Ascaris lumbricoides

Ascaris lumbricoides is a nematode (roundworm) which inhabits the intestines of humans. It measures 13-35 cm in length and may live in the gut for 6-24 months. Infection is normally from food contaminated by soil containing faeces from the worm. It is prevalent in deprived areas where there is often a combination of poor sanitation and a host made vulnerable by malnutrition, iron-deficiency anaemia or impairment of growth.

Roundworm ascaris lumbricoides

© CDC, Public Domain, via Wikimedia Commons

If only a few worms are present there may be no symptoms initially; however, during the migratory phase the larvae may penetrate into the tissues and circulate around the body via the blood and lymphatic systems, commonly to the lungs. In the lungs, the larvae penetrate the pulmonary capillaries to enter the alveoli, from where they ascend into the throat and descend back into the gut where they may grow as large as 35 cm in length¹.

Épidémiologie

Incidence

• Infection with the nematode A. lumbricoides is endemic throughout the world. It is estimated that approximately 1 billion people are infected worldwide².

• The highest rates of infection with A. lumbricoides occur in China and Southeast Asia and in Africa in coastal regions of the West and in Central Africa³.

Facteurs de risque

Large numbers of A. lumbricoides eggs may be found in municipal domestic sewage and individuals eating unwashed fruit and vegetables, particularly those grown in, or near, soil fertilised with sewage are more likely to become infected. Low socio-economic class and poor sanitation are also risk factors for infection.

• Adult worms usually cause no symptoms if localised to the intestinal lumen.

• Infestation may cause impaired growth in children.

• Heavy infestations may cause abdominal pain, nausea, vomiting, anorexia, diarrhoea, malabsorption, weight loss, anal itching and intestinal obstruction.

• Migrating adult worms may cause symptomatic occlusion of the biliary tract or oral expulsion.

• Larval migration may cause cough, dyspnoea, haemoptysis and eosinophilic pneumonitis (Löffler's syndrome).

The differential diagnosis will depend on the symptoms displayed but will also include infection with Trichuris trichiura, another roundworm causing similar problems.

• Diagnosis is usually made by identifying eggs in a stool sample.

• FBC may reveal eosinophilia or anaemia.

• LFTs may reveal liver damage or low protein state.

• Specific investigations such as ultrasound, X-ray, amylase level, lung function tests and exploratory surgery may be required depending on the site of infestation.

• Endoscopic retrograde cholangiopancreatography may be useful if biliary tree involvement is suspected⁴.

• Advise the patient to wash his or her hands thoroughly after using the toilet or changing nappies and before eating or preparing food⁵.

• Traitement médicamenteux⁶:
  

  • Mebendazole is effective and generally considered to be the drug of choice for children aged 12 months and older and for adults.

  • Levamisole (unlicensed) or piperazine may be used as an alternative when mebendazole cannot be used.

• Surgical intervention may be required to treat abdominal complications⁷.

Chronic infestation with A. lumbricoides may be associated with a poor nutritional state, anaemia, failure to thrive and impaired cognition, particularly in children. Nutritional deficiencies and anaemia may be caused by heavy worm loads, especially in people in developing countries where nutritional status is often marginal⁵.

Other possible complications include:

• Intestinal: intussusception, perforation, appendicitis, peritonitis, volvulus.

• Pancreatitis, cholangitis, jaundice, liver abscesses.

• Respiratory tract obstruction.

• Uncomplicated infections respond well to treatment with anthelmintics.

• Left untreated, some infections will resolve spontaneously and adult worms usually cause little pathology if they remain in the small intestine.

• However, migration to other locations such as the liver, lungs, heart, or genitourinary tract may cause severe acute problems and death.

• Re-infections can occur rapidly after treatment and so there is a need for frequent anthelmintic drug administrations to maximise the benefit of preventative chemotherapy in developing countries⁸.

• Infection can be avoided by scrupulous attention to personal hygiene and the careful washing of all fruit and vegetables.

• Improved sanitation in developing countries is associated with a reduced risk of transmission of helminthiases to humans⁹.