Ossiuri

What are threadworms?

Threadworms are a very common nematode which infect the large intestine. These infections occurs throughout the world. They are also known as pinworms (in most of the world, the UK, Australia and New Zealand being the exceptions) or enterobiasis, as the Latin name for threadworms is Enterobius vermicularis.

The male threadworm is about 4 mm long and is rarely seen. The female is bigger at 1 cm long and a little under 1 mm in diameter. It is white and pointed at each end. It may be seen at night emerging from the anus to lay eggs. It does not appear to have any natural host other than humans and so family pets are not to blame. The image below shows two female pinworms next to a ruler. The markings on the ruler are 1 mm apart.

Ossiuri

© Erich gasboy, Public Domain, via Wikimedia Commons

Le femmine degli ossiuri depongono in media 11.000 minuscole uova, che sono invisibili a occhio nudo. Depongono queste uova all'esterno dell'ano o, nelle bambine, intorno alla vagina e all'uretra. Le uova vengono solitamente deposte di notte mentre il bambino dorme. Le uova sono accompagnate da un muco irritante, che provoca intenso prurito e graffi. Le uova finiscono sulle mani e da lì alla bocca per reinfettare.

Eggs are swallowed and exposed to digestive juices in the upper intestinal tract. Infection or re-infection can occur by directly swallowing, or by inhaling and then swallowing, the eggs. Occasionally, infection may occur when the eggs hatch on the mucosa and the larvae migrate back up the rectum.

Following ingestion of the eggs, the larvae hatch in the small intestine and establish themselves in the colon, reaching maturity in approximately two weeks. Adult worms live for up to six weeks.

This is the most common helminthic infection in the UK. An average GP practice of 10,000 patients would expect about 40 consultations a year for threadworms but many more simply buy medication from a pharmacist. It tends to affect family groups or institutions.

Prevalence is highest between the ages of 5 and 9 years but all ages may be affected. Studies in asymptomatic children suggest that between 18 and 34% of children have threadworms.¹

The presenting feature is often pruritus ani or pruritus vulvae, especially at night. Loss of sleep can cause behavioural problems. Girls presenting before puberty with vaginal discharge, urinary tract infection, or nocturnal enuresis should be treated for threadworm.

I vermi possono essere facilmente trascurati e potrebbero non muoversi molto, semplicemente sembrando scaglie di pelle. Un genitore potrebbe aver visto qualcosa come un minuscolo pezzo di cotone bianco muoversi nella regione anale o vulvare, ma spesso non vengono visti e il trattamento si basa sui sintomi piuttosto che su una diagnosi confermata.

• Perianal itching may be due to irritation by deodorants, tight nylon underclothes, emorroidi oppure eczema perianale. Deodorants and haemorrhoids are rather more a problem of adults than of children.

• A number of skin diseases may cause pruritus. Psoriasis is said not to itch but it may in the anogenital region.

• Neurotic excoriation.

• Vulvovaginite is very common in young girls and can cause itching as well as soreness.

• In alcuni casi the possibility of sexual abuse must be considered - if there is a suspicion of sexual abuse then immediate referral to a paediatrician is essential.

Often the diagnosis is clear and no investigation is required. There is no need to see the threads and treatment can be given on the basis of symptoms.

If parents want to confirm the presence of threadworms then they can use the adhesive tape test for eggs. Transparent wide hypo-allergenic adhesive tape is applied to the perianal skin first thing in the morning, before wiping or bathing. It does not have to be left on overnight. Many tiny eggs are usually seen adherent to the tape although they are so small they can be difficult to detect.

Another test is to apply some thick cream such as Sudocrem over the anus and vulva before bed. If tight underwear is worn all night then worms can often be seen in the cream on the underwear the next morning.

However, as above, the diagnosis does not need to be confirmed by seeing the worms, and successful treatment is often confirmation enough.

• Mebendazole is the drug of choice in adults and in children older than 2 years. It is given as a single oral dose, and is best repeated after two to three weeks in case re-infection has occurred. Mebendazole kills the worms.¹

• This can be bought over the counter but can also be prescribed.

• Other possible drugs include albendazole and pyrantel pamoate.

• Tutta la famiglia dovrebbe essere trattata insieme, se possibile, poiché l'infezione asintomatica è comune e la trasmissione può avvenire attraverso la manipolazione di cibo, abbigliamento e biancheria da letto contaminati.

• The drugs do not harm threadworm eggs, which may remain viable for up to two weeks. To avoid re-infection it is important to clear the environment of viable worm eggs on the day that drug treatment is started.

• Hygiene measures include:

  • Wear tight underwear at night.

  • Have a bath or shower each morning and wash around the anus.

  • Change and wash underwear, nightwear and, if feasible, bed linen and towels each day for the week after treatment. Do not shake them as this spreads eggs. Do not share towels.

  • Keep fingernails short and clean. Wash hands and scrub under the nails first thing in the morning, after using the toilet or changing nappies, and before eating or preparing food.

• I bambini con ossiuri non devono essere tenuti lontani da scuola o asilo, ma una buona igiene all'interno di questi istituti dovrebbe essere incoraggiata.

• Drug treatment is not recommended for children under the age of 6 months. In babies, scrupulous attention to the above hygiene measures for six weeks will lead to the adult worms dying without having had the chance to re-infect.

• Mebendazole can be used in pregnancy or breastfeeding but the hygiene advice for babies is also true for women who want to avoid medication. ⁴

• Scratching of the perianal skin may cause inflammation, laceration and secondary infection.

• Un'infestazione persistente o molto grave può causare perdita di appetito, perdita di peso, insonnia, enuresi e irritabilità.

• Ectopic lesions means infestation outside the alimentary tract. Very occasionally worms are found in the ears and nose. Rarely, worms invade the abdominal cavity, causing granulomas of the liver, ovary, kidney, spleen and lung. Chronic pelvic peritonitis and ileocolitis have been described.

Re-infection is common.

Prevention relies on good hygiene, especially washing of hands before eating or preparing food. Sucking fingers or biting nails is to be discouraged. Treatment is very effective and it should be repeated to assure complete eradication.