignore remote herpes infection until faced with unexpected positive results despite no symptoms.

Will I test positive for herpes if I get cold sores?

Yes, those experiencing recurrent cold sores triggered by HSV-1 can definitely test positive for oral herpes. But about 80% of HSV-2 infections causing genital herpes do lead to observable symptoms so positive results fit with clinical history.

What can cause a false positive herpes test?

Cross-reactivity with prevalent viruses, technical errors in the assay procedure itself, variations in viral strains, and limitations of screening methods can all contribute to herpes misdiagnosis through false positive results.

Summary of Main Points

  • Chickenpox triggers antibodies cross-reacting with herpes blood tests
  • Serological screening has intrinsic limitations causing false positives
  • Confirm unusual positive test results with DFA staining or PCR assays
  • Clinical diagnosis should take exposure and vaccination history into account
  • Caution required when interpreting positive HSV test lacking lesions
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