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http://query.nytimes.com/gst/fullpage.html?res=9403E2DA1639F93BA15757C0A96095...

PRACTICAL TRAVELER;Pesky Parasites And Nasty Bites

The New York Times

By BETSY WADE

Published: April 28, 1996

THREE diseases you may never have heard of -- and your doctor may not recognize -- are among those that can lay you low in the aftermath of a trip to the tropics, or even to a United States national park. There are no vaccinations or pills that prevent these three: schistosomiasis, a parasite disease also known as bilharzia, or snail fever; giardiasis, frequently called giardia, for the parasite that causes it, and dengue, or breakbone fever.

Avoiding these diseases requires behavior modification, which Dr. Mary Wilson, author of "A Guide to World Infections" (Oxford University Press, 1991) says is more difficult than taking shots. Safe behavior is based on knowing what and where the dangers are.

Swimming in fresh water in the tropics can cause schistosomiasis. Drinking contaminated water (or using ice cubes made from it), including water in streams in wildlife areas, can cause giardiasis. Mosquitoes carry dengue. Travelers who have been to areas where these diseases are found and who feel ill should see a doctor for tests and treatment.

There are no data on how many travelers contract these diseases, although Dr. Phyllis Kozarsky, secretary-treasurer of the International Society of Travel Medicine, says that the incidence of schistosomiasis, which sometimes has no symptoms, is much higher than had been thought: 20 patients showed up with it last year at her clinic in Atlanta.

Here is a closer look at these diseases and some information about how to avoid them.

Dengue

The risk of contracting dengue has been rising. Dr. Gary Clark, a dengue specialist at the Federal Centers for Disease Control and Prevention in San Juan, P.R., estimates that 100 cases come back to the United States each year from abroad, but 10 locally acquired cases were reported in the border area of Texas last year. Dengue is transmitted by the bite of a mosquito that has bitten someone with the fever. There are millions of cases worldwide each year.

Dengue has a sudden onset, with high fever, a rash, severe headache, muscle and joint pain -- hence "breakbone fever." Nausea and vomiting and loss of appetite are common. Like malaria, it can look like flu to a doctor. The fever lasts three to seven days, and the convalescence may be long. A tourist who picked up dengue in Ixtapa, Mexico, was so sore he couldn't walk by the time he got back to New York, and was unable to work for six months. He still had muscle problems a year later and complained that his resistance was low.

Severe complications are rare in classic dengue fever, as opposed to the hemorrhagic type, which can be fatal, but this is not usually a risk for travelers since it derives from a second infection from another dengue virus; there are four types of dengue virus. There is no specific treatment for the nonhemorrhagic versions.

Dengue is found in most of tropical Asia, the Pacific islands, the Caribbean, Central and South America and Africa. The mosquitoes that transmit it live in close association with humans, breeding in discarded tires, flower pots, old oil drums and cisterns. Unlike malarial mosquitoes, dengue mosquitoes, usually Aedes aegypti, bite in the daytime.

A major factor in the rise in dengue, Dr. Clark said, is jet air travel. A traveler bitten in Thailand boards a flight to Boston feeling fine but incubating the disease. In Boston another mosquito bites that traveler and begins transmitting the virus. The incubation period ranges from five to eight days.

Dr. Wilson, chief of the infectious diseases section at Mount Auburn Hospital in Cambridge, Mass., said doctors should rule out malaria first when a patient has been to the tropics. Malaria is life-threatening and there are specific treatments. Dengue can be identified by a blood test. Simple dengue is painful but not fatal, and is treated by keeping the patient resting, comfortable and drinking lots of fluids. The patient should be kept away from mosquitoes for the protection of others.

Avoiding dengue means avoiding mosquito bites. Use of a mosquito repellent with 20 to 30 percent DEET is recommended. Wearing long-sleeved shirts and long pants is helpful, and clothing can be sprayed or dipped in the insecticide permethrin. A Government pamphlet, "Preventing Dengue Fever in Travelers," notes that the risk is reduced if travelers stay in air-conditioned buildings or other closed environments, avoid heavily populated residential areas, and spend outdoor time on beaches or forested areas where the risk of infected mosquitoes is less.

The pamphlet is free on request to Dengue Branch, National Center for Infectious Disease, 2 Calle Casia, San Juan, P.R. 00921-3200; (809) 766-5181, fax (809) 766-6596.

Schistosomiasis

A fresh-water parasite found in the Caribbean, South America, Africa and Asia causes schistosomiasis, another disease that is on the rise -- particularly because of projects bringing fresh water into dry lands. Estimates are that 200 million people in at least 74 countries are infected, and the World Health Organization puts the annual death rate at 200,000. The International Association for Medical Assistance for Travelers, a volunteer group, reports that the incidence of the disease in Ghana jumped from 5 percent of the population to 7 percent after construction of a dam on Lake Volta.

Dangerous areas for travelers are Brazil, Puerto Rico and St. Lucia, Egypt and most of sub-Saharan Africa, southern China, the Philippines and Southeast Asia.

The flatworm that causes this disease uses fresh-water snails as the intermediate host. The snails release larvae into the water, and these enter humans through the skin in 30 seconds to 10 minutes. There may be no symptoms initially; if there are, those exposed for the first time may have fever, chills, cough, diarrhea, weakness and headaches. But many people who get a chronic form, with involvement of the lungs, liver, intestines and bladder, may recall no acute symptoms after exposure.

Once diagnosed through blood and other tests, the disease is treated with a single dose of a drug, praziquantel, which the doctors interviewed say is easily tolerated. But for those who are untreated for a long time, it can be hard to cure and there may be lifelong complications.

Twenty-two Israelis who traveled to Africa in 1993-94 and later visited two travel clinics in Haifa all tested positive for schistosomiasis, some with no symptoms at all. When their histories were taken, it turned out that all had swum in Lake Malawi in Malawi, some despite a warning about the risk of contracting the disease in any fresh water in the area, including bath water that has not stood for three days.

Various travel publications have incorrectly stated that Lake Malawi was free of bilharzia -- including the fifth edition of "Africa on a Shoestring," published by Lonely Planet (corrected in later editions), and the Travel section of The New York Times in an article on Dec. 31 (a correction was published on Jan. 7). But the Centers for Disease Control in Atlanta has confirmed its presence, and the most recent State Department consular information sheet about Malawi warns of it.

Giardiasis

The most common source of chronic diarrhea picked up while traveling is giardiasis, Dr. Wilson says. At one point, Leningrad was considered a prime spot for catching giardiasis, diarrhea caused by the parasite giardia: 23 percent of Americans who visited there between 1969 and 1973 got it. The Centers for Disease Control issued a warning on March 12, 1986, about giardia in the water in all of the then Soviet Union, particularly Leningrad, now again St. Petersburg. This warning remains in effect, according to Rosamond R. Dewart, chief of the travelers health section, because of uncertainty about the health infrastructure in the new Independent States.

But giardiasis can be caught anywhere in the world; the hiking leaflets in Glacier National Park in Montana warn about giardia in the water there, and ski resorts in the West frequently suffer outbreaks after the spring melt, when water overflows the sewage systems and gets into the drinking supply.

Routine chlorination does not kill giardia. Nor does freezing, as a physician discovered in Thailand when he forgetfully put an ice cube into his scotch. Boiling water does.

It is exasperating to have to drink bottled water while climbing past beautiful streams and falls, but that is what must be done.

The parasite lodges in the upper intestine and is hard to get rid of, so diarrhea may persist. Dehydration can be a serious problem for children, and they should get lots of liquids while recovering. But the disease is not fatal and there are prescription medications that doctors will prescribe to treat it: quinacrine hydrochloride, metronidazole and furazolidone. In addition, there is tinidazole, which is not available in the United States.

The newest edition of the Centers for Disease Control book "Health Information for International Travel" is available for $14 from the Superintendent of Documents, United States Government Printing Office, Washington, D.C. 20402; (202) 512-1800.

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