The sixth chapter on the disease epidemiology reports the interactions among different variables of host, environment and pathogen and the resultant effects on temporal progression of the disease. The disease cycles that have been proposed at different times by linking different developmental stages of the malformation symptoms have been depicted in this chapter. The patterns of the epidemic both temporally and spatially have been traced. Different types of mathematical modeling to quantity the changes in disease level with passage of time were proposed. Prediction equations based on weather, host and pathogen variables were worked out by various workers. Recently an Expert System to predict the disease incidence in any state of India and to suggest appropriate IPM strategies has been developed. This has been made available in a CD with this monograph.