HHV-6 and HHV-8

• Human Herpes Virus 6 (HHV-6) and Human Herpes Virus 8 (HHV-8) are double-stranded linear DNA viruses.

HHV-6

• Belongs to the Herpesviridae family, Betaherpesvirinae subfamily, and Roseolovirus genus.
• Transmitted through respiratory secretions.
• The virus attaches to dendritic cells, which present antigens to T cells.
• Migrates to lymph nodes, infecting CD4+ T lymphocytes where it replicates efficiently.
• Undergoes the lytic cycle within T cells, producing new viruses that destroy the cell and infect neighboring cells.
• Can also replicate in monocytes, macrophages, NK cells, astrocytes, megakaryocytes, and glial cells, but less efficiently.
• Enters a latent state in monocytes, potentially reactivating in immunocompromised individuals, causing serious infections like encephalitis.
• Primary infection causes roseola infantum (exanthem subitum or sixth disease).
• Common in children aged 6 months to 2 years.
• Incubation period: 1-2 weeks.
• Symptoms include high fever (up to 40°C or 104°F) lasting 3-5 days.
• Other symptoms of HHV-6 include peri-orbital edema, acute otitis media, rhinorrhea, cough, vomiting, diarrhea, bulging fontanelle, lymphadenopathy, Nagayama spots (erythematous papules on the soft palate and uvula).
• After fever subsides, a maculopapular rash appears on the neck, trunk, face, and extremities, lasting a few hours to two days.
• Diagnosis involves clinical findings, PCR to identify viral DNA, and serological tests for IgG antibodies against HHV-6.
• Treatment is supportive with antipyretics (acetaminophen or ibuprofen) and increased fluid intake.
• Antivirals like acyclovir or ganciclovir are used in severe cases (immunocompromised individuals).

HHV-8

• Also called Kaposi's sarcoma-associated herpesvirus (KSHV).
• Belongs to the human gammaherpesviruses family.
• It's one of the seven known oncoviruses (cancer-causing viruses), specifically causing Kaposi's sarcoma (KS).
• Large, double-stranded linear DNA virus with an icosahedral capsid, a protein layer called the tegument, and an envelope with viral glycoproteins.
• Transmitted through sexual contact.
• The virus enters B cells, endothelial cells, macrophages, and epithelial cells.
• In the latent phase, the virus remains in the cell without destroying it and expresses the latency-associated nuclear antigen (LANA-1).
• LANA-1 inhibits tumor suppressor protein p53, preventing apoptosis, leading to uncontrolled cellular proliferation.
• In the lytic phase, the virus replicates, producing new viruses that destroy the cell and infect neighboring cells.
• In healthy individuals, infection is rare due to humoral (antibodies) and cellular (cytotoxic T cells) immune responses.
• Immunocompromised individuals are at higher risk.
• Kaposi's sarcoma has four types: classic, endemic, epidemic (AIDS-associated), and immunosuppression therapy-related.
• Characterized by vascular proliferation and dark or violaceous plaques on the skin, mouth, GI tract, or lungs.
• Other symptoms include red or purple skin lesions resembling bruises, weight loss, nausea, vomiting, diarrhea, bleeding, malabsorption, shortness of breath, chest pain, cough, and hemoptysis.
• Diagnosis involves a biopsy of lesions, microscopic examination showing spindle cells, immunohistochemical staining for LANA-1, and PCR for viral DNA.
• Treatment aims to stop the progression of KS.
• Local treatments (radiation therapy, cryosurgery) are used for skin lesions.
• Chemotherapy is used for widespread disease.