For international travelers, the risk of dengue fever--a viral disease spread by the bite of an infected mosquito--is usually low. But every year, according to the federal Centers for Disease Control and Prevention, cases of dengue, which usually is mild but can be fatal, are confirmed in travelers returning to the United States from visits to endemic areas. In 1996, those areas included most tropical countries in the South Pacific, Asia, the Caribbean, Mexico, Central and South America and Africa.
To reduce the risk of infection, public health experts for years have focused on mosquito abatement programs and educational campaigns for travelers, urging people to cover skin and to use repellents.
But researchers at the University of Michigan and other institutions have made a discovery that eventually could lead to an effective prevention method.
Dr. Rory Marks, an assistant professor of internal medicine at the University of Michigan and his colleagues discovered how the virus attaches itself to cells it will infect. Infection occurs, they found, when the virus binds to a kind of sugar molecule, heparan sulfate, that is found on the surface of cells.
Next, the team used the drug, suramin, to prevent the binding (and thus the infection) from occurring. Suramin's structure mimics the structure of heparan sulfate, so it fools the virus into binding with it instead (and thus, not binding to the cell), said Marks, whose study was published in the August issue of the journal Nature Medicine.
"We looked at three out of four types of dengue fever," said Marks, referring to the four related viruses that can cause the disease. "It was the same mechanism."
Marks does not expect that suramin will be used to prevent human infection. "It gives us clues," he said. Pharmaceutical companies can then develop a drug that would operate in the same manner but be designed specifically to combat dengue.
Gary Clark, an arbovirologist (a dengue virus specialist)and chief of the dengue branch at the Centers for Disease Control and Prevention in San Juan, Puerto Rico, calls the research by Marks' team "interesting and potentially important" but not an immediate solution.
So it's vital, Clark said, that travelers to endemic or epidemic areas educate themselves about the disease. The mosquito responsible for causing dengue fever, the Aedes aegypti, is an urban mosquito. Its larvae favor artificial water containers such as flower pots and vases, discarded tires and buckets.
Day is the most likely time for bites, with two peaks for biting activity: in the morning for several hours after daybreak and in late afternoon for several hours before dark. But the mosquito is capable of biting any time, according to the CDC.
To reduce risk, CDC advises travelers to wear clothing that covers arms and legs and to apply mosquito repellents containing DEET (n, N-diethylmetatoluamide) at concentrations equal to or greater than 30%. Children should avoid concentrations of more than 30%, according to the CDC.
After the bite of an infected mosquito, symptoms can include a high fever that comes on suddenly, a severe frontal headache and joint and muscle pain. There also can be nausea, vomiting and a rash. The rash often appears three to five days after the fever. It may spread from the torso to the arms, legs and face.
Usually the disease, for which there is no specific treatment or vaccine, is benign. However, recovery--with rest and medicine for symptom relief--can take some time. The more severe form, dengue hemorrhagic fever, is rarer but can be fatal.
Last year, 250,707 cases of dengue fever were reported in the Americas, according to Jose Rigau, medical epidemiologist at the CDC dengue branch, citing statistics from the Pan American Health Organization. Of those, 4,440 were dengue hemorrhagic fever. In all, 47 deaths were reported.
In dengue hemorrhagic fever, blood vessel damage occurs. Symptoms can include internal bleeding, circulatory failure, shock and coma. It most often affects children.
Symptoms may not appear until after travelers return home. Travelers who experience a sudden onset of fever within a month after returning from a dengue endemic or epidemic area should consult their physician, according to the CDC.
The Healthy Traveler appears the second and fourth week of every month.