Virus Transmission and Epidemiology

For transmission of a virus to occur, a virus must enter a host through a portal of entry, replicate or disseminate within the host, and be transmitted to a new host through a portal of exit. Unless delivered directly into bodily tissues through a bite or needle, most viruses interact with the epithelium at the site of entry. Localized infections replicate at the initial site of infection, while systemic infections spread to additional areas of the body. Viruses are shed into the environment most often through the same route they entered the body. The stability of virions within the environment is dependent upon virion and environmental factors. Epidemiology is the study of how diseases are transmitted through a population. Epidemiologists perform descriptive or analytic studies to characterize the chain of viral infection throughout a population and design control measures to interrupt it.