Traveling to Southeast Asia raises a variety of health concerns. My first bit of advice is talk to your doctor - my experiences are mine and mine alone, so you should always check with your doctor on all health related issues when traveling to exotic places. With that said, here are some of the issues we considered:
Traveler's Diarrhea. Wherever you go in the world, stomach ailments seem to follow you. Montezuma's Revenge, Delhi Belly, Cairo Cramps, Bangkok Surprise - they're all some of the many forms of traveler's diarrhea. Even if you're absolutely careful about what you eat and drink, you may still get it for a few days. The easiest way to avoid stomach upset is to never drink the water unless you yourself open a sealed bottle of purified water, which is easily available everywhere. Never use ice, and avoid any food that isn't cooked or peeled - salads are out. Since you'll be eating a lot of rice in Asia, make sure it's steaming hot - if not, send it back, because it could be older than you think. As added protection, we always bring a large supply of bismuth tablets - that's right, Pepto Bismol. The general rule is if you take one dose before every meal, plus one at bedtime, you'll decrease the chance of getting diarrhea. You're tongue will turn black from all the bismuth in your system, so don't be freaked out.
If you're unlucky enough to get sick, all you can really do is deal with it. Take it easy for a couple of days, snack lightly on starchy food like crackers or bread, drink lots of water (avoid alcohol and anything with lots of caffeine!), and don't eat fatty foods. Your body will probably reject everything you give it for a few days, so it's vital you drink lots of fluids, and if necessary, supplement your water with an electrolyte solution - it'll contain all the salts and nutrients your body needs. If you can't find electrolyte solution at a local pharmacy, you can always drink weak tea with a little lemon and some sugar. It's not perfect, but it will help you get back on your feet.
Malaria. As with other tropical parts of the world, malaria is a serious concern in Southeast Asia, especially if you are going to spend any time out in rural areas. Malaria is a vector-borne illness - in other words, you get it from mosquitoes sticking their little probosci into your skin. If I may repeat my earlier advice, please talk to your doctor about malaria.
There is no vaccine for malaria, but you can take several precautions. First, don't get bitten by mosquitoes. I know, easier said than done, but you can avoid significant bites through two types of repellent. For your skin, you'll need to get a buy spray that contains the chemical compound DEET. The amount of DEET in any given repellent ranges from a few percent to 100%, depending on the brand. The Centers for Disease Control recommend a spray with 30%-35% DEET. Admittedly, when we travel, we usually bring something slightly weaker - around 20% - because I personally found higher strength DEET sprays to be irritating on the skin after a few days. But again, that's my personal choice, so don't necessarily listen to me on this particular point. Whenever you're in a malaria-infested area, especially from dusk to dawn (when malaria mosquitoes are out in force), make sure all exposed skin is covered with spray. And never spray DEET directly on your face - either spray some in your hand and wipe it on your face, or use a DEET cream instead of a spray.
Another great way to avoid malaria is to use Permethrin, a powerful anti-bug chemical commonly known under the brand name Duranon. Permethrin is used on your clothes (as well as sleeping bags, sheets, etc., if you bring them). Before you depart for a malaria zone, spray Permethrin according to the directions on the outer layer of all of your clothes (never on the inside layer or underwear - you don't want this stuff touching your skin). It will take several hours to dry completely. Once your clothes are sprayed, they should repel mosquitoes and other nasty bugs for several weeks. Under no circumstances should you ever spray Permethrin on your skin. It's dangerous stuff. Permethrin can be found in most camping supply stores - just look for yellowish green bottles with the name Duranon.
The second way you can avoid the effects of malaria is to take a malaria prophylactic. No, it's not what you're thinking. A malaria prophylactic is prescription medicine that helps control the symptoms of the disease. Since you can't totally prevent malaria (unless you stay home maybe), prophylactics will keep your symptoms under control until you get home. Granted, the vast majority of people who take malaria prophylactics never get the disease, but it's better safe than sorry, right? As I mentioned earlier, you should talk to you doctor about which prophylactic you should take. There are several strains of malaria around the world, and some prophylactics work better with different strains. For example, the malaria found in most of Laos is best attacked with a drug called Lariam (generic name Mefloquine), a pill you take once a week. In Thailand, though, the drug of choice is Doxycycline, an antibiotic you take once a day. Since Lariam works best in most of the world, it's the one most commonly prescribed, but it's also expensive and can cause nightmares in some people.
During our 1996 trip to India we took Lariam, and as far as we know we never got Malaria. For Southeast Asia, though, we decided to opt for Doxycycline. Doxycycline is the prophylactic of choice for rural Thailand, and even though we were going into Laos and Cambodia (both countries are Lariam territory), Doxycycline still makes an acceptable alternative to Lariam. Some doctors would have preferred us to take both medicines, but mine agreed we would probably be fine with only Doxycycline. An added bonus to using Doxycycline is its general antibiotic powers - it also kills many of the potential stomach bugs you might get during your trip. As it turned out, neither of us got sick in Southeast Asia, though this wasn't the case when we traveled to India and the Mideast - perhaps Doxycycline made the difference. One side effect to Doxycycline, though, is that it also kills the good bacteria in your stomach that help you digest food. Our solution to this was to take over the counter yogurt pills, each containing millions of bifidus and acidophilus bacteria - the "good" bacteria in your body. These pills replenished any bacterial losses incurred by the antibiotics.
Other Diseases to Worry About
Dengue fever is a relatively uncommon, yet nasty illness also spread by mosquitoes. Mild forms of the fever involve high fever, but stronger strains occasionally cause epidemics that kill people. There is no vaccine or cure for dengue, so be sure to avoid mosquito bites, using DEET spray and Permethrin as described above.
Hepatitis A is a common yet serious disease you can get anywhere in the world. It's spread by consuming food that has been handled by people who didn't wash properly after using the bathroom (gross, but true). There are two common preventatives for Hepatitis A - Immune Globulin (IG) and Havrix. IG is a shot you take just before your trip. It's relatively cheap but it only last a few months. Havrix is actually two shots - one initial shot and then a booster six months later. It's significantly more expensive than IG, but it's good for at least 10 years. On this trip, Susanne took IG, though I opted for the Havrix. Again, ask your doctor!
I could go on for pages about medical concerns and Asia travel, but I won't since (as I keep saying over and over) you should really rely on a professional's advice. There are other vaccines you may need, but in our case these were the only ones we got this year because we were up-to-date from previous trips. Always talk to your doctor before traveling abroad. You should also visit the Centers for Disease Control travel website, which contains lots of great information including medical recommendations for every country and region on earth. So if you visit the site be sure to check out the Southeast Asia page as well as the pages on malaria, traveler's diarrhea and Hepatitis A. The CDC also hosts the Yellow Book, a reference guide to the risk of malaria in individual countries.