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On a recent trip to Vietnam, I reluctantly found myself looking for malaria medication in the best "pharmacy" available, a bare room full of unmarked jars of pills down one of Ho Chi Minh City's back alleys. Luckily, neither the pills nor malaria got to me. However, poor planning can pose a threat not only to one's health but also to that of the ecosystems we visit.

While protecting against food-borne illness is your first line of defense, other diseases await unwary travelers. Take care when swimming, as schistosomiasis, carried by parasitic worms, and "swimmer's itch," or cercarial dermatitis, carried by microscopic parasites, are common in freshwater in parts of the Caribbean, South America, Africa and Asia. Malaria-bearing mosquitoes, endemic in West Africa and South Asia, infect 300 to 500 million people worldwide annually, while mosquitoes in Southeast Asia carry dengue fever and those in Africa and South America carry yellow fever. U.S. travel isn't risk-free either; mosquito-borne West Nile Virus claimed 165 U.S. lives in 2006, not to mention rodent-borne hantavirus and tick-transported Lyme disease.

What You Can Do

• Contact your doctor or travel clinic four to six weeks ahead of travel to plan for vaccinations and medications. Pack a medical kit, including needed prescriptions, first-aid supplies, extra medicines and—if you plan to be sexually active—contraceptives.
• Consider medical insurance for travel to destinations with disease and poor sanitation, or for high-risk adventure plans.
• Fend off mosquitoes and other insect bites with long-sleeved shirts, pants and hats. Use repellents sparingly, especially DEET, which can cause skin irritation and blistering at high concentrations. The less-toxic lemon eucalyptus oil in Bygone Bugzz or Cutter picaridin-based repellents also provide long-lasting protection. Bed netting permeated with pyrethroid insecticides, such as the Mombasa Defender Mosquito Net ($26; www.rei.com, 800-426-4840), can be a useful shield, but minimize contact with skin and clothing.
• In tick-infested areas, check yourself during outdoor activity and at day's end.
• Where swimmer's itch or schistosomiasis is prevalent, swim in chlorinated pools or saltwater.

Information and Resources

Centers for Disease Control, Travelers Health Guidance: www.cdc.gov

International Association for Medical Assistance to Travelers: www.iamat.org

International Society of Travel Medicine, Travel Clinic Directory: www.istm.org

Information on Travel Health Insurance: www.insuremytrip.com

U.S. EPA Guidance on Insect Repellents: www.epa.gov