Herpes simplex virus

• Comprises herpes simplex virus 1 (HSV-1) and HSV-2, which are members of the Human herpesvirus family
• Cause typical painful vesicular lesions on labia or external genitals
• Occasionally cause a viral encephalitis

Background

Microbiology

• Enveloped, double-stranded DNA virus
• HSV-1 and HSV-2 are morphologically and genetically distinct viruses
• Can be infected with both

Epidemiology

• Worldwide distribution, and only found in humans
• Most common cause of genital lesions
• Spread through person-to-person contact with skin or mucosa; not spread via fomits
• HSV-1 is more common, with 90% of adults having antibodies by age 40
  • Often acquired in childhood in Asia and Africa
  • More common in lower SES populations
• HSV-2 has seroprevalence of 15-20% in US
  • More common in women than men, in HIV-infected people, and in MSM
  • May be subclinical if already infected with HSV-1

Pathophysiology

• Fusion of envelope and cell membrane is mediated by viral glycoproteins B, C, and D and host cell proteins cellular heparin sulfate, TNF receptors, and immunoglobulins
• Internal capsid is released, which makes its way to the nucleus
• Viral DNA polymerase enzyme and viral DNA helicase are targets of antivirals
• Viral DNA may remain latent in about 10% of nearby neurons, characterized by latency-associated transcripts (LATs)
  • Despite being latent, virus can still be shed in mucosa anywhere from 1/10 to 3/4 of days
• HSV-1 prefers trigeminal ganglia as well as cervical ganglia, or sacral nerve root ganglia if genital

Clinical Presentation

• Incubation period usually within 5 days for primary infection