Travel is one of the most common ways people actually acquire parasites, usually through food, water, or soil. A little planning before you go, and a simple screen when you return, prevents most problems and catches the rest early.
Most travel-acquired parasites are protozoa like Giardia, Cryptosporidium, and Entamoeba, plus some helminths in specific regions. They arrive via untreated water and ice, raw or undercooked food, unwashed produce, and walking barefoot on contaminated soil or beaches. The classic sign is digestive trouble that starts during or shortly after a trip and won't settle.
Risk rises with rural travel, longer stays, adventure or volunteer trips, and regions with limited water sanitation: much of South Asia, sub-Saharan Africa, and parts of Latin America and Southeast Asia. But even short city trips carry some risk from food and ice, so it's worth a quick assessment rather than a guess.
Check destination health advisories, see a travel clinic if needed, pack water purification and oral rehydration salts, and learn the local food-and-water rules. Some trips warrant prescription stand-by medication, so ask your doctor.
"Boil it, cook it, peel it, or forget it." Drink sealed or treated water, skip ice and raw salads in high-risk areas, wear footwear on soil and beaches, and wash hands before eating. Most infections trace back to one avoidable meal.
If you had diarrhea abroad or it appears within weeks of returning, don't self-treat. Get a stool test instead. Persistent symptoms after travel are the textbook reason to test, since the right treatment depends on the exact parasite.
Prevention while traveling is really just everyday prevention turned up a notch. If you do come home with symptoms, start with testing before any treatment or cleanse, and only then weigh medical or natural options.