Light micrograph showing eight eggs of the human pinworm (Enterobius vermicularis) parasite. Human pinworm, or threadworm, causes a common intestinal infection called enterobiasis. Pinworm infection is caused by poor hygiene. Human pinworm eggs are deposited on perianal folds, making the area itchy. Self-infection can occur when a person touches the anus and swallows the eggs. Threadworm infection can be treated by improving hygiene and using over-the-counter anthelminitic medicines such as mebendazole and pyrantel pamoate.