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Pinworm life cycle

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Life span pinworms

People have pinworm infection by unknowingly eating microscopic pinworm eggs. The eggs pass into the digestive system and hatch in the small intestine. From the small intestine, pinworm larvae continue their journey to the large intestine. During this migration they moult twice and become adults.

Females survive for 5 to 13 weeks and males about 7 weeks. The male and female pinworms mate in the ileum whereafter the male pinworms die and are passed out with stool. The gravid female pinworms settle in the ileum, caecum, appendix and ascending colon, where they attach themselves to the mucosa and ingest colonic contents. Almost the entire body of a gravid female becomes filled with eggs. The estimations of the number of eggs in a gravid female pinworm ranges from about 11,000 to 16,000. The gravid female pinworms migrate through the colon towards the rectum at a rate of 12 to 14 centimeters per hour. The reason the female emerges from the anus is to obtain the oxygen necessary for the maturation of the eggs.

Eggs are deposited on perineal folds and the female pinworms die.

Self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perineal 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 When someone scratches the itchy area, pinworm eggs are transferred to their fingers. Contaminated fingers can carry pinworm eggs to many different surfaces, including bed linens, towels, clothing (especially underwear and pajamas), toilets and bathroom fixtures, drinking glasses and eating utensils, toys, sandboxes and food. Pinworm eggs are able to live on a surface for 2-3 weeks, especially in a humid environment, and can contaminate other persons. Finger sucking has been shown to increase both incidence and relapse rates and nail biting has been similarly associated.

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.

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 pinworm adult is about two months. Gravid females migrate nocturnally outside the anus and deposit while crawling on the skin of the perineal 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.

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