The Travel Bug

Pathogens and People: The travel bug can be infectious By EDWARD McSWEEGAN, For The Capital Published 05/03/09 Summer is approaching and that means it's time to start planning vacations to the far side of the Chesapeake Bay, and the far side of the world. Travel is a seasonal migration worth $1.6 trillion to the U.S. travel and tourism industry. Worldwide, some 2 million people cross international borders every day. At peak times, there are 5,000 planes crisscrossing U.S. skies. In 2007, 458 million people were traveling on vacations. Long-distance travel is a relatively new phenomenon. A few years ago, London epidemiologist David Bradley used four generations of his family to illustrate the expansion of personal travel. His great-grandfather was confined to a 40-kilometer corner of southeast England. His grandfather stretched those boundaries to about 400 km. His father reached the continent (courtesy of the British Army) and wandered over 4,000 km. David, the son, has since extended his own range across six continents and 40,000 km. Great-grandpa would be shocked. Technology has made David's kind of long-distance travel easy. Not surprisingly, the ease and scope of modern travel has created new economic and social consequences. There are also infectious disease consequences because when we pack for a trip we also pack along our microbes. When we arrive, we unpack those germs and pick up new ones as if they were tiny souvenirs. Travel - especially international travel - often encourages a laissez faire exchange of microbes. Usually the exchange is harmless. Sometimes it causes illness (e.g., traveler's diarrhea). Sometimes it sparks an epidemic. During the age of sail, sick passengers usually got better - or died - before their ships ever reached port. The vagaries of wind and tide helped to slow the spread of many infectious diseases. (Four of my ancestors died of "ship fever" (typhus) sailing from Ireland in 1847.) The steam engine changed patterns of disease transmission by quickly moving passengers between ports while some of them were still contagious. A 19th-century sailing trip from India to Fiji took 70 days, but insured any passengers with measles either died or recovered before the ship made landfall. Steamships made the same journey in half the time and carried more passengers. Enough sick passengers survived the trips to ignite devastating measles epidemics in Fiji. Steamships also carried plague-infected rats and fleas around the world in the late 19th century. Bubonic plague from China reached Hawaii in 1899 and San Francisco in 1900. (Plague is still in the U.S. today, having found a comfortable home among the squirrels and prairie dogs of the West.) Modern jets have made the problem of travel and infections much worse. Many long-range planes can now reach almost any part of the globe in 24 hours. That means visitors to West Africa can be exposed to deadly viruses such as Lassa and Marburg, and fly home to the U.S. or Europe before they show symptoms of infection. Eco-tourists can bring home water-borne illnesses such as leptospirosis or amoebic dysentery, rabies or H5N1 influenza from wildlife, encephalitis viruses from ticks and mosquitoes, and rare but deadly hemorrhagic viruses from

bats and rodents. In 2003, jets spread the SARS virus from China to 29 other countries, causing 800 deaths and economic losses of $40-54 billion. In 2007, a U.S. lawyer infected with multidrug-resistant tuberculosis (MDR-TB) created an international panic as he hopped planes, crossed borders and breezed past customs officials. Back on the high seas, modern cruise ships can bring a few thousand passengers together for extended trips. On board, they may be exposed to Legionella in the water systems, influenza in the air, and that bane of all cruises, the highly contagious norovirus, which contaminates food and persists on surfaces. Last year, half a dozen cruise lines experienced outbreaks of norovirus. Bugs like to travel. Should you plan a "staycation" and hide out at home? Well, don't forget the infected ticks and mosquitoes lurking in the backyard. And just because you're not traveling doesn't mean other people won't be. The world is crowded with immigrants, migrants, refugees and foreign tourists. But a little planning and guidance can make for a safer and healthier trip. The Centers for Disease Control and Prevention, for example, has a Web site for traveler's health issues (www.cdc.gov/Travel). ProMED mail (www.promedmail.org) has daily listings of potential disease outbreaks collected from all over the world. HealthMap (www.healthmap.org) collects outbreak reports and displays them on a map. The map can be searched by disease, country and news source. Travel medicine clinics such as Baltimore-based Passport Health (www.passporthealthusa.com) also provide information about overseas disease threats, suggest appropriate medicines and vaccinations, and even sell traveler's insurance against overseas accidents and medical evacuations. Bon voyage. Dr. Edward McSweegan has a Ph.D. in microbiology and lives in Crofton. He works on and writes about infectious disease issues. He may be contacted at [email protected].