5. Opisthorchis viverrini – Opisthorchis viverrini is a major problem in regions of Southeast Asia, particularly Thailand, Vietnam, Cambodia, and Lao PDR. Not only does it present a heavy economic toll on the people and the government, but its health toll is great too, potentially causing a wide variety of diseases, including cancer of the bile ducts.
4. Vandellia cirrhosa – While this dreaded creature (known more commonly as the candiru) is the work of many a tall tale, venturing into the wrong area could have you dealing with this creature. The candiru is a fairly well-known parasite, due to the horror of it – a parasite that enters a person's urethra. At which point, the candiru more than earns nicknames such as the “toothpick fish” and the “vampire fish”, inflicting a dreadful level of pain unto its host.
3. Filarial parasites – These parasites can be transferred through mosquito bites, as though mosquitoes weren't annoying enough. If you've ever seen The Elephant Man, you should have an idea of what this can do. If not, well… just hope to goodness that you don't get elephantiasis, lest you want various parts of your body to swell to gargantuan sizes.