Dengue fever is on the rise as world health risks change

Healthy Traveler

AVIAN flu is a worry, of course, if you are headed to Asia. But getting dengue fever is actually a bigger risk on the continent.

In the Caribbean, you're more likely to pick up skin parasites. In sub-Saharan Africa, be wary of ticks, which spread spotted fever.

The health hazards of international travel are changing, according to the results of a study published this month in the New England Journal of Medicine.

"It used to be that malaria was the most common cause of fever in travelers to the tropical countries," says Dr. David O. Freedman, director of the Travelers Health Clinic at the University of Alabama at Birmingham and the lead author of the study.

"Now, except for Africa, where malaria is still the biggest cause of fever, dengue is the most common cause of fever" in returning travelers.

Every year, about 8% of the 50 million people who travel to developing nations get sick enough to seek medical care either during their trip or upon their return. Freedman's team evaluated data on more than 17,000 sick travelers who had returned from trips to countries in six developing regions of the world and had sought care at one of 30 specialized travel or tropical-medicine clinics on six continents belonging to the GeoSentinel network.

GeoSentinel is a data-collection project started in 1995 by the International Society of Travel Medicine and the Centers for Disease Control and Prevention. Its records have given travel medicine specialists a look at the illnesses most likely to infect travelers to the developing world.

The new report confirms what travel medicine doctors have suspected, says Dr. Bradley Connor, past president of the International Society of Travel Medicine. "We already knew dengue was on the rise, but this [report] confirms the fact that dengue is a risk," he says.

Dengue fever usually comes on about four to seven days after a bite from an infected mosquito. Symptoms can include severe headache, joint and muscle pain, high fever, nausea, vomiting and rash.

There's no vaccine or treatment, but travelers should take precautions against being bitten, such as wearing long sleeves and applying repellents with DEET (diethylmetatoluamide). The disease can appear in a more severe form, called dengue hemorrhagic fever, which can be fatal.

But the report also had some surprises, such as the rising incidence of rickettsial infections, usually tick-borne spotted fever, among those returning from sub-Saharan Africa. It occurred more often than typhoid or dengue in sub-Saharan Africa, Freedman says.

"It's an annoying disease but mild," he says. "It's not life-threatening like Rocky Mountain spotted fever. Doxycycline [an antibiotic] cures it quickly. Most doctors prescribe a one-week course to be certain. But in reality a single dose of doxycycline" can cure it.

Symptoms can include fever, headache and malaise. If you are with a knowledgeable guide, Freedman says, he or she will often notice the rash and a characteristic black spot around the tick bite and offer you doxycycline.

Other findings from the report:

Illnesses with fever occurred more among those returning from sub-Saharan Africa or Southwest Asia than from other areas.

Acute diarrhea was higher among those returning from south-central Asia. Regardless of destination, travelers' diarrhea was the most common problem reported, and it was more likely to be parasite-induced than caused by bacteria.

Beyond the report findings, Connor says travelers in 2006 would be wise to be vigilant about avian flu, an infection caused by bird influenza viruses that have surfaced in several Asian nations since 2003.

If you're headed to endemic areas, he says, heed the precautions to stay away from live poultry markets and pass up local delicacies such as raw duck or chicken. Eating thoroughly cooked poultry is OK, he says.

Then there are other health hazards of travel overlooked in the high-profile reports about bird flu and other epidemics, travel medicine experts say. Rabies is one.

"It is prevalent in many parts of the world, including China and India," Connor says. He often recommends travelers who go to those areas get the pre-exposure vaccine, which includes three injections over a month. "If you get the pre-exposure vaccine and you get bitten, you just need two shots three days apart and then you are done. If you don't have the pre-exposure vaccine, you need to get rabies immune globulin, which is difficult to get [in some countries] and expensive — about $500 or $600 — and then you need to get the series, at Day 0, 3, 7, 14 and 28. It changes your entire trip."

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