Infection is seen when the adult worm emerges through the skin of an infected person.
Worms grow up to 3 feet long and are as wide as a paper clip wire. About 10 days after the water flea ingests them, the water fleas become infective to anyone who swallows them. Once swallowed, stomach acid digests the water flea, but not the Guinea worm. The Guinea worm then grows to adulthood, a process that takes about a year. Infected persons do not usually have symptoms until about 1 year after they drink contaminated water.