Ascaris Lumbricoides

Synonym: Large round worm

Incidence

Infection with the nematode Ascaris lumbricoides is endemic throughout the world. It is estimated that approximately 1 billion people are infected worldwide.¹ The highest rates of Ascaris infection occur in China and Southeast Asia, and in Africa in coastal regions of the West and in Central Africa.²

Risk Factors

Large numbers of Ascaris 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.

Ascaris lumbricoides is a nematode, or round worm, which is responsible for considerable morbidity throughout the world. Spread of the parasite takes place by ingestion of the eggs via the faecal/oral route. If only a few worms are present there may be no symptoms initially, but 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 30cms in length.³

Symptoms

The symptoms and signs caused by the infection will depend on the stage of development and the site of the parasite.

Larval migration into the lungs can lead to a pneumonitis producing:

• Wheeze
• Cough
• Chest pain
• Shortness of breath

Larval migration elsewhere may cause:

• Conjunctivitis
• Fever
• Convulsions
• Skin rash

The presence of mature worms may cause:

• Abdominal pain
• Colic
• Nausea
• Vomiting
• Anorexia
• Anal itching
• Weight loss
• Diarrhoea
• Malabsorption

Signs

The signs and complications of the infection are also dependent on the developmental stage of the Ascaris, and the number of mature worms present.

Signs caused by the larval stage:

• Asthma
• Eosinophilia
• Rash
• Conjunctivitis

Caused by the mature worms:

• Abdominal distension
• Intestinal obstruction
• Intestinal intussusception
• Intestinal perforation
• Appendicitis
• Peritonitis
• Pancreatitis
• Volvulus
• Cholangitis
• Jaundice
• Liver abscesses
• Respiratory tract obstruction

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

Laboratory Tests⁴

• Diagnosis is usually made by finding eggs in a faeces sample, although occasionally it may be made by finding mature worms in the faeces, throat or even nose of an individual.
• Full blood count may reveal eosinophilia or anaemia.
• Liver function tests 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.

Drugs^3,5,6

Treatment is usually with anti-helmintic agents such as:

• Levamisole
• Mebendazole⁷
• Piperazine⁸

See also: Ascaris Lumbricoides Management.

Surgical intervention may be required to treat abdominal complications.

Chronic infestation with Ascaris is often associated with a poor nutritional state, anaemia, failure to thrive and impaired cognition , particularly in children.

Uncomplicated infections respond well to treatment with anti-helmintics. Left untreated, some infections will resolve spontaneously, but many will go on to produce complications, malnutrition or even death.

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