Tropical Illnesses -- Among Southeast Asia's tropical diseases carried by mosquitoes are malaria, dengue fever, and Japanese encephalitis. Reports about malaria prophylactics vary. While most local health agencies tell you not to waste your time with antimalarial drugs, the CDC still advises people to take tablets, most of which cause uncomfortable side effects. In truth, your only sure way to avoid mosquito-borne diseases is to avoid being bitten. Repellents that contain DEET are the most effective, but more gentle alternatives (like baby-care products in any pharmacy) provide DEET-free mosquito protection without the chemicals. Also be aware that malaria mosquitoes bite between the hours of 5 and 7 in the morning and the evening, so it's important to exercise caution at those times (wearing long sleeves and long trousers is a good idea, as is burning mosquito coils). Dengue-fever mosquitoes bite during the day.
Hepatitis A can be contracted from water or food, and cholera epidemics sometimes occur in remote areas. Bilharzia, schistosomiasis, and giardia are parasitic diseases that can be contracted from swimming in or drinking from stagnant or untreated water in lakes or streams.
Anyone contemplating sexual activity should be aware that HIV is rampant in many Southeast Asian countries, along with other STDs such as gonorrhea, syphilis, herpes, and hepatitis B.
Dietary Red Flags -- Unless you intend to confine your travels to the big cities and dine only at restaurants that serve Western-style food, you will likely be sampling some new cuisine. This could lead initially to upset stomach or diarrhea, which usually lasts just a few days as your body adapts to the change in your diet.
Except for Singapore, where tap water is safe to drink, always drink bottled water and never use tap water for drinking or even brushing teeth. Peel all fruits and vegetables and avoid raw shellfish and seafood. Also beware of ice unless it is made from purified water. (Any suspicious water can be purified by boiling for 10 min. or treating with purifying tablets.)
If you're a vegetarian, you will find that Southeast Asia is a great place to travel; vegetarian dishes abound throughout the region. In terms of hygiene, restaurants are generally better options than street stalls, but don't forgo good local cuisine just because it's served from a cart. Be sure to carry diarrhea medication as well as any prescription medications you might need. It's acceptable to wipe down utensils in restaurants, and in some places locals even ask for a glass of hot water for just that purpose (some travelers even carry their own plastic chopsticks or cutlery). Bringing antiseptic hand-washing gel is also not a bad idea for when you're out in the sticks.
So, how can you tell if something will upset your stomach before you eat it? Trust your instincts. Avoid buffet-style places, especially on the street, and be sure all food is cooked thoroughly and made to order. If your gut tells you not to eat that gelatinous chicken foot, don't eat it. If your hosts insist but you're still afraid, explain about your "foreign stomach" with a regretful smile and accept a cup of tea instead. Be careful of raw ingredients, common in most Asian cuisines, but realize that questions like, "Are these vegetables washed in clean water?" are inappropriate anywhere. Use your best judgment or simply decline.
Bugs, Bites & Other Wildlife Concerns -- There are all kinds of creepy critters to be aware of in any tropical climate. In rural accommodations, mosquito nets are often required and, if so, are always provided by hoteliers. Check your shoes in the morning (or wear sandals) just in case some ugly little thing is taking a nap in your Nikes. Keep an eye out for snakes and poisonous spiders when in jungle terrain or when doing any trekking. Having a guide doesn't preclude exercising caution. Rabies is rampant, especially in rural areas of the less-developed nations, and extreme care should be taken when walking, particularly at night. In places like Thailand, dogs are simply fed and left to roam free, and you are likely to run into some ornery mutts. A walking stick or umbrella is a suitable deterrent when out in the countryside. It's also important to know that all dogs have been hit with hurled stones sometime in their life, and, a nod to Pavlov here, the very act of reaching to the ground for a handful of stones is often enough to send an angry dog on the run, for fear of being pelted. If you are bitten, wash the wound immediately and, even if you suffer just the slightest puncture or scrape, seek medical attention and a series of rabies shots (now quite a simple affair of injections in the arm in a few installments over several weeks).
Respiratory Illnesses -- SARS hit the region hard in the winter and spring of 2003. Singapore reported some cases and essentially closed to tourism, and though most other countries in the region reported no cases of the disease, places like Thailand suffered the fallout of the regionwide scare. There have been no reported cases of SARS since 2004. Tuberculosis is a concern in more remote areas where testing is still uncommon.
The avian influenza, also called the bird flu, is another public-relations nightmare in Southeast Asia. A number of cases have been reported in Thailand and Vietnam, and millions of chickens suspected of carrying the illness have been slaughtered. The victims of the bird flu have been few in number (statistically insignificant, really) and are mostly isolated to people working in the poultry industry. The countries affected have been unusually forthright about reporting new cases, and the disease is yet limited in scope. It is important to note that you cannot contract bird flu from consuming cooked chicken.
Air quality is not good in the larger cities like Bangkok or Ho Chi Minh City; with no emissions standards, buses, trucks, and cars belch some toxic stuff, so visitors with respiratory concerns or sensitivity should take caution.
Sun/Elements/Extreme Weather Exposure -- Sun and heatstroke are a major concern anywhere in Southeast Asia. Limit your exposure to the sun, especially during the first few days of your trip and, thereafter, from 11am to 2pm. Use a sunscreen with a high protection factor, and apply it liberally. Asians are still big fans of parasols, so don't be shy about using an umbrella to shade yourself (all the Buddhist monks do). Remember that children need more protection than adults.
Always be sure to drink plenty of bottled water, which is the best defense against heat exhaustion and the more serious, life-threatening heatstroke. Also remember that coffee, tea, soft drinks, and alcoholic beverages should not be substituted for water because they are diuretics that dehydrate the body. In extremely hot and humid weather, try to stay out of the midday heat, and confine most of your daytime traveling to early morning and late afternoon. If you ever feel weak, fatigued, dizzy, or disoriented, get out of the sun immediately and go to a shady, cool place. To prevent sunburn, always wear a hat and apply sunscreen to all exposed areas of skin.
Be aware of major weather patterns; many island destinations are prone to typhoons or severe storms.
