Enterobius vermicularis is the human 'pin worm' or 'seat worm and is perhaps the most common parasitic nematode of man throughout the world. It has been reported to occur in chimpanzee also.
Its incidence, however, is greater in women and children. Adult worms live in caecum, appendix and at the junction of small and large intestines. Sexes are separate and there is distinct sexual dimorphism. Worms are slender and cream - colored. Male is 2 to 5 mm long, with a diameter of 0.1 to 0.2 mm. Female is 8 to 13 mm long with a diameter of 0.3 to 0.5 mm. At the anterior end, in both sexes, are 3 lips and a pair of cephalic expansions. Posterior or tail end of female is long and pointed, while that of male is curved, blunt, and with a bursa - like expansion and a single spicule. There is no gubernaculum. Papillae support caudal algae. Male is monorchic and female didelphic. Life cycle is simple and direct. No intermediate host is involved. At night, females with eggs migrate to anus and deposit eggs. This causes severe itching at the anal and perineal areas and the host is tempted to scratch. Tiny eggs, about 55u by 30u and each containing a much developed larva, thus associate with fingers and finger nails and finally enter its gut with food to cause a reinfection. Eggs hatch in duodenum. Larvae reach small intestine, where they moult twice and become adults. Adults live in host for 20 to 30 days. Infection thus automatically dies out within a month provided there is no reinfection. Good sanitary habits are the best weapon against infection. Symptoms of infection are loss of appetite, insomnia, hysteria, restlessness and inflammation of mucous membrane of infected areas.
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