Enterobiasis

Enterobiasis is caused by the pinworm Enterobius vermicularis. This nematode is probably the most common parasite to host on humans because it flourishes in temperate and tropical climates.

The small, spindle-shaped, white round adult worms inhabit the cecum and appendix, and adjacent parts of the large and small intestines; their heads attach to the intestinal mucosa. A male worm measures 2 to 5 mm in length, and the female 9 to 11 mm. The female produces eggs in its ovary and releases them into a reservoir, or uterus, where fecundation takes place. When the reservoir is filled, the worm detaches itself from the bowel wall and migrates down the colon to the rectum. Some parasites are expelled with feces, but others migrate through the anal canal and, while crawling, deposit eggs in the perianal and the genitocrural folds. On average, one female deposits 11,000 eggs. Within hours of passage, the eggs enter an infective stage, and they may be passed to humans by hand contact, from sheets and pillowcases, or directly onto food and water ( Fig. 118.1 ; see also Fig. 123.1 ). Once the eggs are ingested, the larvae escape from the eggs into the stomach and the duodenum, molt twice, and pass into the large intestine to complete the life cycle.

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Enterobiasis: Life Cycle of Enterobius vermicularis Nematode (Pinworm).