Ascaris Lumbricoides

Synonym: Large roundworm, roundworm

Ascaris lumbricoides is a nematode 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.

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.¹

Incidence

Infection with the nematode Ascaris lumbricoides is endemic throughout the world. It is estimated that approximately 1 billion people are infected worldwide.² 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.³

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.

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 tests¹

• 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.
• Endoscopic retrograde cholangiopancreatography may be useful if biliary tree involvement is suspected.⁴

The drugs used against ascaris infections are known as anthelmintics. Those licensed for this use in the UK are mebendazole and piperazine. Levamisole is available on a named-patient basis.

Mebendazole⁵

Mebendazole has a cure rate of 76-95%⁶ and is used first-line in the UK as the treatment of choice for adults and children over the age of 2. In some parts of the world, where mebendazole has been used for a long period of time there are reports of reduced efficacy and possible emergence of resistance.⁷

Mebendazole is given twice a day for three days.

• Mode of Action: It acts on the secretory mechanism of individual cells in the intestinal tract, blocking glucose uptake.^1,8
• Contraindications: Very little is absorbed systemically, so contraindications are few. The manufacturers recommend avoiding in pregnancy due to teratogenicity in animal studies. Studies of exposure in pregnant women however have failed to demonstrate any significant teratogenic tendency.⁹ The manufacturers also advise avoiding use in lactation, although the amount excreted in breast milk is thought to be very small.⁵
• Initiation of Treatment: If the patient has a history of liver disease, liver function tests should be arranged. Ensure also that the patient has not had a previous reaction to the medicine, is not pregnant and is not breastfeeding.
• Complications and reasons to discontinue drug: The commonest reasons for intolerance are gastrointestinal symptoms (nausea, vomiting, abdominal pain and diarrhoea) and central nervous system symptoms (headache and dizziness). Alopecia can occur, but is rare at the dosages used for roundworm infection. Other rare adverse effects may include agranulocytosis, angio-oedema and seizures.¹

Piperazine

Piperazine is used for children aged between 3 months and 2 years. It can also be used as alternative for adults. It is given as a single dose and is therefore particularly good where compliance is an issue. It is often combined with senna to ensure complete expulsion.¹⁰ It has been used with some success in ascariatic intestinal obstruction. In biliary ascariasis it can be instilled into the bile duct via an endoscope.¹¹ However, providing endoscopy is not required for diagnosis (most cases are diagnosed by identification of eggs) the oral route is to be preferred, as it is inexpensive and safer.⁴

• Mode of Action: Piperazine acts as an agonist on nematode muscle GABA receptors, effectively paralysing the worm.^12,13
• Contraindications: Piperazine can cause neurotoxic reactions resulting in convulsions in people with severe renal disease and epilepsy and is therefore contraindicated in these conditions and in neurological disease in general.¹⁰ It can also cause a hepatitis-like syndrome and should be avoided in severe hepatic disease.¹⁴
  
  The manufacturers advise avoidance of piperazine in pregnancy, especially in the first trimester,¹⁰ although the risk appears to be theoretical rather than real. Piperazine is also excreted in only a small quantity in breast milk, although the manufacturers advise avoiding in lactation. The senna with which it is sometimes combined can also cause colic in infants and if this combination has to be used the mother should breastfeed prior to taking the medication.
• Complications and reasons to discontinue drug: The commonest side effects are gastrointestinal, mainly nausea, vomiting and diarrhoea. Allergic reactions such as angioneurotic oedema and bronchospasm occasionally occur. Rarely, neurotoxic reactions cause cerebellar ataxia, clumsiness and gait abnormalities ('worm wobble') but this is usually against a background in which high blood levels are achieved - e.g. high dosage regimes or renal insufficiency.¹⁵

Levamisole

It is highly effective and it is given as a single dose. As it is does not have a UK license it tends to be used on a named-patient basis where the other drugs fail,¹⁰ usually under specialist guidance:

• Mode of action: Levamisole is a nicotinic acid antagonist which also acts on muscles, at the membrane receptor level.¹²
• Contraindications: The only absolute contraindications are known hypersensitivity or allergy to the drug. Unlike mebendazole and piperazine, levamisole is not listed in the British National Formulary as a drug which should be avoided in pregnancy. There is a significant evidence base to suggest minimal or no toxic effects on the fetus.¹⁶
• Initiation of treatment: Levamisole is not licensed for this indication, so the responsibility for any adverse effects rest solely with the prescriber. It is recommended in this situation for GPs to seek the advice of a consultant colleague before prescribing.
• Complications and reasons to discontinue drug: Levamisole causes less side effects than piperazine.¹⁷ When they do occur, the adverse effects are mainly headaches and abdominal pain.¹⁸

There are no particular monitoring requirements for any of these drugs, as it is unlikely they will be required for any length of time for this indication.

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.