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Chickenpox/Shingles

Epidemiology of Infectious Diseases: Chickenpox/Shingles

Causal agent
A systemic viral infection caused by infection with human varicella-zoster virus (VZV), a member of the herpesvirus family1.

Herpes Zoster (shingles) is caused by reactivation of latent varicella infection whose genomes persist in sensory root ganglia of the brain stem and spinal cord2.

Common clinical features

  • Generally a mild disease in children lasting 4-7 days, sometimes characterized by a short prodromal period (low-grade fever, malaise) and followed by a vesicular rash (usually on the trunk) lasting 3-4 days which become granular scabs. There are successive crops of vesicles over several days.
  • The most common complications from varicella infection are bacterial infections of the skin and soft tissues in children and pneumonia in adults.
  • Severe complications include, septicaemia, toxic shock syndrome, necrotizing fiscilitis, osteomyelitis, bacterial pneumonia and septic arthritis.
  • Congenital varicella syndrome occurs following infection during pregnancy (first 5 months), although most risk appears to be in weeks 13-202.
  • Herpes zoster (shingles) is more prevalent among older age groups.

Epidemiology

  • Endemic worldwide, occurring mainly in children. The incidence in older children and adults is rising in the UK and other Western countries2.
  • In temperate climates, 90% of individuals have been infected by age 15 and 95% by young adulthood. In tropical climates a higher proportion of cases occur in adults.

Reservoir
Humans.

Mode of transmission
Direct person to person contact, by droplet or airborne spread of vesicular fluid or respiratory secretions. Also by contact with articles recently contaminated by discharges from vesicles and mucous membranes from an infected person1,2.

Highly contagious infecting up to 90% of those exposed.

Incubation period
2-3 weeks, commonly 14-16 days. Longer following passive immunization or in the immunodeficient.

Period of Communicability
Commonly 1-2 days following onset of rash and until all lesions are crusted (usually 5 days).

Prevention and control
Exclude children with chickenpox from school until 5 days from the onset of rash. Infected healthcare workers should be excluded from work for the same period2.

References

  1. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
  2. Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.

© CM Kirwan 2006