As tourism widens its net, the mosquitoes trapped inside may prove lethal. Alan Burdick assesses today's risks

Only a few days before returning home from Kenya, a 23-year-old British woman—let's call her Mary—started feeling dizzy. By the next day she was struggling with what felt like a hangover but wasn't; sensing trouble, she visited a hospital. Mary's instincts were sound: she had been felled by malaria. Unfortunately, her diagnosis came too late. Early the third morning, she dropped into a coma and died.

Most travelers think of malaria as yesterday's disease, the plague of pith-helmeted explorers hacking their way through the Congo. In fact, there are 300 to 500 million cases of malaria each year. Of these, 1.5 to 2.7 million result in death. The majority of malaria victims are poverty-stricken, often children, with no access to the modern arsenal of antimalarial drugs. But with international travel increasing by roughly 7 percent annually, a growing number of Western travelers are exposed to the disease.

Each year, 1,200 to 1,500 American travelers are hospitalized with malaria upon returning home. Overall, as many as 30,000 North American and European travelers are afflicted annually, though Western travelers rarely die of the disease. (Mary was unlucky: she acquired the one strain that can be fatal to humans; the others are merely severely debilitating.) Yet, as a species, we are peculiarly susceptible to hubris. One survey found that half the travelers passing through the Nairobi airport were not taking their antimalarial drugs as directed. (Mary's doctors aren't certain, but she may have fit into this category.) Increasingly, however, even the wise traveler is at risk. Epidemiologists note with alarm that malaria is becoming resistant to all known drugs, precisely at a time when Third World destinations have grown popular.

For centuries, the illness was thought to be caused by the dank effervescences of swamps; hence its name: mal aria, "bad air." In fact, malaria is caused by a parasite, a microscopic protozoan of the genus Plasmodium, which is transmitted by mosquitoes—in particular, mosquitoes of the genus Anopheles. Although Anopheles mosquitoes are found throughout the world, malaria is restricted primarily to the tropics. Ninety percent of cases occur in sub-Saharan Africa, and two-thirds of the remaining 10 percent in six countries: India, Brazil, Sri Lanka, Vietnam, Colombia, and the Solomon Islands. In recent years malaria has also crept into the southern republics of the former Soviet Union. Once confined to rural areas, it now threatens the urban centers of the tropics: Nairobi, Abidjan, Dakar, Calcutta, Delhi.

Although some epidemiologists argue that global warming could push malaria, prevalent in the southeastern United States in the 18th century, back into this country, most agree that, unless we revert to living in lean-tos amid pools of stagnant water, we'll be fine. Nonetheless, some Western nations have had a few strange encounters with the disease. Last year Australia reported its first case of "airport malaria": a Queensland man contracted the disease after being bitten by a mosquito that had apparently hitchhiked onto an international flight. Similar cases have cropped up around major airports in Spain, England, France, and Switzerland, where the Geneva-based World Health Organization draws a steady flow of workers and visitors from malaria-plagued countries. One doctor even described an incident of so-called stopover malaria, wherein a handful of travelers were taken sick after their plane refueled in West Africa.

Such cases are extremely rare—which is just as well, since there isn't much you can do to prevent them. Regular "traveler's malaria," however, demands your full attention.

Of the many strains of the malaria parasite, four infect humans. Plasmodium vivax, which can lie dormant in your liver for several years, is found throughout the world; untreated, it can inflict recurrent, incapacitating fatigue. The deadly variety, Plasmodium falciparum, can kill within 24 hours of the onset of symptoms. All four strains work in more or less the same way. Once in the bloodstream, the parasite heads for the liver and sets up shop. After approximately two weeks, it re-enters the bloodstream and begins infecting red blood cells, popping them, slurping up the hemoglobin, and clogging brain capillaries, multiplying rapidly as it starves your body of oxygen.

Only at this point do outward symptoms appear: fatigue, anemia, dizziness, fever or chills, nausea. In short, malaria feels like jet lag, flu, or food poisoning, its symptoms easily ascribed to any number of ailments that strike the average traveler. That is precisely what makes it so insidious. American doctors often don't think to diagnose it. Though African doctors do (the slogan there is "Fever equals malaria, unless proven otherwise"), they may not have the medication to treat it. Still, the message is clear. "If you don't feel quite right, take it seriously," says Mary Galinski, founder and president of Malaria Foundation International. "Mention malaria to your doctor, and don't be afraid to be persistent."

the antimalarial drug of choice used to be a pleasant little prophylaxis called chloroquine. What the birth control pill was to sex, chloroquine was to malaria: armed with chloroquine pills, the intrepid traveler could visit the soggiest, most mosquito-ridden corner of the earth fully secured against the ravages of malaria. But the days of chloroquine's supremacy are over. Except for select areas in Central America, the Caribbean, North Africa, and the Middle East where the drug is still effective, chloroquine is no longer the panacea it once was; malaria has evolved resistance to it. A new generation of antimalarial drugs has risen in chloroquine's wake, with varying degrees of effectiveness in different countries, depending on which strain of malaria prevails. Of these drugs, the best and most widely prescribed is mefloquine. Better known by its brand name, Lariam, mefloquine prevents malaria in most parts of the world, and is deemed upward of 97 percent effective.

The problem with mefloquine is its side effects, or at least the rumor of them—everything from mild nausea and dizziness to hallucinatory dreams and full-blown psychoses. Lately, Britain has experienced something of a Lariam scare, fueled by sensational news reports of suspect validity. (In a moment worthy of the Twinkie Defense, a school principal blamed Lariam for his embezzlement of educational funds.) The result has been unfortunate: the number of malaria cases among British travelers has risen fivefold in the past year alone, largely because people have been scared off the best antimalarial drug.

But according to Dr. Hans Lobel, a malaria researcher at the Centers for Disease Control in Atlanta, there is little solid evidence that mefloquine actually causes widespread psychotic reactions. Described by one researcher as "the world expert on mefloquine psychoses," Lobel has performed or pored over dozens of studies and surveys of the side effects of mefloquine and its antimalarial kin. One problem he found is that many alleged side effects—insomnia, indigestion, nausea—are symptoms that might be experienced for much more mundane reasons. On the whole, he found, mefloquine is "as well tolerated as chloroquine." The incidence of severe psychological reactions to mefloquine is about one in 13,000—which, Lobel notes, is one-sixteenth the incidence in the general population. "That's no proof that it doesn't happen," Lobel says, "but it does make it less likely." (My own parents, who took mefloquine during a recent trip to India, expressed surprise when I asked about side effects—they hadn't experienced any, nor had anyone else in their tour group.)

In a few years it may not matter which antimalarial drug you take. Malaria is becoming resistant to all of them. Already in northern Thailand, along the border with Burma, mefloquine no longer works. And the only prophylactic still effective there, doxycycline, doesn't work as it once did. "There are no curative drugs [for that strain of malaria] that are suitable at all," says Dr. Amir Attaran, founder of the Malaria Project, a lobbying group. "If you're in northern Thailand, even if you've done all the right things, taken the right drug, and you get the disease, your only hope is to pray." Some researchers fear that within a decade, Plasmodium falciparum, the lethal strain of malaria, could develop multiple-drug resistance.

To make matters worse, there are few new antimalarial drugs on the horizon. According to a 1996 report by the National Academy of Sciences, not a single Western pharmaceutical company is developing one. With federal and international financing of malaria research hovering at a pitiful level, says Attaran, "it doesn't take a rocket scientist to see where we'll be in ten years."

Alan Burdick, a former science editor at the New York Times Magazine, is at work on a book about invasive species to be published by Farrar, Straus & Giroux next fall.

Preventive Measures
First: "Absolutely, positively see your doctor before a trip to the tropics," says Dr. Amir Attaran, founder of the Malaria Project. (If you're unsure whether you are at risk of contracting malaria where you're going, check the Web site of the Centers for Disease Control: It lists health risks for destinations around the world and provides updated information on which antimalarial drug is recommended for which destination.) Show your doctor a copy of your itinerary. Every antimalarial drug has a varying degree of efficacy in different parts of the world. Depending on your travel plans, you might need to pack as many as three different drugs.

Second: "Take the drugs!" says Attaran. "The number of people who think a drug has magical properties if it's carried in a suitcase is unbelievable. It's not a talisman. You can't hang it around your neck like garlic. Take it, and take it regularly. It's your only defense." Most malaria prophylactics must be ingested for at least four weeks after returning from your trip; don't forget to do so.

Third: Avoid mosquitoes. (Sure, like you hope to attract them.) Wear long sleeves and trousers, particularly during evening hours when the bugs are most active. Pack a mosquito net and sleep under it. Burn insect coils at night. If given a choice, take the hotel room with window screens. And wear repellent. Brands containing deet are particularly effective; a 30-percent concentration will suffice. (I once spilled some full-strength deet on my Swiss Army knife and melted the plastic.) Citronella, sometimes favored as a "natural" repellent, does work but not as well, requiring almost hourly application.

Once you're home, keep an eye on your health for a few weeks. If sudden fever or illness strikes, don't hesitate to call your doctor. And be sure to tell him or her where you've just been.