DefinitionDengue hemorrhagic fever is a severe, potentially deadly infection spread by certain species of mosquitoes (Aedes aegypti).See also: Dengue feverAlternative NamesHemorrhagic dengue; Dengue shock syndrome; Philippine hemorrhagic fever; Thai hemorrhagic fever; Singapore hemorrhagic feverCauses, incidence, and risk factorsFour different dengue viruses are known to cause dengue hemorrhagic fever. Dengue hemorrhagic fever occurs when a person catches a different type dengue virus after being infected by another one sometime before. Prior immunity to a different dengue virus type plays an important role in this severe disease.Worldwide, more than 100 million cases of dengue fever occur every year. A small number of these develop into dengue hemorrhagic fever. Most infections in the Uni