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Ascariasis

Ascariasis is a disease caused by the parasitic roundworm Ascaris lumbricoides. It is the most common form of soil-transmitted helminthiasis, affecting around 0.8 to 1.2 billion people globally, primarily in sub-Saharan Africa, Latin America, and Asia.

Infection is often asymptomatic, particularly in cases with a low worm burden. However, symptomatic cases may present with respiratory and gastrointestinal symptoms. The disease is transmitted through ingestion of Ascaris eggs from contaminated food, water, or soil.

High number of ascaris worms – visible as black tangled mass – are filling the duodenum, the first portion of the bowel after the stomach, of this South African patient (X-ray image with barium as contrast medium).
High number of ascaris worms – visible as black tangled mass – are filling the duodenum, the first portion of the bowel after the stomach, of this South African patient (X-ray image with barium as contrast medium).

Signs and Symptoms

In populations with widespread worm infections, most people are infected by a small number of worms and usually have no symptoms. However, a small number of people may be heavily infected and symptomatic.

Migrating Larvae

Larval stages travelling through the body can cause visceral damage, peritonitis, liver or spleen enlargement, and lung inflammation. Pulmonary manifestations may present as Loeffler's syndrome, a transient respiratory illness associated with blood eosinophilia and pulmonary infiltrates.

Intestinal Blockage

In severe cases, worms can cause intestinal blockage, as seen in the X-ray of a South African patient. This may require surgical intervention. In some cases, worms may cause torsion and gangrene of the ileum.

Piece of intestine, blocked by worms, surgically removed from a three-year-old boy in South Africa
Piece of intestine, blocked by worms, surgically removed from a three-year-old boy in South Africa

Bowel Obstruction

Bowel obstruction may occur, with worms sometimes blocking the ampulla of Vater or entering the biliary tree, causing acute pancreatitis, cholangitis, or cholecystitis.

Allergies and Malnutrition

Ascariasis may result in allergies to shrimp and dust mites due to shared antigens. It can also cause malnutrition through malabsorption and anorexia.

Other Symptoms

Ascaris worms may exit the body through the mouth when an infected person is under general anaesthesia.

Cause

Infection occurs through ingestion of Ascaris eggs from contaminated food, water, or soil. The eggs hatch in the intestines, and larvae migrate through the body, eventually reaching the lungs and then returning to the intestines to mature into adult worms.

The larva of Ascaris lumbricoides developing in the egg
The larva of Ascaris lumbricoides developing in the egg
Ascaris lumbricoides adult worms (with measuring tape for scale)
Ascaris lumbricoides adult worms (with measuring tape for scale)
Ascaris lumbricoides adult worms
Ascaris lumbricoides adult worms
Ascaris egg, incubation process: The Ascaris egg incubation process consists of placing the egg in a controlled environment, at 26°C (79°F) during 28 days, in acidic conditions. This process allows for the evaluation of an egg to determine if it is viable or not.
Ascaris egg, incubation process: The Ascaris egg incubation process consists of placing the egg in a controlled environment, at 26°C (79°F) during 28 days, in acidic conditions. This process allows for the evaluation of an egg to determine if it is viable or not.
Ascaris life cycle: Adult worms (1) live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with faeces (2). Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks (3), depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed (4), the larvae hatch (5), invade the intestinal mucosa, and are carried via the portal, then systemic circulation and/or lymphatics to the lungs. The larvae mature further in the lungs (6) (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed (7). Upon reaching the small intestine, they develop into adult worms (8). Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years.
Ascaris life cycle: Adult worms (1) live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with faeces (2). Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks (3), depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed (4), the larvae hatch (5), invade the intestinal mucosa, and are carried via the portal, then systemic circulation and/or lymphatics to the lungs. The larvae mature further in the lungs (6) (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed (7). Upon reaching the small intestine, they develop into adult worms (8). Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years.

Diagnosis

Diagnosis is typically made by identifying Ascaris eggs or worms in faeces. The eggs have a characteristic oval shape with a thick, mamillated shell and can be seen under a microscope. During pulmonary disease, larvae may be found in fluids aspirated from the lungs. Radiographic imaging may show long filling defects or a whirled appearance of a bolus of worms.

Prevention

Prevention involves improved sanitation, including the use of clean toilets and proper disposal of faeces. Handwashing with soap is also protective. In areas where more than 20% of the population is affected, mass drug administration (MDA) is recommended, typically involving medications such as albendazole or mebendazole.

Treatment

Medications

Ascaricides recommended by the World Health Organisation include albendazole, mebendazole, levamisole, and pyrantel pamoate. These medications are effective in removing parasites and eggs from the intestines. Other effective agents include tribendimidine and nitazoxanide.

Surgery

In severe cases with bowel obstruction, emergency surgery may be required to manually remove the worms.

Epidemiology

Ascariasis is common in tropical and subtropical regions and is rare in developed or urban areas. The disease causes about 2,700 deaths annually, primarily among children in affected regions.

Ascariasis deaths per million persons in 2012
Ascariasis deaths per million persons in 2012
Disability-adjusted life year for ascariasis per 100,000 inhabitants in 2004
Disability-adjusted life year for ascariasis per 100,000 inhabitants in 2004

Research and Other Animals

Animal models, including mice and pigs, are used to study Ascaris infection. Ascariasis also affects pigs (Ascaris suum) and horses (Parascaris equorum), causing poor weight gain and financial losses for farmers.


Self-assessment MCQs (single best answer)

What is the causative agent of Ascariasis?



In which regions is Ascariasis most commonly found?



What is the primary mode of transmission for Ascariasis?



Which of the following symptoms is associated with migrating larvae of Ascaris lumbricoides?



What complication may arise from a severe case of Ascariasis?



Which syndrome is associated with the pulmonary manifestations of Ascariasis?



How is Ascariasis typically diagnosed?



What is a recommended medication for treating Ascariasis according to the World Health Organisation?



In what scenario might surgery be required for a patient with Ascariasis?



Which of the following is a preventive measure for Ascariasis?



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