How is the varicella-zoster virus (VZV) transmitted?

Varicella-Zoster Virus Transmission

Varicella-zoster virus (VZV) is primarily transmitted through direct contact with skin lesions, airborne droplets, and infected respiratory tract secretions, with an infected person being contagious from 1-2 days before rash onset until all lesions have crusted. 1

Primary Transmission of Varicella (Chickenpox)

• VZV is highly contagious, with 80-90% of susceptible individuals exposed in household settings developing clinical infection 1
• The virus initially enters a susceptible host through the upper respiratory tract or conjunctivae 1, 2
• Transmission occurs via three main routes:
  • Direct contact with fluid from vesicles 2
  • Airborne droplets containing the virus 1
  • Infected respiratory tract secretions 1
• Contagious period extends from 1-2 days before the rash appears until all skin lesions have completely crusted over 1, 2

Transmission Risk Factors

• Secondary cases in household settings are typically more severe than the primary case, likely due to higher viral inoculum from more intense exposure 1
• VZV spreads less readily in tropical climates compared to temperate climates, resulting in higher proportions of serosusceptible adults in tropical countries 1
• Close physical contact with active lesions significantly increases transmission risk 2

Herpes Zoster (Shingles) Transmission

• After primary infection, VZV establishes latency in sensory nerve ganglia and can reactivate years later as herpes zoster 1
• VZV can be transmitted from lesions of patients with herpes zoster to susceptible contacts 1
• The risk of VZV transmission from herpes zoster is approximately 20% of the risk of transmission from primary varicella infection 1
• Important distinction: a person with shingles cannot give another person shingles directly - they can only transmit VZV, which causes chickenpox in susceptible individuals 2

Special Considerations for Contagiousness

• For herpes zoster, contagiousness begins 1-2 days before rash onset and continues until all lesions have dried and crusted, typically 4-7 days after rash appearance 2
• For lesions that do not crust (macules and papules), contagiousness ends when no new lesions appear within a 24-hour period 2
• Immunocompromised patients may experience prolonged viral shedding and extended periods of contagiousness beyond the typical timeframe 2

Vaccine Virus Transmission

• The risk of transmission of varicella vaccine virus from healthy vaccinated persons to susceptible contacts is very low 1
• With over 55 million doses of varicella vaccine distributed since licensure, transmission from immunocompetent persons after vaccination has been documented by PCR analysis from only five persons, resulting in six secondary infections, all mild 1

Clinical Implications

• Healthcare workers with localized herpes zoster should cover all lesions completely and be restricted from caring for high-risk patients until all lesions have dried and crusted 2
• Starting antiviral therapy does not immediately render a patient non-contagious; viral shedding continues until lesions are fully crusted 2
• Immunocompromised patients require special attention due to potential for prolonged viral shedding and higher risk of disseminated infection 2

Understanding VZV transmission mechanisms is crucial for implementing effective prevention strategies and reducing the burden of both primary varicella infection and herpes zoster reactivation.