Pruritus ani is caused by:
a. Pruritis ani is the most common manifestation of oxyuriasis caused by Enterobius vermicularis (pin worm, thread worm). The definitive and the only host in its life cycle is man. Habitat is caecum.
b. Eggs are deposited on perianal folds. Self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perianal area. Person-to-person transmission can also occur through handling of contaminated clothes or bed linens.
c. Enterobiasis may also be acquired through surfaces in the environment that are contaminated with pinworm eggs (e.g., curtains, carpeting).
d. Some small number of eggs may become airborne and inhaled. These would be swallowed and follow the same development as ingested eggs. Following ingestion of infective eggs, the larvae hatch in the small intestine and the adults establish themselves in the colon.