Facts about dengue and yellow fever

Above about dengue and yellow fever.

Dengue is an important human viral disease transmitted by insects. Although nearly half the world's population is at risk for infection and as many as 100 million cases occur annually,¹ we have no antiviral drugs to treat it and no vaccines to prevent it. A closely related but much more lethal mosquito-borne virus, yellow fever, used to be one of the great scourges among humans. Although yellow fever is now largely controlled by vaccination, many regions are susceptible to a reemergence if the disease is introduced by travelers, and substantial recent problems with vaccine safety will no doubt change vaccination policy.

Both dengue and yellow fever are single-stranded RNA viruses in the family Flaviviridae, which includes West Nile virus and approximately 50 others. Substantial progress has been made in understanding the mechanism of the entry of these viruses into cells, the atomic structure of the viral envelope (see figure), the interactions between the molecular determinants and the host antibody, and the mechanism underlying the neutralization of the virus by antibodies.² The unraveling of virus–cell and virus–antibody interactions at the molecular level may lead to the development of antiviral drugs, improved vaccines, and tests for protective and pathological antibodies.

Dengue and yellow fever are endemic to and epidemic in tropical regions (see map). Both are zoonoses maintained in nature by transmission to humans from monkeys or mosquitoes that breed in tree holes. Infected humans have high blood levels of virus and can therefore infect vector mosquitos. After an incubation period of about 10 days, during which the virus replicates in the salivary-gland tissues of blood-feeding aedes mosquitoes, they can transmit the virus to another person. Throughout the tropics, the principal vector for endemic and epidemic spread, Aedes aegypti, has adapted to living among humans in domestic environments. Increasing human population density, urbanization, poor sanitation (creating breeding sites for larval mosquitoes), reinfestation (in the 1970s) of South America by A. aegypti after a successful eradication campaign, and the movement of infected persons by airplanes have contributed to a substantial increase in dengue incidence during the past 50 years.² A. aegypti mosquitoes are prevalent in the southern United States, which is therefore receptive to the introduction and spread of both dengue and yellow fever.