Enterobius vermicularis, also known as threadworms or pinworms, are the most common helminth infestation in the UK and usually present in children. As many as 40 per cent of young children in the UK could have suffered an infestation at some time.
1. The threadworm life cycle
The small (females about 10mm, males 4mm), white, thread-like worms can live for up to six weeks. One female can lay up to a thousand eggs, which are too small to be seen with the naked eye. The eggs can stick to fingers and fingernails from scratching, and transfer to the mouth, clothing and other surfaces. They can be easily transferred to other people if hygiene is poor.
Once one member of a household is affected the infestation will probably spread to the other occupants. Eggs may be transferred to objects, such as children's toys, worktop surfaces and kitchen equipment, and they can remain viable for as long as three weeks.
Once hatched, worms reach maturity and produce more eggs in about a fortnight. If swallowed, the eggs hatch in the intestine; if eggs around the anus hatch, they can re-enter the gut.
The most common symptom is intense irritation around the anus (and vagina in females) at night, caused by female threadworms laying eggs around the anus. It is thought the associated mucus is the irritant that causes scratching, and the irritation may be severe enough to disturb sleep. In severe infestations there may be loss of appetite and weight, and irritability from lack of sleep.
3. Making the diagnosis
The typical symptoms in a child raise the possibility of threadworm infestation, and parents may suggest the diagnosis if their family has been affected before, or if a playmate of their child has recently been diagnosed.
Sometimes a parent has already looked for worms around the anus, sheets and bed clothes, or in the stool, and may even bring an example. However, threadworms are not easy to see. Female worms are normally seen, as the smaller male worms have no need to venture forth for egg-laying.
Laboratory confirmation of an obvious infestation is not always necessary, but is useful if the diagnosis is putative or disputed. A moistened swab from the anal region or a stool sample may reveal worms or eggs. The sticky tape test may be useful: the sticky side of some clear adhesive tape is applied to the area around the anus, preferably at night, with the hope that eggs will stick to it. When the tape is sent to the laboratory, eggs will be visible under microscopy.
4. Hygiene measures
Adhering to a strict hygiene protocol alone for about six weeks can eradicate an infestation in a family without medication, but generally there is pressure to prescribe.
The hygiene measures required involve washing all sleepwear, bed linen, towels and soft toys, thorough and repeated vacuuming, repeated damp-dusting of all surfaces, keeping nails short and discouraging thumb sucking and nail biting.
Cotton gloves worn at night may prevent scratching and hand contamination. Thorough hand-washing before eating and after using the lavatory and daily washing of anal and vaginal areas are essential. Towels, flannels and toothbrushes must not be shared. Ideally, such measures should be pursued in all households whether there is infestation or not, but standards tend to slip, even after an outbreak.
Pets do not catch or pass on threadworms, but eggs can attach to fur and be ingested from fingers after an animal is stroked.
5. Medical management
OTC preparations are available for self-treatment, and this is an approach often used by parents whose children have been previously affected, without consulting their GP. Pregnant or breastfeeding women and babies under three months should not take medication - hygiene measures are the only option for these groups.
Anthelmintics, such as piperazine or mebendazole, only kill the worms, not the eggs, so good hygiene is still an essential part of management. The whole household must be treated, whether they have symptoms or not.
Piperazine paralyses the threadworms, and is combined with senna to speed up gut transmission. It is suitable for children from the age of three months, and is given as a single dose, repeated after two weeks. Patients with epilepsy or hepatic or renal impairment should not take piperazine.
Mebendazole acts by preventing the absorption of glucose, which threadworms need to survive, and is preferred for children over the age of two years. A second dose is recommended after two weeks.
Dosage of both medications depends on age and is clearly stated on accompanying literature. Side-effects are rarely troublesome with either medication, but abdominal pain or diarrhoea may occur.
Involvement outside the bowel is rare, but may occur in the vagina, uterus and abdominal cavity, and even pulmonary and hepatic involvement has been reported. One question that is frequently asked by parents is whether they can still send their children to school and the answer, with which the Health Protection Agency agrees, is yes.
- Dr Barnard is a former GP from Fareham, Hampshire