Pinworms are extremely common.
It is estimated that up to 42 million people in the U.S. have this parasite in their intestines. They have been discussed in circles that go as far back as the physicians in ancient Rome and Greece. But it wasn't until the 1930's and 40's when the National Institutes of Health extensive studied this organism. Much of what we know today comes from that research. The eggs reach the intestines where they hatch.