route of threadworm infection is generally via human ingestion of an an ova
the eggs contain a partially developed juvenile that can develop to infectivity within 6 hours at body temperature, are swallowed and hatch in the duodenum
once ingested the immature worms move slowly down the small intestine and are adults by the time of their arrival at the ileocecal junction
total time from ingestion to sexual maturity is 15–43 days (1)
the adult worms generally congregate in the ileocecal region; however may wander throughout the gastrointestinal tract
adult worms attach to the mucosa and feed upon epithelial cells and bacteria
gravid females begin migrating within the lumen and passing out of the anus onto the perianal skin
as the females crawl, they leave a trail of eggs
a single female worm may deposit 4,600–16,000 eggs
female worms may literally explode and liberate masses of eggs
female worms die after oviposition
male worms die after copulation
eggs are infective within 6 hours. In ideal conditions the eggs may remain infective for up to 20 days
human infection occurs via either:
faecal-oral transmission by contaminated fingers or fomites
airborne infection via through airborne eggs that are dislodged from bed linens and clothes
retroinfection - in this form of infection threadworm larvae that hatch on the anus then crawl back into the rectum and bowel to mature and mate
reinfection by any of these methods can result in an extremely heavy parasite load within the host
Notes:
humans are the only host for threadworms - threadworm infection cannot be transmitted by dogs and cats because these animals are free of threadworm infection. However the fur of animals can pick up eggs from the environment and be a source of infection
sources of reinfection include clothing, bedding, curtains, walls, and carpets become sources of reinfection. There have been reports of eggs having been found in the dust of schoolrooms and school cafeteria (1)
Reference:
L.S. Roberts , Nematodes: Oxyurida, the pinworms. In: L.S. Roberts and J. Janovy, Editors, Foundations of parasitology, McGraw Hill, Boston (2000), pages 433–437.
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