The parasites you're most likely to hear about — what each one actually is, how you get it, and the tell-tale sign — in plain English. This is the quick-reference version; each entry links to the fuller page.
A microscopic parasite that causes watery diarrhea (cryptosporidiosis). You usually get it by swallowing contaminated water — pools and lakes are the classic sources. Most healthy people recover on their own. More on watery diarrhea →
A microscopic parasite spread through contaminated fresh produce; it causes prolonged, relapsing watery diarrhea and is behind the recent produce-linked outbreaks. More on the Cyclospora outbreak →
A microscopic parasite of the small intestine — the classic cause of greasy, foul-smelling diarrhea and bloating, often from untreated lake or stream water. More on bloating & Giardia →
A small worm that enters through bare skin from contaminated soil and feeds on blood, which can cause anemia over time. Wearing shoes is the simple guard. More in the human parasites guide →
A single-celled organism in warm fresh water. It causes an extremely rare but serious brain infection — only when water is forced up the nose, never from drinking. More on the brain-eating amoeba →
The most common worm infection in the United States — tiny white, thread-like worms. The classic sign is anal itching that's worse at night, especially in children. Very treatable. More on night-time itching →
The most common worm parasite found in humans, swallowed as eggs from contaminated soil or unwashed produce. Light infections often cause no symptoms at all. More in the human parasites guide →
A parasite that completes its life cycle in cats, spread through cat feces or undercooked meat. Most healthy people never have symptoms — it matters most in pregnancy. More on pets & zoonotic risk →
A soil-transmitted worm caught by swallowing eggs from contaminated soil. Often symptomless; heavier infections can cause ongoing digestive symptoms. More in the human parasites guide →
Compare your symptoms against the common, ordinary look-alikes.
Symptoms guide →The parasites worth knowing, in 30 seconds.
Is It a Parasite? — four pages, plain English, from CDC and WHO sources. The red flags and a printable prevention checklist.
