IN THE TROPICS
The first thing you need to remember is that food and water-borne diseases are the number one cause of illness in travellers, especiallly those traveling to the tropics – so the best way to enjoy a healthy vacation is to make sure your food and drinking water are safe. While you might be relatively safe travelling aboard a luxury cruise liner, if you're heading ashore to wine and dine, or if you're buying your own groceries for your own private yacht, there are some precautions you might want to consider.
Wash your hands often with soap and water - there are some pretty nasty germs out there - drink only bottled or boiled water, and if in doubt, remember: boil it, cook it, peel it, or forget it!
If you're heading into rural areas, The Center For Disease Control in Atlanta, Georgia, recommends precautions against Hepatitis A, Hepatitis B if you're staying for extended periods, Rabies if you're going into the jungle, Typhoid if you're staying longer than 6 weeks, and Yellow Fever if you're travelling even further afield. If you are visiting an area where there is risk of malaria, take your medication before, during and after travel as directed. It's also a good idea to have a booster of tetanus and measles.
But most of important of all - see your own physician ahead of time. He will have a better grasp of your medical history, and will be able to tell you exactly what you need.