At the end of the 19th century, varicella was reliably distinguished from the smallpox virus. In 1888, von Bokay demonstrated the relationship between varicella and herpes zoster when he exposed susceptable children to patients with zoster. Thomas Weller in 1954 isolated the varicella zoster virus from the vesicular lesions of both chicken pox and zoster. The varicella virus enters the body via the conjunctivae and the respiratory tract. It requires host to host tramsmission because of it's short survival time outside of the body.
Replication is believed to occur at the site of entry and in regional lymph nodes.
It's primary viremia occurs after approximately 4-6 days, during which the virus disseminates to the sensory ganglia, liver, spleen and other organs. Following further replication in these organs, a secondary viremia develops during which the skin is infected. The virus can be isolated from the mononuclear cells of an infected person approximately 5 days prior to and up to 1 to 2 days following the appearance of the rash. The average incubation period for the varicella virus is 14-16 days. In immunocompromised patients this period can be prolonged and can last up to 28 days following the administration of varicella zoster immune globulin.