Threadworms are the most common intestinal parasite in the UK, and their prevalence is something of a social secret. Around 40 per cent of children under 10 are infected at some point. They are nothing to be ashamed of, they have nothing to do with hygiene standards in the home, and they are easily treated once recognised.
The recognition part is what trips many families up. The classic symptom (perianal itching, especially at night) is often attributed to other causes, and the worms themselves, which are small and white and visible if you know to look, are not something most parents have ever seen before.
Healthbooq (healthbooq.com) covers common childhood infections and infestations, with practical guidance on recognition, treatment, and prevention.
What Threadworms Are
Enterobius vermicularis is a small parasitic worm (typically 2 to 13mm long, white, and thread-like) that lives in the large intestine. Female worms migrate to the perianal area at night to lay eggs, which causes the characteristic itching. The eggs are microscopic and can survive outside the body on surfaces and fabric for up to two weeks.
Infection occurs through the faecal-oral route: eggs deposited around the anus are transferred to the fingers by scratching, and then to the mouth directly or via surfaces and food. Young children, who put their hands in their mouths frequently and are not yet reliably washing their hands, are both more susceptible and more likely to spread infection within a household.
A child who is infected will often re-infect themselves before treatment (scratching, then touching mouth). This is called autoinfection and is the main reason that reinfection is so common without strict simultaneous hygiene measures.
Recognising Threadworms
The main symptom is perianal itching, particularly at night (because the female worms come out to lay eggs in the warmth of the sleeping child). The child may be restless at night, complain of soreness or itching around the bottom, and the area may be red from scratching.
The simplest way to confirm the diagnosis is to check with a torch at the child's perianal area about an hour or two after they have gone to sleep. Adult female worms are visible as small white threads, about 1cm long. If no worms are visible but the symptoms are present, the scotch tape test (applying clear tape to the perianal area first thing in the morning and examining it under a magnifying glass) will pick up eggs, though this is less commonly done at home.
Girls may have associated vulval itching, and occasionally worms migrate to the vagina. This is uncomfortable but not dangerous.
Treatment
Mebendazole (brand name Vermox in the UK) is the standard treatment and is available from pharmacies without prescription for children over two years. It kills the adult worms. A single dose is taken, and a second dose is given two weeks later to kill any newly hatched worms.
Crucially: all members of the household should be treated simultaneously, regardless of whether they have symptoms. Threadworm infection is often asymptomatic. Treating only the symptomatic child while others in the household remain untreated leads to reinfection.
Mebendazole is not licensed for children under two years; hygienic measures alone are recommended for this age group.
Hygiene Measures
Treatment kills worms but eggs remain viable on surfaces and fabric for up to two weeks. Without strict hygiene measures during this period, reinfection is likely regardless of treatment.
For two weeks after treatment: wash all bedding, towels, and nightclothes at 60 degrees on the day treatment is given. Vacuum bedroom carpets and soft furnishings. Clean bathroom surfaces and toilet seats. Ensure all family members wash hands thoroughly with soap and water after using the toilet and before eating. Keep fingernails short to reduce the reservoir under the nails. Try to discourage children from scratching the perianal area; loose-fitting cotton pants worn at night help reduce scratching. Shower in the morning to wash off any eggs laid during the night.
These measures feel intensive but they make the difference between treatment working and reinfection recurring.
When to See a GP
Most threadworm infections can be treated at home using pharmacy mebendazole and the hygiene measures above. See a GP if symptoms persist despite treatment and correct hygiene measures, if the child is under two years, if a pregnant woman in the household may be affected (mebendazole is not recommended in pregnancy; alternative treatment is available), or if there are any additional symptoms that seem concerning.
Key Takeaways
Threadworms (Enterobius vermicularis) are the most common worm infection in the UK, affecting primarily school-age children and their household contacts. The characteristic symptom is perianal itching, typically worse at night. Treatment with mebendazole is highly effective but requires simultaneous treatment of all household members regardless of symptoms, along with strict hygiene measures for two weeks, to prevent reinfection. Reinfection from the same household or from other children at school is the most common reason for persistent symptoms.
