Ascariasis - WikiHQ

Ascariasis is a disease caused by the parasitic roundworm Ascaris lumbricoides. Infections have no symptoms in more than 85% of cases, especially if the number of worms is small.

Infection occurs by ingesting food or drink contaminated with Ascaris eggs from feces.

Prevention is by improved sanitation, which includes improving access to toilets and proper disposal of feces. Handwashing with soap appears protective. In areas where more than 20% of the population is affected, treating everyone at regular intervals is recommended. There is no vaccine. Other effective agents include tribendimidine and nitazoxanide. This makes ascariasis the most common form of soil-transmitted helminthiasis. As of 2010 it caused about 2,700 deaths a year, down from 3,400 in 1990. Another type of Ascaris infects pigs.

Migrating larvae

As larval stages travel through the body, they may cause visceral damage, peritonitis and inflammation, enlargement of the liver or spleen, and an inflammation of the lungs. Pulmonary manifestations take place during larval migration and may present as Loeffler's syndrome, a transient respiratory illness associated with blood eosinophilia and pulmonary infiltrates with radiographic shadowing.

Intestinal blockage

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

The worms can occasionally cause intestinal blockage when large numbers get tangled into a bolus or they may migrate from the small intestine, which may require surgery. More than 796 A. lumbricoides worms weighing up to were recovered at autopsy from a two-year-old South African girl. The worms had caused torsion and gangrene of the ileum, which was interpreted as the cause of death.

The worms lack teeth. However, they can rarely cause bowel perforations by inducing volvulus and closed-loop obstruction.

Bowel obstruction

Bowel obstruction may occur in up to 0.2 per 1000 per year.

Allergies

Ascariasis may result in allergies to shrimp and dustmites due to the shared antigen, tropomyosin; this has not been confirmed in the laboratory.

Malnutrition

The worms in the intestine may cause malabsorption and anorexia, which contribute to malnutrition. The malabsorption may be due to a loss of brush border enzymes, erosion and flattening of the villi, and inflammation of the lamina propria.

Others

Ascaris have an aversion to some general anesthetics and may exit the body, sometimes through the mouth, when an infected individual is put under general anesthesia.

Cause

File:Ascaris Larva.png|The larva of Ascaris lumbricoides developing in the egg

File:Ascaris lumbricoides.jpeg|Ascaris lumbricoides adult worms (with measuring tape for scale)

File:Ascaris lumbricoides adult worms.png|Ascaris lumbricoides adult worms

File:Ascaris egg, incubation process.png|Ascaris egg, incubation process: The Ascaris egg incubation process consists of placing the egg in a controlled environment, at during 28 days, in acidic conditions. This process allows for the evaluation of an egg to determine if it is viable or not.

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thumb|upright=1.3|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 feces (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.

Transmission

The source of infection is from objects contaminated with fecal matter containing eggs.

Transmission comes through municipal recycled wastewater into crop fields. This is quite common in emerging industrial economies and poses serious risks for local crop sales and exports of contaminated vegetables. A 1986 outbreak of ascariasis in Italy was traced to irresponsible wastewater recycling used to grow Balkan vegetable exports.

The number of ova (eggs) in sewage or in crops that were irrigated with raw or partially treated sewage, is a measure of the degree of ascariasis incidence. For example:

In a study published in 1992, municipal wastewater in Riyadh, Saudi Arabia, detected over 100 eggs per litre of wastewater and in Czechoslovakia was as high as 240–1050 eggs per litre.
In one field study in Marrakech, Morocco, where raw sewage is used to fertilize crop fields, Ascaris eggs were detected at the rate of 0.18 eggs/kg in potatoes, 0.27 eggs/kg in turnip, 4.63 eggs/kg in mint, 0.7 eggs/kg in carrots, and 1.64 eggs/kg in radish. A similar study in the same area showed that 73% of children working on these farms were infected with helminths, particularly Ascaris, probably as a result of exposure to the raw sewage.

Lifecycle

The first appearance of eggs in stools is 60–70 days. In larval ascariasis, symptoms occur 4–16 days after infection. The final symptoms are gastrointestinal discomfort, colic and vomiting, fever, and observation of live worms in stools. Some patients may have pulmonary symptoms or neurological disorders during the migration of the larvae. There are generally few or no symptoms. A bolus of worms may obstruct the intestine; migrating larvae may cause pneumonitis and eosinophilia. Adult worms have a lifespan of 1–2 years which means that individuals may be infected all their lives as worms die and new worms are acquired.

Eggs can survive potentially for 15 years and a single worm may produce 200,000 eggs a day.

Mechanism

Ascaris takes most of its nutrients from the partially digested host food in the intestine. There is some evidence that it can secrete enzyme inhibitors, presumably to protect itself from digestion by the hosts' enzymes. Children are often more severely affected.

The diagnosis is usually incidental when the host passes a worm in the stool or vomit. The eggs can be seen in a smear of fresh feces examined on a glass slide under a microscope and there are various techniques to concentrate them first or increase their visibility, such as the ether sedimentation method or the Kato technique. The eggs have a characteristic shape: they are oval with a thick, mamillated shell (covered with rounded mounds or lumps), measuring 35–50 micrometer in diameter and 40–70 in length. During pulmonary disease, larvae may be found in fluids aspirated from the lungs. White blood cell counts may demonstrate peripheral eosinophilia; this is common in many parasitic infections and is not specific to ascariasis. On X-ray, 15–35 cm long filling defects, sometimes with a whirled appearance (bolus of worms).

Prevention

Prevention is by improved access to sanitation which includes the use of properly functioning and clean toilets by all community members as one important aspect. For this purpose, broad-spectrum benzimidazoles such as mebendazole and albendazole are the drugs of choice recommended by WHO.

Treatment

Medications

Medications that are used to kill roundworms are called ascaricides. Those recommended by the World Health Organization for ascariasis are: albendazole, mebendazole, levamisole and pyrantel pamoate. Other effective agents include tribendimidine and nitazoxanide. During the 1940s this compound, as Crystoids brand pills, was the treatment of choice; patients were instructed not to chew the Crystoids to prevent burns to the mucous membranes. A saline cathartic would be administered several hours later.

Santonin, more toxic than hexylresorcinol
Oil of chenopodium, more toxic than hexylresorcinol

Prognosis

It is rare for infections to be life-threatening.

Infection estimates

Roughly 0.8–1.3 billion individuals are infected with this intestinal worm, primarily in Africa and Asia.

Other animals

Ascariasis is more common in young animals than mature ones, with signs including unthriftiness, potbelly, rough hair coat, and slow growth.

In pigs, the infection is caused by Ascaris suum. It is characterized by poor weight gain, leading to financial losses for the farmer. and Henry VIII both had ascariasis.

References

External links

Image (warning, very graphic):Image 1
CDC DPDx Parasitology Diagnostic Web Site