Description

Dengue fever, with the risk of capillary leakage, bleeding, and death from dengue hemorrhagic fever (DHF), is a viral disease transmitted by Aedes mosquitoes, usually Ae aegypti. The four dengue viruses are immunologically related but do not provide cross-protective immunity. In fact, infection with subsequent immunity to one serotype of Dengue virus increases the risk of developing DHF upon later infection with another serotype.

History of Dengue

The first reported epidemics of dengue fever occurred in 1779-1780 in Asia, Africa, and North America; the near simultaneous occurrence of outbreaks on three continents indicates that these viruses and their mosquito vector have had a worldwide distribution in the tropics for more than 200 years. During most of this time, dengue fever was considered a benign, nonfatal disease of visitors to the tropics. Generally, there were long intervals (10-40 years) between major epidemics, mainly because the viruses and their mosquito vector could only be transported between population centers by sailing vessels.

Perspectives

Dengue and DHF are caused by one of four closely related but antigenically distinct virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4), of the genus Flavivirus. Infection with one of these serotypes does not provide cross-protective immunity, so persons living in a dengue-endemic area can have four dengue infections during their lifetime. Dengue is primarily a disease of the tropics, and the viruses that cause it are maintained in a cycle that involves humans and Aedes aegypti, a domestic, day-biting mosquito that prefers to feed on humans. Infection with dengue viruses produces a spectrum of clinical illness ranging from a nonspecific viral syndrome to severe and fatal hemorrhagic disease. Important risk factors for DHF include the strain and serotype of the infecting virus, as well as the age, immune status, and genetic predisposition of the patient.

Occurrence

Dengue, a rapidly expanding disease in most tropical and subtropical areas of the world, has become the most important arboviral disease of humans. More than 2.5 billion persons now live in areas at risk of infection, and an estimated 50 to 120 million cases of dengue fever occur each year, 500,000 of which are DHF. The fatality rate for DHF averages 5%. Epidemics caused by all four virus serotypes have become progressively more frequent and larger in the past 20 years. As of 2002, dengue fever is endemic in most tropical countries of the South Pacific, Asia, the Caribbean, the Americas, and Africa (see Map). Additionally, most tropical urban centers in these regions have multiple dengue virus serotypes co-circulating (hyperendemicity), which increases dengue transmission and the risk of DHF. Future dengue incidence in specific locales cannot be predicted accurately, but a high level of dengue transmission is anticipated in all tropical areas of the world for the indefinite future. The incidence of the severe disease, DHF, has increased dramatically in Southeast Asia, the South Pacific, and the American tropics in the past 20 years, with major epidemics occurring in many countries every 3­5 years. DHF is an emerging disease in the Americas. The first major epidemic occurred in Cuba in 1981, and a second major epidemic of DHF occurred in Venezuela in 1989 and 1990. Since then, outbreaks or sporadic cases, or both, of confirmed DHF have occurred in 28 tropical American countries. After an absence of 35 years, a small number of autochthonous cases of dengue fever have been documented in the continental United States (southern Texas in 1980, 1986, and 1995). This outbreak was associated with imported cases and epidemic dengue in adjacent states in Mexico. After an absence of 56 years, a limited outbreak of dengue fever occurred in Hawaii in 2001, associated with imported cases and epidemic dengue in the South Pacific.