The epidemiology of virus diseases

This chapter discusses the epidemiology of virus diseases. The epidemiological occurrence of different virus diseases shows marked variations. These concern seasonal and geographical distribution, in addition to the occurrence of diseases in different ages, sexes, and races. The distribution of a disease in a population can also be determined by measurements of immunity to the infectious agent in different age groups, so called seroepidemiology. A prerequisite for such studies is that suitable serological methods are used and that samples are collected from a representative fraction of the population. In the beginning of an acute epidemic, it is particularly important to identify the causative agent. To understand the mechanisms of the spread of infections, three basic circumstances must be taken into consideration, namely, the reservoir and source of infection, the transmission from this source, and the availability of susceptible hosts.