Dengue (pronounced DEN-ghee) fever is a tropical disease spread by mosquitoes. It is caused by any one of four closely related dengue viruses -- DENV 1, DENV 2, DENV 3 or DENV 4 -- carried most often by the Aedes aegypti mosquito, and less frequently, by Aedes albopictus.
The most common vector-borne viral disease in the world, it causes an estimated 50-100 million infections and 25,000 deaths each year.
Generally most prevalent in tropical and subtropical areas, dengue made a return to Key West, Fla., in 2009 after being absent since 1934.
There were 27 known cases there last year and 18 so far this year. Some carriers never feel ill, but many sufferers report excruciating bone pain, leading some to call dengue "break-bone fever." Complications can be fatal.
Why is dengue fever an issue now in the United States?
No one can say for sure why it turned up South Florida, but a May report from the U.S. Centers for Disease Control and Prevention in Atlanta suggests some possibilities:
Dengue might have been present in the community earlier, but is only being detected now.
The conditions for dengue transmission long have been present in South Florida. Epidemiologists say dengue could have reappeared in Florida when an infected international visitor passed the virus to local mosquitoes, or a mosquito carrying dengue hopped a ride on a cruise ship or airplane. Key West has lots of Aedes aegypti, a mosquito that is the most effective dengue carrier.
The large numbers of domestic visitors also might increase the risk for spread in other parts of the United States.
It's misleading to think there's been no dengue fever in the United States until now. In fact, in the last five years, there have been dengue outbreaks in both Florida and Texas, according to the American Society of Tropical Medicine and Hygiene.
The disease disappeared from 1946-1980, when there were no reported cases acquired in the continental United States. Then, beginning in the 1980s, dengue fever re-emerged as a widespread tropical infection throughout Central America and the Caribbean, especially in Cuba, the Dominican Republic and Puerto Rico.
Since 1980, there have been seven localized outbreaks along the Texas-Mexico border, including one in the small border town of Brownsville, Texas, in 2005.
Where do health officials expect dengue to hit next?
The American Society of Tropical Medicine and Hygiene says that based on recent outbreaks, dengue could become a health threat in major Gulf Coast cities such as Corpus Christi, Texas; Houston; New Orleans; Biloxi, Miss.; Mobile, Ala.; Pensacola, Fla., and Tampa, Fla., as well as in less populated areas.
Right now, CDC officials are keeping a close eye on Puerto Rico, where suspected dengue cases are being recorded at a level unseen since a major epidemic in 1998. There are major similarities between worldwide climate patterns in 2009-10 and those in 1997-98, when there also was a strong El Nino climate phenomenon that brought warmer weather to Puerto Rico. Dengue viruses reproduce more rapidly in warm weather, according to Robert S. Hope of Yale University.
What are the signs and symptoms of dengue?
The incubation period for dengue fever is typically 4 to 7 days, but can be 3 to 14 days. The main symptoms are a high fever and at least two of the following:
Severe pain behind the eyes