Oxiúros

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.

O oxiúro macho tem cerca de 4 mm de comprimento e é raramente visto. A fêmea é maior, com 1 cm de comprimento e um pouco menos de 1 mm de diâmetro. É branca e pontiaguda em cada extremidade. Pode ser vista à noite saindo do ânus para depositar ovos. Não parece ter nenhum hospedeiro natural além dos humanos, portanto, os animais de estimação da família não são culpados. A imagem abaixo mostra duas fêmeas de oxiúros ao lado de uma régua. As marcações na régua estão a 1 mm de distância.

Oxiúros

© Erich gasboy, Public Domain, via Wikimedia Commons

Female threadworms lay an average of 11,000 tiny eggs, which are invisible to the naked eye. She lays these eggs outside the anus, or, in girls, around the vagina and urethra. Eggs are usually laid at night whilst the child sleeps. The eggs are accompanied by an irritant mucus, which causes intense pruritus and scratching. The eggs get on to the hands and from there to the mouth to re-infect.

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

A característica de apresentação é frequentemente prurido anal ou prurido vulvar, especialmente à noite. A perda de sono pode causar problemas comportamentais. Meninas que apresentam antes da puberdade corrimento vaginal, infecção do trato urinário ou enurese noturna devem ser tratadas para oxiúros.

Vermes podem ser facilmente ignorados e podem não se mover muito, parecendo simplesmente flocos de pele. Um dos pais pode ter visto algo como um pequeno pedaço de algodão branco se movendo na região anal ou vulvar, mas muitas vezes eles não são vistos e o tratamento é baseado em sintomas em vez de um diagnóstico confirmado.

• Perianal itching may be due to irritation by deodorants, tight nylon underclothes, hemorroidas ou perianal eczema. 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.

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

• In some cases 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.

No entanto, como mencionado acima, o diagnóstico não precisa ser confirmado pela visualização dos vermes, e o tratamento bem-sucedido geralmente é confirmação suficiente.

• 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.

• All the family should be treated together if possible as asymptomatic infection is common, and transmission may occur through handling of contaminated food, clothing and bed linen.

• 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.

• Children with threadworm do not need to be kept off school or nursery but good hygiene within these establishments should be encouraged.

• O tratamento com medicamentos não é recomendado para crianças com menos de 6 meses de idade. Em bebês, a atenção rigorosa às medidas de higiene mencionadas acima por seis semanas levará à morte dos vermes adultos sem que tenham a chance de reinfectar.

• 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.

• Persistent or very heavy infestation can cause loss of appetite, weight loss, insomnia, enuresis and irritability.

• 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.