Ascariasis

Ascariasis
pyrantel pamoate[2]
Frequency	762 million (2015)[3]
Deaths	2,700 (2015)[4]

Ascariasis is a disease caused by the parasitic

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

Prevention is by improved

About 0.8 to 1.2 billion people globally have ascariasis, with the most heavily affected populations being in

Signs and symptoms

In populations where worm infections are widespread, it is common to find that most people are infected by a small number of worms, while a small number of people are heavily infected. This is characteristic of many types of worm infections.^[1][13] Those people who are infected with only a small number of worms usually have no symptoms.^[14]

Migrating larvae

As larval stages travel through the body, they may cause visceral damage,

Intestinal blockage

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.^[17] More than 796 A. lumbricoides worms weighing up to 550 g (19 oz) 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.^[18]

The worms lack teeth. However, they can rarely cause bowel perforations by inducing volvulus and closed-loop obstruction.^{[citation needed]}

Bowel obstruction

]

Allergies

Ascariasis may result in

Malnutrition

The worms in the intestine may cause malabsorption and anorexia, which contribute to malnutrition.^[22] The malabsorption may be due to a loss of brush border enzymes, erosion and flattening of the villi, and inflammation of the lamina propria.^[23]

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

Cause

• 
  The larva of Ascaris lumbricoides developing in the egg
• 
  Ascaris lumbricoides adult worms (with measuring tape for scale)
• 
  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.

Transmission

The source of infection is from objects which have been contaminated with fecal matter containing eggs.^[2] Ingestion of infective eggs from soil contaminated with human feces or contaminated vegetables and water is the primary route of infection. Infectious eggs may occur on other objects such as hands, money and furniture.^[2] Transmission from human to human by direct contact is impossible.^[25]

Transmission comes through municipal recycling of 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

The number of

] For example:

• In a study published in 1992, municipal wastewater in Riyadh, Saudi Arabia, detected over 100 eggs per litre of wastewater[27] and in Czechoslovakia was as high as 240–1050 eggs per litre.^[28]
• 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.
  helminths, particularly Ascaris, probably as a result of exposure to the raw sewage.^{[citation needed}
  ]

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 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.^[13]

Eggs can survive potentially for 15 years and a single worm may produce 200,000 eggs a day.^[2] They maintain their position by swimming against the intestinal flow.^[30]

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.^[1]

Diagnosis

Most

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 whirled appearance (bolus of worms).^{[citation needed]}

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.^[1] Handwashing with soap may be protective; however, there is no evidence it affects the severity of the disease.^[8] Eliminating the use of untreated human faeces as fertilizer is also important.^{[citation needed]}

In areas where more than 20% of the population is affected treating everyone is recommended.

Treatment

Medications

Medications that are used to kill roundworms are called

]

Piperazine is a flaccid paralyzing agent that blocks the response of Ascaris muscle to acetylcholine, which immobilizes the worm. It prevents migration when treatment is accomplished with weak drugs such as thiabendazole. If used by itself, it causes the worm to be passed out in the feces and may be used when worms have caused blockage of the intestine or the biliary duct.^[citation needed]

]

Other medications

• Hexylresorcinol effective in single dose.^[35] During the 1940s a crystoid form of this compound was the treatment of choice;^[36] patients were instructed not to chew the crystoids in order to prevent burns to the mucous membranes. A saline cathartic would be administered several hours later.^{[citation needed}
  ]
• Santonin, more toxic than hexylresorcinol^[35] and often only partly effective.^[37]
• Oil of chenopodium, more toxic than hexylresorcinol^[35]

Surgery

In some cases with severe infestation the worms may cause bowel obstruction, requiring emergency surgery.^[38] The bowel obstruction may be due to the number of worms in the bowel or twisting of the bowel.^[38] During the surgery the worms may be manually removed.^[38]

Prognosis

It is rare for infections to be life-threatening.^[1]

Epidemiology

Regions

Ascariasis is common in tropical regions as well as subtropical and regions that lack proper sanitation. It is rare to find traces of the infection in developed or urban regions.^[39]

Infection estimates

Roughly 0.8–1.3 billion individuals are infected with this intestinal worm, primarily in Africa and Asia.^[1][2][11] About 120 to 220 million of these cases are symptomatic.^[1]

Deaths

As of 2010, ascariasis caused about 2,700 directly attributable deaths, down from 3,400 in 1990.^[12] The indirectly attributable deaths due to the malnutrition link may be much higher.^{[citation needed]}

Research

There are two animal models, the mouse and pig, used in studying Ascaris infection.^[40][41]

Other animals

Ascariasis is more common in young animals than mature ones, with signs including unthriftiness, potbelly, rough hair coat, and slow growth.^[42]

In pigs, the infection is caused by Ascaris suum. It is characterized by poor weight gain, leading to financial losses for the farmer.^[1]

In horses and other equines, the equine roundworm is Parascaris equorum.^{[citation needed]}

Society and culture

Kings of England Richard III^[43] and Henry VIII^[44] both had ascariasis.

References

External links

Wikipedia's health care articles can be viewed offline with the Medical Wikipedia app.

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