Varicella zoster virus is a highly infective pathogen distributed worldwide.
Chickenpox is exclusively a human disease. No animal reser-voirs are present. A chickenpox or herpes zoster patient is the source of infection. Varicella zoster virus is shed mainly in the respiratory secretions and also in the vesicular lesions of the skin. The infectivity is maximum during the early stage of the disease when the virus is shed in large numbers in respiratory secretions. The buccal lesions and vesicular fluid, which are rich in virus content, are highly infectious and are sources of infec-tion. Scabs do not contain any viruses, hence are noninfectious.
Chickenpox is transmitted primarily by inhalation of respiratory secretions. The infection may also occur by direct contact with vesicular lesions on the skin. Herpes zoster is a reactivation of latent varicella zoster virus infection, hence is not acquired from an infected patient.
Chickenpox is mainly a disease of children. In herpes zos-ter infection, people of all ages are affected. The incidence of the disease, however, increases with age, due to the decrease in immune functions that occurs during aging.