Four different dengue viruses are known to cause dengue hemorrhagic fever. Dengue hemorrhagic fever occurs when a person is bitten by a mosquito that is infected with the virus. The mosquito Aedes aegypti is the main species that spreads this disease.
There are more than 100 million new cases of dengue fever every year throughout the world. A small number of these develop into dengue hemorrhagic fever. Most infections in the United States are brought in from other countries. Risk factors for dengue hemorrhagic fever include having antibodies to dengue virus from an earlier infection.