=enterobius. Common in young children, probably due to hygiene issues. Also called pinworms. Small (1-2cm), like white threads. Can be intensely itchy, usually in night when worms emerge to lay eggs.

Mebendazole effective at killing live worms in gut, not effective if eggs in vagina. Licensed from age 2 but can be used off license below that. Does not kill eggs however, and main issue is reinfection so consider treating whole family, with repeat doses after 2 weeks when any eggs will have hatched. NHS Inform advice on hygiene:

• Lifespan of threadworms is approximately 6 weeks, so follow hygiene measures for at least this length of time.
• Everyone in the household must follow the advice outlined below.
• Wash all night clothes, bed linen, towels and soft toys (normal temperatures OK but make sure the washing is well rinsed [presumably at start of treatment; dilution more important than soap?]
• Vacuum and dust the whole house esp bedrooms – repeat regularly
• Clean bathroom and kitchen surfaces – again, rinse cloth frequently – repeat regularly
• Avoid shaking out clothes/bedding that may be contaminated with eggs, to prevent eggs being transferred to other surfaces
• Don’t eat food in the bedroom
• Keep fingernails short
• Discourage nail-biting and sucking fingers/thumbs
• Wash hands frequently and scrub under your fingernails esp before eating, after going to the toilet, and before and after changing your baby’s nappy
• wear close-fitting underwear at night and change your underwear every morning
• bathe or shower regularly – it’s particularly important to bathe or shower first thing in the morning: make sure you clean around your anus and vagina to remove any eggs
• don’t share towels
• keep toothbrushes in a closed cupboard and rinse them thoroughly before use!

Eggs probably become unviable after a few days if not in warm and moist environment… Children may of course pick up another threadworm infection from school/nursery…

Sometimes you just have to keep repeating treatment over months/years! Mebendazole is harmless (v little systemic absorption), although symptoms may be caused by clearance of large worm burdens.