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Clinical Features
Aedes aegypti are most active during the day. These vector mosquitoes are found near human habitations and are often present indoors. Epidemic transmission is usually seasonal, during and shortly after the rainy season. Dengue fever is characterized by sudden onset, high fever, severe headaches, joint and muscle pain, nausea/vomiting, and rash. The rash may appear 3–4 days after the onset of fever. Infection is diagnosed by a blood test that detects the presence of the virus or antibodies. The illness may last up to 10 days, but complete recovery can take 2–4 weeks. Dengue is commonly confused with other infectious illnesses such as influenza, measles, malaria, typhoid, leptospirosis, and scarlet fever. The symptoms of dengue can be treated with bed rest, fluids, and medications to reduce fever, such as acetaminophen; aspirin should be avoided. Travelers should alert their physician of any fever illnesses occurring within 3 weeks after leaving an endemic area. There is no vaccine for dengue fever; therefore, the traveler should avoid mosquito bites by remaining in well screened or air-conditioned areas. Travelers to tropical areas are advised to use mosquito repellents on skin and clothing, to bring aerosol insecticides to use indoors, and use bednets. Risk Groups The risk of dengue for each geographic area will have variations. The risk is generally higher in urban areas. There are no requirements precluding traveler entry to any country.
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. A global pandemic of dengue began in Southeast Asia after World War II and has intensified during the last 15 years. Epidemics caused by multiple serotypes (hyperendemicity) are more frequent, the geographic distribution of dengue viruses and their mosquito vectors has expanded, and DHF has emerged in the Pacific region and the Americas. In Southeast Asia, epidemic DHF first appeared in the 1950s, but by 1975 it had become a leading cause of hospitalization and death among children in many countries in that region. Trends
The emergence of dengue/DHF as a major public health problem has been most dramatic in the American region. In an effort to prevent urban yellow fever, which is also transmitted by Ae. aegypti, the Pan American Health Organization organized a campaign that eradicated Ae. aegypti from most Central and South American countries in the 1950s and 1960s. As a result, epidemic dengue occurred only sporadically in some Caribbean islands during this period. The Ae. aegypti eradication program, which was officially discontinued in the United States in 1970, gradually eroded elsewhere, and this species began to reinfest countries from which it had been eradicated. In 1997, the geographic distribution of Ae. aegypti was wider than its distribution before the eradication program. By 1997, 18 countries in the American region had reported confirmed DHF cases, and DHF is now endemic in many of these countries. In 1997, dengue is the most important mosquito-borne viral disease affecting humans; its global distribution is comparable to that of malaria, and an estimated 2.5 billion people live in areas at risk for epidemic transmission. Each year, tens of millions of cases of dengue fever occur and, depending on the year, up to hundreds of thousands of cases of DHF. The case-fatality rate of DHF in most countries is about 5%; most fatal cases are among children and young adults. World Distribution of Dengue - 2000
There is a small, but significant, risk for dengue outbreaks in the continental United States. Two competent mosquito vectors, Ae. aegypti and Aedes albopictus, are present and, under certain circumstances, each could transmit dengue viruses. Moreover, numerous viruses are introduced annually by travelers returning from tropical areas where dengue viruses are endemic. Many cases probably go unreported each year because surveillance in the United States is passive and relies on physicians to recognize the disease, inquire about the patient's travel history, obtain proper diagnostic samples, and report the case. These data suggest that southern Texas and the southeastern United States, where Ae. aegypti is found, are at risk for dengue transmission and sporadic outbreaks. Challenges
The reasons for this dramatic global emergence of dengue/DHF as a major public health problem are complex and not well understood. However, several important factors can be identified. First, effective mosquito control is virtually nonexistent in most dengue-endemic countries. Second, major global demographic changes have occurred, the most important of which have been uncontrolled urbanization and concurrent population growth. These demographic changes have resulted in substandard housing and inadequate water, sewer, and waste management systems, all of which increase Ae. aegypti population densities and facilitate transmission of Ae. aegypti-borne disease. Third, increased travel by airplane provides the ideal mechanism for transporting dengue viruses between population centers of the tropics, resulting in a constant exchange of dengue viruses and other pathogens. Lastly, in most countries the public health infrastructure has deteriorated. Limited financial and human resources and competing priorities have resulted in a "crisis mentality" with emphasis on implementing so-called emergency control methods in response to epidemics rather than on developing programs to prevent epidemic transmission. This approach has been particularly detrimental to dengue control because, in most countries, surveillance is (just as in the U.S.) very inadequate; the system to detect increased transmission normally relies on reports by local physicians who often do not consider dengue in their differential diagnoses. As a result, an epidemic has often reached or passed transmission before it is detected. Future Outlook No dengue vaccine is available. Recently, however, attenuated candidate vaccine viruses have been developed in Thailand. These vaccines are safe and immunogenic when given in various formulations, including a quadrivalent vaccine for all four dengue virus serotypes. Efficacy trials in human volunteers have yet to be initiated. Research is also being conducted to develop second-generation recombinant vaccine viruses; the Thailand attenuated viruses are used as a template. Therefore, an effective dengue vaccine for public use will not be available for 5 to 10 years. Prospects for reversing the recent trend of increased epidemic activity and geographic expansion of dengue are not promising. New dengue virus strains and serotypes will likely continue to be introduced into many areas where the population densities of Ae. aegypti are at high levels. With no new mosquito control technology available, in recent years public health authorities have emphasized disease prevention and mosquito control through community efforts to reduce larval breeding sources. Although this approach will probably be effective in the long run, it is unlikely to impact disease transmission in the near future. We must, therefore, develop improved, proactive, laboratory-based surveillance systems that can provide early warning of an impending dengue epidemic. At the very least, surveillance results can alert the public to take action and physicians to diagnose and properly treat dengue/DHF cases.
Source: CDC Dengue Fever Pages
For further information, see Dengue: Just the Facts from USACHPPM.
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| Sponsored by the Army National Guard, and the Office of the Chief, Army Reserve. Copyright 2008 |
Dengue and dengue hemorrhagic fever (DHF) are caused by one of four closely related serotypes of the genus Flavivirus. 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.
