The varicella-zoster virus (VZV), a herpesvirus belonging to the subfamily of Alphaherpesviridae.
Transmission is via droplets, aerosol or direct contact, or indirectly by touching contaminated items freshly soiled. Patients are usually contagious from a few days before onset of the rash until the rash has crusted over.
Nature of the disease
Varicella is an acute, highly contagious disease. In temperate climates most cases occur before the age of 10 years. The epidemiology is less well understood in tropical areas, where a relatively large proportion of adults in some countries are seronegative. While mostly a mild disorder in childhood, varicella tends to be more severe in adults. It is characterized by an itchy, vesicular rash, usually starting on the scalp and face, initially accompanied by fever and malaise. As the rash gradually spreads to the trunk and extremities, the first vesicles dry out. It normally takes about 7–10 days for all crusts to disappear. The disease may be fatal, especially in neonates and immunocompromised individuals. Complications include VZV-induced pneumonitis or encephalitis and invasive group A- streptococcal infections. Following infection, the virus remains latent in neural ganglia; upon subsequent reactivation, VZV may cause zoster (shingles), a disease affecting mainly immunocompromised individuals and the elderly.
Risk for travellers
Most adult travellers from temperate climates are immune to varicella as a result of natural childhood disease or vaccination whereas nonvaccinated young individuals from low-endemic areas may be at risk of infection when travelling to countries of high varicella endemicity. Immunocompromised individuals are at particular risk of severe disease.