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Microbiology

Vesicles & Lesions

This section covers viruses that cause vesicles and lesions, focusing on Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV). We’ll cover their etiology, epidemiology, transmission, and the specific disease states they cause

Etiology, Epidemiology, Transmission, and Disease States

Herpes Simplex Virus (HSV)

  • Etiology
    • Classification: A member of the Herpesviridae family
    • Types
      • HSV-1: Typically associated with oral herpes (cold sores) but can also cause genital herpes
      • HSV-2: Typically associated with genital herpes but can also cause oral herpes
  • Epidemiology
    • Global Distribution: HSV is found worldwide
    • Prevalence: Very common, with a high percentage of the population infected with HSV-1 and a significant proportion infected with HSV-2
    • Age Groups
      • HSV-1: Often acquired in childhood through non-sexual contact
      • HSV-2: Typically acquired through sexual contact
  • Transmission
    • Direct Contact: Spread through direct contact with an active lesion or through asymptomatic shedding (virus being present without visible symptoms)
    • Sexual Contact: HSV-2 is primarily transmitted through sexual contact
    • Mother to Child: Can be transmitted from mother to child during childbirth (neonatal herpes)
  • Disease States
    • Oral Herpes (Cold Sores): Characterized by painful blisters on or around the lips
    • Genital Herpes: Characterized by painful blisters on the genitals, buttocks, or inner thighs
    • Herpetic Whitlow: Infection of the fingers or around the fingernails
    • Herpes Keratitis: Infection of the cornea of the eye, which can lead to blindness
    • Herpes Encephalitis: A rare but serious infection of the brain
    • Neonatal Herpes: Can cause severe illness in newborns, including skin, eye, and mouth infections, encephalitis, and disseminated disease
    • High-Risk Groups: Immunocompromised individuals are at higher risk for severe HSV infections

Varicella-Zoster Virus (VZV)

  • Etiology
    • Classification: A member of the Herpesviridae family
    • Relationship: Causes two distinct diseases: varicella (chickenpox) and herpes zoster (shingles)
  • Epidemiology
    • Global Distribution: VZV is found worldwide
    • Chickenpox: Historically, a common childhood disease, but incidence has decreased significantly with the introduction of the varicella vaccine
    • Shingles: Occurs in individuals who have previously had chickenpox. The virus remains dormant in nerve cells and can reactivate later in life
    • Age Groups
      • Chickenpox: Primarily affects children
      • Shingles: More common in older adults and immunocompromised individuals
  • Transmission
    • Chickenpox
      • Airborne Droplets: Spread through airborne droplets produced when infected individuals cough or sneeze
      • Direct Contact: Can also be transmitted through direct contact with lesions
    • Shingles
      • Direct Contact: Spread through direct contact with lesions. Shingles is not spread through the air
      • Risk to Others: Individuals with shingles can transmit VZV to people who have never had chickenpox or been vaccinated, causing them to develop chickenpox
  • Disease States
    • Varicella (Chickenpox): Characterized by a widespread, itchy rash with small, fluid-filled blisters
      • Complications: Secondary bacterial infections of the skin, pneumonia, encephalitis, and, rarely, death
    • Herpes Zoster (Shingles): Characterized by a painful rash with blisters that typically occurs in a single stripe on one side of the body
      • Postherpetic Neuralgia (PHN): Chronic pain that can persist for months or years after the shingles rash has resolved
      • Ophthalmic Zoster: Shingles involving the eye, which can lead to vision loss
      • Disseminated Zoster: Widespread rash involving multiple dermatomes, more common in immunocompromised individuals
    • High-Risk Groups
      • Chickenpox: Unvaccinated individuals, pregnant women, and immunocompromised individuals are at higher risk for severe disease
      • Shingles: Older adults and immunocompromised individuals are at higher risk for shingles and complications

Important Notes

  • Prevention
    • Varicella Vaccine: Highly effective in preventing chickenpox
    • Zoster Vaccine: Available to prevent shingles and its complications
  • Diagnosis
    • HSV/VZV: Diagnosed through viral culture, PCR, or direct fluorescent antibody (DFA) testing of lesion specimens
  • Treatment
    • Antiviral Medications: Acyclovir, valacyclovir, and famciclovir are used to treat HSV and VZV infections

Key Terms

  • Etiology: The cause or origin of a disease or condition
  • Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems
  • Transmission: The way a disease is spread from one person or source to another
  • Vesicle: A small, fluid-filled blister
  • Lesion: An area of damaged tissue or skin
  • Asymptomatic Shedding: The presence and shedding of a virus without visible symptoms
  • Neonatal Herpes: HSV infection in newborns
  • Herpetic Whitlow: HSV infection of the fingers or around the fingernails
  • Herpes Keratitis: HSV infection of the cornea of the eye
  • Herpes Encephalitis: HSV infection of the brain
  • Varicella: Chickenpox
  • Herpes Zoster: Shingles
  • Postherpetic Neuralgia (PHN): Chronic pain that persists after the shingles rash has resolved
  • Ophthalmic Zoster: Shingles involving the eye
  • Disseminated Zoster: Widespread shingles rash involving multiple dermatomes
  • Dermatome: An area of skin supplied by a single spinal nerve