Dengue Causes and Risks: There are four Dengue viruses (DENV-1 to 4) that causes Dengue fever, all of which are spread by a species of mosquito known as the Aedes aegypti mosquito. The virus is transmitted from an infected mosquito to human. The process begins when a person who is infected with the Dengue virus is bitten by a mosquito; the virus is then passed on when someone else is then bitten by the infected mosquito. One type of dengue virus can infect you only once. The high risk areas for catching dengue fever are urban areas where the population density is high and sanitation is poor and in rural areas. Dengue fever can occur if the environment is friendly for mosquito breeding which means stagnant water which is their breeding ground. For more information about dengue risk factors and it causes, read the listed articles.