pinworms
Tiny pinworms are the most common roundworm parasites of people in the U. S. In some areas, as many as one out of three children are infected. Humans become infected when they ingest the nearly microscopic pinworm eggs. The eggs hatch and develop into adults in the hosts digestive tract. Adults lay eggs that pass out of the hosts body to continue the cycle. Pinworms have a fairly simple life cycle with only one host.