DNA Viruses: Herpesviruses

DNA Viruses: Herpesviruses

DNA Viruses: Herpesviruses

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Herpesviruses Overview - The Latent Lurkers

  • Large, enveloped viruses; icosahedral capsid; linear dsDNA genome.
  • Unique: Proteinaceous tegument between capsid and envelope.
  • Hallmark: Establish lifelong latent infections; periodic reactivation. image

⭐ All herpesviruses are dsDNA, enveloped, establish latency, and are notorious for reactivation.

SubfamilyKey FeaturesLatency Site(s)Examples
Alpha (α)Fast-growing, cytolyticSensory gangliaHSV-1, HSV-2, VZV
Beta (β)Slow-growing, cytomegalicGlands, kidneys, lymphoreticular cellsCMV, HHV-6, HHV-7
Gamma (γ)Variable growth, lymphoproliferativeLymphoid tissueEBV, KSHV (HHV-8)

Alphaherpesviruses (HSV, VZV) - Rapid Raiders

  • Neurotropic, establish latent infections; cause vesicular lesions.
  • Common Dx: Tzanck smear (multinucleated giant cells), Cowdry type A intranuclear inclusions, PCR.
VirusDiseasesTransmissionLatency Site
HSV-1Oral/ocular lesions, encephalitis, labialisContact, salivaTrigeminal ganglia
HSV-2Genital/neonatal herpesSexual, perinatalSacral ganglia
VZVVaricella (chickenpox), Zoster (shingles)Respiratory, contactDRG/cranial ganglia

Tzanck smear showing multinucleated giant cells

⭐ Herpes Simplex Encephalitis (HSV-1) is the most common cause of sporadic viral encephalitis, characteristically affecting temporal lobes.

Betaherpesviruses (CMV, HHV-6/7) - Slow & Stealthy

  • Cytomegalovirus (CMV)

    • Targets: Monocytes, lymphocytes, epithelial cells.
    • Clinical: Congenital (microcephaly, deafness); Immunocompromised (retinitis, colitis, pneumonitis); Mononucleosis-like syndrome.
    • Dx: "Owl's eye" basophilic intranuclear inclusions; PCR.
    • 📌 CMV: Can Make Various problems (Congenital, Compromised hosts), Cells Massively Vacuolated (Owl's eye).
  • Human Herpesvirus 6 (HHV-6) & 7 (HHV-7)

    • Targets: T-lymphocytes.
    • Clinical: Roseola infantum (Exanthem subitum) - high fever followed by rash.
    • 📌 HHV-6: Roseola - Fever then Rash on 6th day (approx).

⭐ Cytomegalovirus (CMV) is the most common viral cause of congenital infections and a major pathogen in transplant recipients.

Gammaherpesviruses (EBV, KSHV) - Oncogenic Opportunists

Lymphotropic, establish latency, oncogenic, especially in immunosuppression.

FeatureEBV (HHV-4)KSHV (HHV-8)
Target CellsB-cells (CD21), epithelial cellsEndothelial cells, B-cells
Key DiseasesInfectious Mononucleosis, Burkitt's Lymphoma, Nasopharyngeal Ca, Oral Hairy LeukoplakiaKaposi's Sarcoma, Primary Effusion Lymphoma, Multicentric Castleman's
DiagnosisMonospot, Atypical lymphocytes (Downey), SerologyBiopsy, PCR (HHV-8 DNA), LANA-1 serology
📌 KSHV: Kaposi's Sarcoma Herpes Virus - Kisses goodbye to healthy skin in AIDS.

⭐ EBV infects B-lymphocytes via the CD21 receptor, causing infectious mononucleosis and various cancers.

Herpesvirus Dx & Rx - Herpes Busters

  • Dx: PCR (CSF, lesions), Serology (IgM/IgG), Tzanck smear (multinucleated giant cells).
  • Rx: Antivirals
    DrugMoA (Key Enzyme)Key IndicationsMajor Toxicities
    AcyclovirDNA pol (TK)HSV, VZVNephro, Neuro
    ValacyclovirAcyclovir prodrugHSV, VZVNephro, Neuro
    GanciclovirDNA pol (UL97)CMVMyelosuppression
    ValganciclovirGanciclovir prodrugCMVMyelosuppression
    FoscarnetDNA pol (direct)Res. HSV/CMVNephro, Electrolytes ↓
    CidofovirDNA pol (nucleotide)Res. CMVNephro (severe), Uveitis

📌 Acyclovir: A Cycle-ovir stops viral DNA cycle.

⭐ Foscarnet: pyrophosphate analog, directly inhibits DNA pol (no phosphorylation needed); for resistant strains.

High-Yield Points - ⚡ Biggest Takeaways

  • All herpesviruses are dsDNA, enveloped and establish lifelong latency.
  • HSV-1 (oral), HSV-2 (genital); VZV (chickenpox/shingles); Tzanck smear shows multinucleated giant cells.
  • CMV is the most common congenital infection with characteristic "owl's eye" inclusions.
  • EBV causes infectious mononucleosis and is linked to Burkitt's lymphoma & nasopharyngeal carcinoma.
  • HHV-6 causes Roseola infantum (exanthem subitum); HHV-8 causes Kaposi's sarcoma.
  • Acyclovir and its derivatives are key antivirals for HSV and VZV infections_

Practice Questions: DNA Viruses: Herpesviruses

Test your understanding with these related questions

What does a Tzanck smear in varicella-zoster virus infection typically show?

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Flashcards: DNA Viruses: Herpesviruses

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Which herpesvirus is associated with Castleman's disease?_____

TAP TO REVEAL ANSWER

Which herpesvirus is associated with Castleman's disease?_____

HHV-8

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