Читать книгу Basic Virology - Martinez J. Hewlett - Страница 64

The disease caused by infection with smallpox (variola) virus is an example of a much more severe disease than flu, with correspondingly higher mortality rates. There are (or were) two forms of the disease: variola major and variola minor. These differed in severity of symptoms and death rates. Death rates for variola major approached 20%, and during the Middle Ages in Europe, it reached levels of 80% or higher in isolated communities. Virus spread was generally by inhalation of virus aerosols formed by drying exudate from infected individuals. Variola virus is unusually resistant to inactivation by desiccation, and examples of transmission from contaminated material as long as several years after active infection were common.

The disease involves dissemination of virus throughout the host and infection of the skin. Indeed, the pathogenesis of mouse pox described in Chapter 3 provides a fairly accurate model of smallpox pathogenesis. The virus encodes growth factors that were originally derived from cellular genes. These growth factors induce localized proliferation at sites of infection in the skin, which results in development of the characteristic pox (see Chapter 18, Part IV).