Human herpesvirus 8 (Kaposi sarcoma virus)

HHV-8 Virology - The Purple Cancer Virus

• Family: Herpesviridae (Gammaherpesvirinae subfamily).
• Structure: Enveloped, icosahedral capsid with a linear double-stranded DNA (dsDNA) genome.
• Cell Tropism: Primarily targets B lymphocytes and vascular endothelial cells.
• Latency: Establishes lifelong latency, primarily in B cells. The Latency-Associated Nuclear Antigen (LANA) tethers the viral episome to host chromosomes, ensuring its persistence during cell division.

⭐ HHV-8 encodes viral homologs of host regulatory proteins (e.g., v-cyclin, v-BCL-2, v-IL-6) that promote uncontrolled cell proliferation and angiogenesis while evading apoptosis.

Pathogenesis - Angiogenic Hijacker

• Primary Targets: Infects B-lymphocytes, but pathogenesis is driven by infection of vascular & lymphatic endothelial cells.
• Molecular Piracy: Establishes latency & expresses viral proteins that mimic host molecules to drive cell growth & survival:
  • v-Cyclin: Pushes cell cycle forward (G1→S).
  • v-IL-6: Pro-inflammatory & pro-growth cytokine.
  • v-BCL-2: Anti-apoptotic.
• Angiogenesis: Secretes viral Growth Factors (vGF) that are homologs of VEGF, directly stimulating neovascularization.

⭐ vGPCR: A viral G-protein coupled receptor is constitutively active, a key driver of VEGF secretion & proliferation.

Kaposi Sarcoma - The Classic Lesion

• Progression: Begins as flat, painless patches → evolves into raised plaques & nodules.
• Appearance: Violaceous, purple, brown, or black lesions.
  • Often elliptical and may align with skin tension lines.
• Common Sites:
  • Lower extremities (classic type).
  • Face, oral cavity (hard palate), genitalia (AIDS-related).
• Histopathology:
  • Spindle cell proliferation (endothelial origin).
  • Neovascularization & slit-like vascular spaces with extravasated RBCs.

⭐ High-Yield: Lesions are often multifocal and can arise in different places simultaneously, rather than metastasizing in the traditional sense.

Associated Malignancies - Beyond the Skin

• Primary Effusion Lymphoma (PEL)

  • Rare, aggressive B-cell lymphoma lining body cavities.
  • Presents as malignant effusions (pleural, peritoneal, pericardial) without a solid tumor mass.
  • Strongly associated with immunosuppression (e.g., AIDS).
  • Often co-infected with Epstein-Barr Virus (EBV).

• Multicentric Castleman Disease (MCD)

  • A systemic lymphoproliferative disorder.
  • Driven by viral cytokine dysregulation, particularly viral IL-6 (vIL-6).
  • Symptoms: fever, weight loss, lymphadenopathy, splenomegaly.

⭐ High-Yield: Primary Effusion Lymphoma cells are typically CD45-positive, but negative for conventional B-cell markers like CD19 and CD20.

Diagnosis & Management - Detect & Defeat

• Diagnosis (Gold Standard):

  • Punch biopsy of a lesion.
  • Histology: Proliferating spindle cells, neovascularization, and red blood cell extravasation.
  • PCR for HHV-8 DNA in tissue confirms diagnosis.

• Management Strategy:

  • Treatment is tailored to the clinical subtype.

⭐ In AIDS-related KS, initiating HAART is the most crucial management step. Lesion regression often occurs as the CD4 count rises, sometimes without needing chemotherapy.

High‑Yield Points - ⚡ Biggest Takeaways

• HHV-8 is strongly associated with Kaposi sarcoma, a vascular tumor common in AIDS patients.
• Transmission occurs primarily through saliva and sexual contact.
• The virus infects endothelial cells, inducing angiogenesis and proliferation of spindle cells.
• Presents as painless, purplish nodules or plaques on the skin, oral mucosa, and viscera.
• Also linked to primary effusion lymphoma and multicentric Castleman disease.
• Diagnosis is confirmed by biopsy showing spindle cells and neovascularization.