Dengue, a mosquito-borne viral disease, threatens about 2.5 billion people -- more than 40 percent of the world's population -- a U.N. report said. The U.N.'s World Health Organization said in its latest report the disease -- which in its severest form is a leading cause of serious illness and death among children in some Asian and Latin American countries -- is endemic in more than 100 countries. The disease was endemic only in nine countries in the 1970s. "The incidence of dengue has grown dramatically around the world in recent decades," the report said. The agency said it estimates there may be 50 million to 100 million dengue infections worldwide every year. The infection, which causes flu-like illness and occasionally develops into a potentially lethal complication called severe dengue, is transmitted to humans by infected female vector mosquitoes. After virus incubation for as much as 10 days, an infected mosquito is capable of transmitting the virus for the rest of its life. There is no specific treatment for dengue or severe dengue, but early detection and access to proper medical care lowers fatality rates below 1 percent. The only way to prevent the transmission of the dengue virus is to control mosquitoes that carry the disease. "Not only is the number of cases increasing as the disease spreads to new areas, but explosive outbreaks are occurring," the report said, adding the threat of a possible outbreak of dengue fever exists in Europe.