.
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. Enterobiasis may also be acquired
through surfaces in the environment that are contaminated with pinworm eggs
(e.g., curtains, carpeting). 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
.
The time interval from ingestion of infective eggs to oviposition by the
adult females is about one month. The life span of the adults is about two
months. Gravid females migrate nocturnally outside the anus and oviposit
while crawling on the skin of the perianal area
. The
larvae contained inside the eggs develop (the eggs become infective) in 4 to
6 hours under optimal conditions
.
Retroinfection, or the migration of newly hatched larvae from the anal skin
back into the rectum, may occur but the frequency with which this happens is
unknown.