Ascaris lumbricoides

Description, Causes and Risk Factors:

A large roundworm of humans, one of the commonest human parasites (8-12 inches in length); various symptoms such as restlessness, fever, and sometimes diarrhea are attributed to its presence, but usually it causes no definite symptoms; the similar species, Ascaris suum (or Ascaris lumbricoides suum) is very common in swine, but is not readily transmitted to humans, and vice versa; the types are morphologically and immunologically similar but apparently are host-adapted types, considered distinct species or races.

Adult A. lumbricoides live in the lumen of the small intestine. A female may produce 200,000 eggs each day, which are passed with the feces of the host. Ingested unfertilized eggs are not infective, but fertile eggs begin to develop and become infective after 18 days to several weeks, depending on environmental conditions (an optimal environment being moist, warm, shaded soil). After infective eggs are swallowed, the larvae hatch, invade the intestinal mucosa, and are carried via first the portal and then the systemic circulation to the lungs. The larvae mature further in the lungs for 10 to 14 days, then penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed. Upon reaching the small intestine, they develop into adult worms. Between two and three months are required from ingestion of the infective eggs to oviposition (egg-laying) of the adult female. Adult worms can live one to two years.

Poor sanitation is usually the most important risk factor for infection, and women are more affected because progesterone plays a role in inducing Oddi's sphincter relaxation, allowing the nematode to access the biliary duct. Although not common in developed countries, ascaris lumbricoides infection is increasingly likely to be encountered by clinicians because of the growing rates of travel to developing countries and increased migration.

Ascaris lumbricoides has a worldwide distribution, but is most prevalent in tropical and subtropical regions and areas with inadequate sanitation. In the United States, it occurs in rural regions of the southeastern U.S. The exact prevalence is unknown.

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 maximize the benefit of preventive chemotherapy in developing countries.

Infection can be avoided by scrupulous attention to personal hygiene and the careful washing of all fruits and vegetables before eating. Improved sanitation facility is very essential in controlling and preventing the disease.

Eggs of A. lumbricoides have been identified in archeological coprolites in the States, Europe, Africa, the Middle East, and New Zealand, the oldest ones being more than 24,000 years old.

Symptoms:

People infected with multiple worms experience diarrhea, abdominal pain, general malaise and weakness. These symptoms can affect people's ability to work and learn, and can impair physical growth.

Diagnosis:

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

• FBC may reveal eosinophilia or anemia.

• 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 suspected.

Treatment:

Ascaris lumbricoides is usually treated for 1-3 days with medicine prescribed by your Parasitology. Some common drugs are albendazole, ivermectin, nitazoxanide and mebendazole (Vermox™), which kills roundworms by preventing them from absorbing nutrients. You may be asked to provide additional stool samples 1-2 weeks after the treatment to confirm that the worms are dead.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.