On a recent visit to Cambodia, outside a children’s hospital a block from my hotel, I saw a large red-and-white sign that warned of a severe epidemic of dengue hemorrhagic fever. Years ago, the disease killed our tour guide’s 5-year-old brother.
My tripmates and I managed to escape even the milder form of this mosquito-borne viral infection — we all slept in an air-conditioned hotel and each day applied insect repellent with 30 percent DEET on our exposed skin. But I have since learned that I could have been infected on several previous trips abroad and even in parts of the US.
Dengue (pronounced DEN-gee) fever has increased rapidly in tropicaal and subtropical areas worldwide in recent years, thanks to factors both natural and manmade.
Among the countries that have experienced recent epidemics are Cambodia, Costa Rica, India, Indonesia, Malaysia, the Philippines, Singapore, Thailand and Vietnam. In the Western Hemisphere, outbreaks have also occurred in some Caribbean islands, Cuba, northern Mexico, Nicaragua, Panama, Puerto Rico and Venezuela.
This year, dengue fever has ravaged Rio de Janeiro, infecting more than 75,000 people in Brazil’s Rio state, including Diego Hypolito, a world champion gymnast and gold-medal favorite in the Beijing Olympics this summer. More than 80 people in Rio have died from dengue.
Though most North Americans who receive a diagnosis of dengue fever were infected while traveling to countries where the disease is endemic, including Mexico, it has also struck residents of Hawaii and Texas who had not left US shores. And last summer a related mosquito-borne disease, chikungunya, afflicted more than 100 residents of a village in Italy, Castiglione di Cervia.
The disease is not contagious; rather, it is passed from person to person through the bite of a virus-carrying mosquito.
Epidemiologists say that global warming is allowing the tiger mosquito, Aedes albopictus, a vector of both chikungunya and dengue fever, to survive in areas that were once too cold for it. This mosquito now thrives across southern Europe and even in France and Switzerland. All it takes is one infected traveler to bring the dengue virus home, where the bite of a resident tiger mosquito could transmit it to others.
The primary vector for dengue fever is Aedes aegypti, a daytime biter that is especially active during the early morning and late afternoon. (Unlike the Anopheles mosquito, which transmits malaria, it is not active at night.)
While dengue fever is not as serious a threat as malaria, which afflicts up to 500 million people and kills 1 million each year, both diseases have flourished since DDT, the pesticide that controlled mosquitoes more effectively and inexpensively than any other, fell out of favor in the 1960s. Uncontrolled urbanization and its accompanying population growth, along with inadequate water management systems, have also played a role in the spread of dengue fever.
Dengue fever is caused by any of four variants of a flavivirus, DEN-1, DEN-2, DEN-3 and DEN-4. Other flaviviruses cause West Nile, yellow fever and Japanese encephalitis. While infection by one of the dengue variants confers lifetime immunity to it, a person can still be infected by any of the other three.
The evidence strongly indicates that it is the second infection (though not the third and fourth) that can lead to a far more serious form, dengue hemorrhagic fever, in which the capillaries leak fluid. If not treated soon enough, the hemorrhagic form can result in a life-threatening loss of blood volume and death from dengue shock syndrome.