The number of cases and severity of disease associated with Dengue infection in Sri Lanka has been increasing since 1989. Studies shows that prior to 2009 DENV2 and DENV3 serotypes are dominant and DENV3 caused the epidemics in the years of 2002 and 2004. In 2009 DENV1 was the major disease causing serotype in Sri Lanka and resulted in 346 deaths. Epidemic in 2012 also caused by DENV1. Why coevolution is critical? Evolution of one species in response to the change in another species or change in environment. In Coevolution of virus and immune system, if humans develop resistance to a virus, the virus could evolve to become resistant to the newly evolved human resistance. In this project we study the process of coevolution of virus and host.