Worm infections in children – particularly threadworm – are extremely common. Many parents are understandably alarmed when they discover a child has worms, assuming this reflects poor hygiene or indicates something unusual about their child. In fact, threadworm infection is so widespread in childhood that having it at some point is close to the norm. Understanding the infection, its treatment, and what can be done to prevent reinfection removes a great deal of the associated anxiety.
Healthbooq covers children's health and common infections in the early years.
Threadworm: By Far the Most Common UK Worm
Enterobius vermicularis – threadworm, also called pinworm – is a tiny, white, thread-like worm about 5-10mm long. Adult female worms live in the large intestine and migrate out of the anus at night to lay eggs in the perianal skin. This nocturnal egg-laying is what causes the characteristic intense perianal itching at night. The eggs are microscopic, invisible to the naked eye, and extraordinarily persistent: they can survive on surfaces for up to 3 weeks under favourable conditions.
Infection occurs via the faecal-oral route. A child scratches their itchy bottom, picks up eggs under their fingernails, and then transfers the eggs to their mouth directly or via surfaces (toys, bedding, food). Entire households are typically infected, as eggs spread readily via shared surfaces, bedding, and towels.
Recognising Threadworm
The most characteristic symptom is perianal itching at night, which can be severe enough to disrupt sleep. Some children scratch to the point of causing skin trauma and secondary infection. A child may also have general irritability and disturbed sleep even without articulating where the itchiness is.
The worms themselves can sometimes be seen in the perianal area at night (with a torch) or in freshly passed stool – white, thin, and wriggling. Seeing the worm is diagnostic and means stool testing is not necessary.
Treatment
Mebendazole is the first-line treatment for threadworm in children over 2 years and adults. It works by inhibiting the worms' uptake of glucose, killing them. A single dose is given, with a repeat dose 2 weeks later to catch any newly hatched worms.
Mebendazole is not recommended in pregnancy or in children under 2 years; in these groups, hygiene measures alone are used with reassessment.
Critically, all household members should be treated simultaneously, regardless of whether they have symptoms. Asymptomatic household members harbour worms just as often as symptomatic ones, and treating only the symptomatic child without treating others leads to rapid reinfection.
Hygiene Measures
Medication alone is often insufficient if hygiene measures are not implemented alongside it. Because eggs can persist on surfaces for weeks, a strict programme must accompany treatment:
Short fingernails: cutting nails short and scrubbing under them removes the main reservoir of eggs. This should be maintained for 6 weeks.
Hand washing: thorough handwashing after toileting and before eating, every time, for 6 weeks.
Morning bathing or showering to wash away eggs laid overnight.
Daily changing of underwear, pyjamas, and towels for 6 weeks.
Washing bedding and nightwear at the start of treatment (hot wash where possible).
Discouraging nail biting and finger sucking.
These measures are laborious but essential. Reinfection without them is almost certain, even after treatment.
Other Worm Infections: Much Less Common in the UK
Roundworm (Ascaris lumbricoides), hookworm, and Toxocara are occasionally seen in the UK but are far less common than threadworm. They are more prevalent in tropical settings and are sometimes acquired by children who have visited high-prevalence countries. Symptoms and treatment differ by species; a GP assessment is appropriate if these infections are suspected.
Toxocariasis (from dog or cat roundworm) is occasionally transmitted via soil contaminated with animal faeces (sandpits, parks). The infection is usually mild and self-limiting but can rarely cause ocular or visceral larva migrans in children. This is a reason that dog faeces should be cleared promptly from areas where children play.
Key Takeaways
Threadworm (Enterobius vermicularis) is the most common worm infection in the UK, affecting an estimated 40% of children at some point. Infection is via ingestion of microscopic eggs transferred from the perianal area to the mouth via unwashed hands. Symptoms include intense perianal itching, particularly at night when female worms emerge to lay eggs. Treatment with mebendazole is highly effective and should be given to all household members simultaneously. The strict hygiene measures required to break the transmission cycle (daily changing of underwear, washing bedding, cutting fingernails short) are as important as medication.
