Threadworm

🧭 When to suspect

Threadworm (Enterobius vermicularis, “pinworm”) is the commonest helminth infection in the UK and a near-universal childhood experience – up to 40% of children under 10 are infected at any one time. Suspect it in any child (and frequently the wider household) presenting with intense perianal itching (pruritus ani) that is characteristically worse at night, when the gravid female migrates to the perianal skin to lay her eggs.

The diagnosis is usually made on the history alone, or confirmed by a parent seeing small, white, thread-like worms (a few millimetres up to about 1 cm, like moving cotton threads) on the perianal skin or in the stool. In girls, worm migration to the vulva can produce vulvovaginitis, dysuria or vaginal discharge. Infection is frequently asymptomatic, which is why household clustering is the rule rather than the exception.

Transmission is faecal–oral: eggs are swallowed (typically from contaminated fingers after scratching), hatch in the gut, and mature over one to two months. Eggs survive on fingers, bedding and surfaces for up to two weeks, which drives the cycle of re-infection. The two clinical priorities in primary care are simple and reliable: confirm the diagnosis pragmatically, and treat the whole household at once alongside strict hygiene – because no medication kills the eggs.

Source: NHS