Threadworm
Exam Tips
- Classic OSCE clue: nocturnal perianal itch in a child with disturbed sleep and family members affected.
- Best confirmatory test is early-morning adhesive tape test, ideally on 3 consecutive days; stool tests are often falsely negative.
- In UK exams, management usually combines mebendazole plus strict household hygiene and treatment of contacts.
- Safety high-yield point: avoid mebendazole in pregnancy; for infants <6 months and during pregnancy/breastfeeding, prioritize prolonged hygiene-led management.
- If symptoms recur, think reinfection first (incomplete contact treatment/hygiene) before assuming drug resistance.
- For revision diagrams, review an Enterobius life-cycle figure in a standard paediatric infectious diseases textbook (egg ingestion -> intestinal maturation -> nocturnal perianal egg laying -> autoinoculation).
Definition
Threadworm (Enterobius vermicularis) is the commonest helminth infection seen in UK primary care, especially in school-aged children, and is transmitted by faeco-oral spread of microscopic eggs. The typical clinical syndrome is nocturnal perianal pruritus caused by gravid female worms migrating to lay eggs around the anus; systemic illness is unusual because infection is usually confined to the gut/perianal region.
Pathophysiology
After ingestion of infective eggs (from fingers, fomites such as bedding/toys, or occasionally inhaled dust that is then swallowed), larvae hatch in the small bowel and mature into adult worms over about 1-2 months. At night, adult females migrate to the perianal skin and deposit thousands of eggs, triggering itch and scratching; this promotes autoinoculation and household transmission. Eggs can remain viable in the environment for up to about 2 weeks, so recurrent infection is usually due to reinfection rather than drug failure. There is no obligatory extraintestinal tissue phase, which explains why severe systemic features are uncommon.
Risk Factors
- Childhood, particularly ages 4-11 years
- Household contact with an infected child
- Living in institutions or crowded settings
- Poor hand hygiene after toileting/nappy changing
- Nail biting, thumb sucking, or perianal scratching
- Exposure to contaminated bedding, nightwear, towels, toys, and bathroom surfaces
Clinical Features
Symptoms
- Intense perianal itching, classically worse at night
- Sleep disturbance, restlessness, daytime irritability, poor concentration
- Visible small white thread-like worms in stool or around anus
- Pruritus vulvae in girls/women due to genital involvement
- Occasional enuresis (bedwetting)
Signs
- Perianal excoriations from scratching
- Local secondary bacterial infection of perianal skin
- Occasionally visible motile white worms on perianal inspection (more likely at night)
- Vulval erythema/irritation if genital tract involvement
Investigations
Management
Lifestyle Modifications
- Treat as a household infection: reinforce simultaneous hygiene measures for all close contacts
- Strict handwashing with soap and warm water after toilet use/nappy changes and before food handling
- Keep fingernails short; discourage nail biting, thumb sucking, and perianal scratching
- Morning shower (including perianal cleansing) to remove eggs laid overnight
- Change underwear/nightwear and bed linen regularly after treatment; wash/dry on hot cycles
- Do not shake bedding/clothes; damp-dust and vacuum bedrooms/mattresses and clean bathrooms regularly
- No exclusion from school or nursery is required
Pharmacological Treatment
Anthelmintic
- Mebendazole 100 mg orally as a single dose (adults and children aged >=6 months); repeat 100 mg after 2 weeks if reinfection/persistent infection
Treat household contacts at the same time unless contraindicated. Contraindicated in pregnancy. In breastfeeding, only small amounts enter milk; use caution and weigh benefits/risks. Not licensed for children <2 years (specialist advice if needed). Important interactions: reduced mebendazole levels with carbamazepine, phenobarbital, phenytoin, primidone, ritonavir; increased levels with cimetidine (monitor for adverse effects). Adverse effects include abdominal pain, diarrhoea, nausea/vomiting; rare severe cutaneous reactions (SJS/TEN), angioedema, urticaria, and rare convulsions.
Complications
- Sleep loss with daytime behavioural/learning impact
- Perianal excoriation and secondary bacterial infection
- Enuresis
- Reduced appetite and weight loss
- Female genitourinary spread causing pruritus vulvae, vaginitis, and rarely salpingitis
- Rare urethritis from urethral migration
- Uncommon association with appendicitis (parasite found on histology in a small minority of appendicitis cases)
- Very rare colitis, abscess, or granuloma formation
Prognosis
Overall prognosis is excellent, but recurrence is common because eggs persist in the environment and reinfection is frequent. The life cycle is around 2 months; with coordinated household treatment and meticulous hygiene (2 weeks with mebendazole, 6 weeks if hygiene-only), symptom control and eradication are usually achieved.
Sources & References
✅NICE Guidelines(1)
- Threadworm[overview]