Ascariasis
Template:Short description Template:About Template:Distinguish Template:Infobox medical condition (new) Ascariasis is a disease caused by the parasitic roundworm Ascaris lumbricoides.<ref name=Dold2011 /> Infections have no symptoms in more than 85% of cases, especially if the number of worms is small.<ref name=Dold2011>Template:Cite journal</ref> Symptoms increase with the number of worms present and may include shortness of breath and fever at the beginning of the disease.<ref name=Dold2011 /> These may be followed by symptoms of abdominal swelling, abdominal pain, and diarrhea.<ref name=Dold2011 /> Children are most commonly affected, and in this age group the infection may also cause poor weight gain, malnutrition, and learning problems.<ref name=Dold2011 /><ref name=Hagel2010 /><ref name=WHO2013>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Infection occurs by ingesting food or drink contaminated with Ascaris eggs from feces.<ref name=Hagel2010 /> The eggs hatch in the intestines, the larvae burrow through the gut wall, and migrate to the lungs via the blood.<ref name=Hagel2010 /> There they break into the alveoli and pass up the trachea, where they are coughed up and may be swallowed.<ref name=Hagel2010 /> The larvae then pass through the stomach a second time into the intestine, where they become adult worms.<ref name=Hagel2010 /> It is a type of soil-transmitted helminthiasis and part of a group of diseases called helminthiases.<ref name=NTD2017>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Prevention is by improved sanitation, which includes improving access to toilets and proper disposal of feces.<ref name=Dold2011 /><ref>Template:Cite journal</ref> Handwashing with soap appears protective.<ref name=Fung2009>Template:Cite journal</ref> In areas where more than 20% of the population is affected, treating everyone at regular intervals is recommended.<ref name=Dold2011 /> Reoccurring infections are common.<ref name=Hagel2010 /><ref>Template:Cite journal</ref> There is no vaccine.<ref name=Hagel2010 /> Treatments recommended by the World Health Organization are the medications albendazole, mebendazole, levamisole, or pyrantel pamoate.<ref name=Hagel2010>Template:Cite journal</ref> Other effective agents include tribendimidine and nitazoxanide.<ref name=Hagel2010 />
About 0.8 to 1.2 billion people globally have ascariasis, with the most heavily affected populations being in sub-Saharan Africa, Latin America, and Asia.<ref name=Dold2011 /><ref name=Kei2010 /><ref name=Fen2012>Template:Cite journal</ref> This makes ascariasis the most common form of soil-transmitted helminthiasis.<ref name=Kei2010>Template:Cite journal</ref> As of 2010 it caused about 2,700 deaths a year, down from 3,400 in 1990.<ref name=Loz2012>Template:Cite journal</ref> Another type of Ascaris infects pigs.<ref name=Dold2011 /> Ascariasis is classified as a neglected tropical disease.<ref name=NTD2017/> Template:TOC limit
Signs and symptomsEdit
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.<ref name="Dold2011" /><ref name="Anderson1" /> Those people who are infected with only a small number of worms usually have no symptoms.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Migrating larvaeEdit
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.<ref>Torok E. Oxford Handbook Infect Dis and Microbiol, 2009</ref>
Intestinal blockageEdit
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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.<ref>Template:Cite journal</ref> More than 796 A. lumbricoides worms weighing up to Template:Convert 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.<ref>Template:Cite journal</ref>
The worms lack teeth. However, they can rarely cause bowel perforations by inducing volvulus and closed-loop obstruction.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Bowel obstructionEdit
Bowel obstruction may occur in up to 0.2 per 1000 per year.<ref name="Dold2011" /> A worm may block the ampulla of Vater, or go into the main pancreatic duct, resulting in acute pancreatitis with raised serum levels of amylase and lipase. Occasionally, a worm can travel through the biliary tree and even into the gallbladder, causing acute cholangitis or acute cholecystitis.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>Template:Citation needed
AllergiesEdit
Ascariasis may result in allergies to shrimp and dustmites due to the shared antigen, tropomyosin; this has not been confirmed in the laboratory.<ref name="Berman2012">Template:Citation</ref><ref name="pmid18486690">Template:Cite journal</ref>
MalnutritionEdit
The worms in the intestine may cause malabsorption and anorexia, which contribute to malnutrition.<ref name="Hall2">Template:Cite journal</ref> The malabsorption may be due to a loss of brush border enzymes, erosion and flattening of the villi, and inflammation of the lamina propria.<ref name="Stephenson1">Template:Cite book</ref>
OthersEdit
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.<ref>Template:Cite journal</ref>
CauseEdit
- Ascaris Larva.png
The larva of Ascaris lumbricoides developing in the egg
- Ascaris lumbricoides.jpeg
Ascaris lumbricoides adult worms (with measuring tape for scale)
- Ascaris lumbricoides adult worms.png
Ascaris lumbricoides adult worms
- Ascaris egg, incubation process.png
Ascaris egg, incubation process: The Ascaris egg incubation process consists of placing the egg in a controlled environment, at Template:Convert during 28 days, in acidic conditions. This process allows for the evaluation of an egg to determine if it is viable or not.
TransmissionEdit
The source of infection is from objects contaminated with fecal matter containing eggs.<ref name=Hagel2010 /> 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 objects such as hands, money, and furniture.<ref name=Hagel2010 /> Transmission from human to human by direct contact is impossible.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
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.<ref>Template:Cite book</ref>
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.Template:Citation needed For example:
- In a study published in 1992, municipal wastewater in Riyadh, Saudi Arabia, detected over 100 eggs per litre of wastewater<ref>Template:Cite journal</ref> and in Czechoslovakia was as high as 240–1050 eggs per litre.<ref>Template:Cite journal</ref>
- 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.<ref>Template:Cite journal</ref> 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.Template:Citation needed
LifecycleEdit
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.<ref name=Anderson1>Template:Cite book</ref>
Eggs can survive potentially for 15 years and a single worm may produce 200,000 eggs a day.<ref name=Hagel2010 /> They maintain their position by swimming against the intestinal flow.<ref name=Crompton1>Template:Cite book</ref>
MechanismEdit
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.<ref name=Dold2011 />
DiagnosisEdit
Most diagnoses are made by identifying the appearance of the worm or eggs in feces. Due to the large quantity of eggs laid, diagnosis can generally be made using only one or two fecal smears.<ref>Template:Cite book</ref> 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).Template:Citation needed
PreventionEdit
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.<ref name=Dold2011 /> Handwashing with soap may be protective; however, there is no evidence it affects the severity of the disease.<ref name=Fung2009 /> Eliminating the use of untreated human faeces as fertilizer is also important.Template:Citation needed
In areas where more than 20% of the population is affected treating everyone is recommended.<ref name=Dold2011 /> This has a cost of about 2 to 3 cents per person per treatment.<ref name=Dold2011 /> This is known as mass drug administration and is often carried out among school-age children.<ref>Template:Cite journal</ref> For this purpose, broad-spectrum benzimidazoles such as mebendazole and albendazole are the drugs of choice recommended by WHO.<ref>Template:Cite book</ref>
TreatmentEdit
MedicationsEdit
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.<ref name=Hagel2010 /> Single-dose of albendazole, mebendazole, and ivermectin are effective against ascariasis. They are effective at removing parasites and eggs from the intestines.<ref>Template:Cite journal</ref> Other effective agents include tribendimidine and nitazoxanide.<ref name=Hagel2010 /> Pyrantel pamoate may induce intestinal obstruction in a heavy worm load. Albendazole is contraindicated during pregnancy and children under two years of age. Thiabendazole may cause migration of the worm into the esophagus, so it is usually combined with piperazine.Template:Citation needed
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.Template:Citation needed
Corticosteroids can treat some of the symptoms, such as inflammation.Template:Cn
Other medicationsEdit
- Hexylresorcinol, effective in a single dose.<ref name="Holt11th">Holt, Jr Emmett L, McIntosh Rustin: Holt's Diseases of Infancy and Childhood: A Textbook for the Use of Students and Practitioners. Appleton and Co, New York, 11th edition</ref> 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.<ref>Template:Cite report</ref>
- Santonin, more toxic than hexylresorcinol<ref name="Holt11th" /> and often only partly effective.<ref>Template:Cite book</ref>
- Oil of chenopodium, more toxic than hexylresorcinol<ref name="Holt11th" />
SurgeryEdit
In some cases with severe infestation, the worms may cause bowel obstruction, requiring emergency surgery.<ref name=Hef2009 /> The bowel obstruction may be due to the number of worms in the bowel or twisting of the bowel.<ref name=Hef2009 /> During the surgery the worms may be manually removed.<ref name=Hef2009>Template:Cite journal</ref>
PrognosisEdit
It is rare for infections to be life-threatening.<ref name=Dold2011 />
EpidemiologyEdit
RegionsEdit
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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Infection estimatesEdit
Roughly 0.8–1.3 billion individuals are infected with this intestinal worm, primarily in Africa and Asia.<ref name="Dold2011" /><ref name="Hagel2010" /><ref name="Fen2012" /> About 120 to 220 million of these cases are symptomatic.<ref name="Dold2011" />
DeathsEdit
As of 2010, ascariasis caused about 2,700 directly attributable deaths, down from 3,400 in 1990.<ref name="Loz2012" /> The indirectly attributable deaths due to the malnutrition link may be much higher.Template:Cn
ResearchEdit
Mouse and pig animal models are used to study Ascaris infection.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
Other animalsEdit
Ascariasis is more common in young animals than mature ones, with signs including unthriftiness, potbelly, rough hair coat, and slow growth.<ref name="eXtension2">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
In pigs, the infection is caused by Ascaris suum. It is characterized by poor weight gain, leading to financial losses for the farmer.<ref name="Dold2011" />
In horses and other equines, the equine roundworm is Parascaris equorum.Template:Cn Template:Clear right
Society and cultureEdit
Kings of England Richard III<ref>Template:Cite journal</ref> and Henry VIII<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> both had ascariasis.
ReferencesEdit
External linksEdit
- Image (warning, very graphic):Image 1
- CDC DPDx Parasitology Diagnostic Web Site
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