The souvenir no tourist wants: dengue fever

(Correction: A map from the New England Journal of Medicine in Monday's Health/Science section with a story about dengue fever included Mexico in the shading for Central America. Mexico is in North America.)

A couple of days after Christmas, Rosalie Hornblower was luxuriating in Mexico's warm ocean air south of Acapulco, surrounded by her four adult daughters and a brand-new grandchild. The only thing that disturbed the relaxing scene was a stab from a thirsty mosquito. Hornblower slapped the insect, noting its squirt of blood.

By New Year's Day, Hornblower and three of her daughters had developed high fevers, massive sweats, and severe headaches around the brow line.

Hornblower, already back in the Boston area to report to work as a nurse at Westwood Lodge, made her way to the emergency room. Her daughters, home in other cities, did the same. Their doctors were baffled. One daughter was told she had mononucleosis. Hornblower was put on antibiotics just in case she had a bacterial infection. Malaria was ruled out.

Eventually, more blood work revealed that their platelets were dropping, making the diagnosis clear: They had dengue fever, a virus transmitted by mosquitoes. The only treatment is hydration and pain relief. And the only prevention is to wear insect repellent. Which, though they knew they should, they hadn't.

''We're all pretty much well now," Hornblower said recently. ''I felt good about three days ago" for the first time since becoming ill.

Dengue fever is now the cause of more illness among travelers than malaria everywhere except Africa, according to a recent study in The New England Journal of Medicine.

With international travel for work, vacation, family visits, study, or military action skyrocketing in recent years -- more than 760 million people crossed international borders in 2004 -- doctors' task in quickly diagnosing returning patients has become more and more complex.

And their ability more and more outdated.

Most medical knowledge about travel illnesses has been based on limited data from the 1980s, because the logistics of getting fresh information is difficult and the funding and political will for further study were scant.

The report in the Jan. 12 issue of the New England Journal collected data from 30 clinics on six continents that had seen 17,000 travelers who returned ill from developing nations between 1996 and 2004. It created an up-to-date guide for doctors to link diagnoses with where a person went.

The information is also being used to update the Centers for Disease Control and Prevention website (www.cdc.gov/travel), where travelers can read about health issues in the places where they are going and how to protect themselves.

''This is something we'd like to see basically in every doctor's office," the lead author, Dr. David O. Freedman, director of travel medicine at the University of Alabama at Birmingham, said of the map.

While the report could obviously help doctors who don't see many patients with travel illnesses, it might also benefit with those who do because diseases and country of origin are shifting.

Dr. Julita Mir, an infectious disease specialist who practices internal medicine at the Dorchester House Multi-Service Center, has many patients who visit family in Vietnam, usually to farms or rural areas, where they are vulnerable to everything from avian flu to malaria. Her patients often come in seeking typhoid or polio vaccinations, but malaria pills are expensive and can have nasty side effects, including nightmares.

Dengue, the report found, is an emerging problem in Southeast Asia. Although Mir contracted dengue once herself in her native Venezuela -- ''It's painful like somebody beat you" -- and would recognize the symptoms in someone else, it is not a disease she would normally expect to see in her patients. But now that she's read the study, she said, she's prepared.

Tick fever is also on the rise, particularly in Botswana, according to the study, because more Americans are visiting the country on safaris.

That's why it's so crucial for patients to tell their doctors about their travel history, said Freedman, whose Alabama travel clinic participated in the study.

''It's very easy for me" to diagnose patients with tick fever ''knowing their travel history and taking a 10-second look at the lesion around the tick bite," he said. ''For years, we've been seeing patients who have seen two or three doctors, the symptoms have been going on for days or weeks, and nobody knows what it is."

Indeed, those returning from sub-Saharan Africa were more likely to have tick-borne spotted fever than typhoid or dengue fever, the study showed. And those with diarrhea -- except those who went to Southeast Asia -- were most likely sick from parasites, not bacteria, meaning antibiotics would not help.

Overall, doctors said, prevention is the key to a healthy trip.

It's advice that Hornblower is planning to follow when she returns later this week to her vacation property in Puerto Escondido, a surfer's paradise south of Acapulco.

''I am going to bring repellent down," she said. ''And use it!"

Travel tips

Most common travel illnesses are caused by something you ate or something that bit you. Cover up, wear bug repellent, drink only bottled water, don't use ice cubes, make sure your food is well cooked. Visit a travel clinic before you leave to get malaria pills or antibiotics along with specific advice about health concerns where you are going. Or visit www.cdc.gov/travel for more information.

Dengue:

This mosquito-borne virus is in the same family as West Nile.

Most likely to get it in: Southeast Asia and Central and South America.

Symptoms: High fever, often preceding a rash, searing headache behind the eyes, muscle and joint pain.

Prevention: Wear mosquito repellent with at least 30 percent DEET and reapply every six hours; cover up.

Treatment: Supportive care with fluids and pain medication. Patient can feel washed out for weeks.

Malaria:

Mosquito-borne, possibly life-threatening, parasitic disease.

Most likely to get it in: Africa

Symptoms: High fever, flulike aches.

Prevention: Wear bug repellent, cover up, take antimalaria drugs.

Treatment: The key is to treat before parasite spreads to vital organs.

Diarrhea:

Mostly it's caused by bacteria and resolves itself. But studies show that those who are sick enough to see a doctor often have the parasitic form, which is chronic with a longer incubation period.

Most likely to get it: Parasitic mostly from India, Pakistan, and Nepal; bacterial form is common everywhere, especially Southeast Asia.

Symptoms: Bacterial form is violent, with wrenching cramps for short time; parasitic form is characterized by loose stools and longevity.

Prevention: Drink bottled water and well-cooked food.

Treatments: Travel clinics will prescribe antibiotics to take with you in case of bacterial diarrhea; other drugs for parasites.

TINA CASSIDY

Medical problems by destination

Researchers tracking the medical problems that travelers experienced after visiting developing countries found that illnesses causing fevers were the most common. The figures show the number of cases per 1,000 sick travelers.

	All regions	Caribbean	Central America	South America	Sub-Saharan Africa	South central Asia	Southeast Asia
SYNDROME
Malaria	352	65	133	133	622	139	130
Dengue	104	238	123	138	7	142	315
Typhoid fever	29	22	25	17	7	141	26
Parasitic diarrhea	354	283	403	368	353	453	262
Bacterial diarrhea	268	260	190	253	250	294	369
Intestinal worm	239	278	273	256	307	202	344
Insect bite	187	192	235	156	194	201	179
Allergic rash or reaction	113	148	128	97	105	112	93
Injury	14	23	11	14	7	15	14

The New England Journal of Medicine