The branch of life science that deals with the frequency and spread of viruses in populations over time is named Epidemiology. It is wont to disrupt the series of infections in populations during outbursts of viral diseases. Host, virus and environmental factors are watched to define the dynamics of viral infections, the ultimate goal is to plan intervention strategies. Programme of viruses is often vertical means from mother to child or horizontal means from person to person. The rate of transmission of viral infections depends on factors that include population density, the number of susceptible individuals, the price of healthcare and therefore the weather·