Travel is one of the most common ways people actually pick up a parasite, but the precautions are simple and the payoff is large. You do not need to treat every meal abroad as a threat. You need to understand the three routes that matter and build a few easy habits around them.
The three routes that matter
Most travel-acquired parasites arrive by one of three paths: contaminated water and ice, raw or undercooked food and unwashed produce, and barefoot contact with contaminated soil. Protozoa such as Giardia are the usual culprits, and they are good at lingering long after a trip ends.
The old travel maxim still does most of the work: boil it, cook it, peel it, or forget it. Almost every practical rule below is a version of that idea.
Water and ice
In higher-risk regions, drink sealed bottled water or water you have treated yourself by boiling, filtering, or using purification tablets. The easiest mistake to make is the ice in an otherwise careful drink, so skip it when you are unsure of the water it came from.
Brushing your teeth with tap water counts too. Use treated or bottled water for that in places where the supply is not reliable.
Food and produce
Hot, freshly cooked food served steaming is usually your safest bet. Raw salads and unpeeled fruit washed in local tap water are a common source of trouble, so favor fruit you peel yourself and vegetables that have been cooked.
This is about probability, not fear. You are simply tilting the odds in your favor at each meal.
Soil, feet, and before you go
Some worms enter through the skin of bare feet, so wear footwear on soil and beaches in warm, moist regions. Before a trip, a quick visit to a travel clinic is worth it for higher-risk destinations, and packing oral rehydration salts means a bout of traveler's diarrhea is far less miserable.
If you do get sick during or shortly after a trip and it will not settle, do not reach for a cleanse. Get a stool test, because the right treatment depends on knowing exactly what you picked up.
Prevention while traveling is just everyday prevention turned up a notch, applied one meal and one glass of water at a time.
The bottom line
A handful of habits around water, food, and footwear prevents the large majority of travel infections, and a simple screen on the way home catches the rest early. For the full destination-by-destination version, see our travel health guide, and if symptoms appear after you return, start with testing rather than self-treatment.