<prompt> Dengue hemorrhagic fever is caused by ?Infection with more virulent dengue virusInfection with same dengue virus repeatedlyInfection with dengue virus in immunocompromized hostInfection with more than one dengue virus  <response>: Ans. is d i.e., Infection with more than one dengue virus DENGUE FEVER Dengue fever is caused by arboviruses at least 4 serotypes have been recognized It is transmitted by Aedes Aedes aegypti is the main vector. The reservoir of infection is both man and mosquito. The transmission cycle is Man-mosquito-man Dengue fever occurs both epidemically and endemically. Epidemics stas in rainy season and are usually explosive. Aedes mosquito becomes infective by feeding on a patient from the day before onset to the 5th day of illness. 