Transmission
Transmission of E. vermicularis occurs when worm eggs are ingested. This mode of transmission is therefore described as having an oral-anal route. When infested humans experience perianal itch due to the ovipostion of eggs in their perianal folds, they often scratch the perianal area and get the pinworm eggs on their fingers or under their fingernails. Fingers are an ideal location for transmission of the nematode, as patients can either transfer the eggs to their own mouths (this is called autoinfection) or to other humans. The tendencies for children to engage in finger sucking and to touch their peers make transmission of pinworm between preschool and elementary school-age children especially common.
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While pinworm infestation is extremely prevalent among pediatric hosts, adults are also often affected, especially when they live with young children. In fact, entire families are frequently diagnosed with pinworm all at once. The common occurrence of familial outbreaks can be explained by the ability of pinworm eggs to persist on the bedding and clothing of the infested child. When parents handle the contaminated sheets, underwear, or shared family items, they get the ova on their fingers and are then capable of transferring the worm eggs to their mouths.
Other less common modes of transmission have been recorded as well. “Retrofection” is said to occur when embryonated eggs hatch after being deposited in the perianal folds of the host and then travel through the anus and directly back up the gastrointestinal tract. Inhalation of dust containing pinworm eggs has also been identified as a mode of transmission, although air-borne infestation is extremely rare.