Ascariasis

Ascariasis is the most common intestinal helminthic (parasitic worm) infection in humans caused by a nematode, Ascaris lumbricoides (Ascaris), that very rarely also infects the hepatobiliary system or pancreas.

The disorder stems from infectious processes.

Presentation

In the early stages of ascariasis, pulmonary symptoms including cough, dyspnea, wheezing, rales, tachypnea and urticaria and chest pain, may be observed. In certain countries, such as Saudi Arabia, the pulmonary symptoms are seasonal. Patients with an intestinal obstruction caused by Ascaris (usually children) may present with abdominal pain, distension, nausea, diarrhea, colic and anorexia. Ascariasis patients with cholangitis, pancreatitis and appendicitis (usually adults) may have nausea, vomiting, jaundice, fever and severe radiating abdominal pain [12]. If Ascaris have colonized the liver parenchyma, abscesses may occur [13]. The most common nutritional deficiencies caused by Ascaris are protein and vitamins A and C. Some prospective studies indicate a link between Ascaris-related nutritional deficiency and growth and developmental delays in children.

Workup

Patients with ascariasis will have large (50-60 µm), brown, trilayered eggs with an uneven mucopolysaccharide coat (if fertilized) in their stool, therefore, stool examination for ova and parasites should be performed. A negative stool exam may mean that patients have been infected for less than 40 days, which is the time needed for the mature Ascaris to reach the gut. Earlier in the infection cycle, during pulmonary migration, Ascaris larvae may be present in sputum which are identified microscopically in wet preparations. Also during this earlier tissue migration phase, complete blood count (CBC) will show eosinophilia but serological tests are not clinically useful for diagnosing ascariasis. During the pulmonary migration of larvae, chest radiographs may capture opacities in the lungs and during the adult phase, abdominal radiographs may reveal a swirl pattern, indicating Ascaris in the gut. Partial and complete intestinal obstruction are identified by narrow-based air fluid levels without distended bowel loops and wide-based air fluid levels with distended bowel loops, respectively, using upright plain film. If hepatobiliary infection is suspected, Ascaris in those regions can be identified with ultrasonography (real time may be used to observe worm movement) and computerized tomography (CT) scans [14] [15]. Ascaris related liver granulomata can be identified in the periportal or subcapsular regions by ill-defined, 3-35 mm nodular or wedge-shaped lesions. Along with imaging modalities endoscopic retrograde cholangiopancreatography (ERCP) can be used to diagnosis Ascaris infection, which look like long filling defects, as well as remove the worms from the biliary tract.

Treatment

Ascariasis is effectively treated with one dose of 400 mg of albendazole orally. Albendazole also kills whipworms which are commonly observed in patients with ascariasis. Pregnant women should avoid albendazole and take pyrantel pamoate instead. Pyrantel pamoate and other paralyzing agents, including piperazine and ivermectin, should not be administered in cases with intestinal obstruction as the paralyzed Ascaris may complicate surgery. An alternative to albendazole is mebendazole which is not as effective at treating whipworm infections.
A study performed in Zaire demonstrated a benefit from vitamin A supplementation in the growth and development of malnourished children with ascariasis [16]. Partial intestinal obstruction and biliary ascariasis are effectively treated through conservative means, including nothing-by-mouth (NPO) status until the obstruction resolves through normal peristalsis. A new drug, nitazoxanide, was shown to be 89% effective in treating ascariasis in Mexico offering a potential future alternative treatment [17].

Prognosis

The most common fatal complication associated with ascariasis is intestinal obstruction, which occurs in the ileum of infected children and is estimated to cause between 8,000 and 100,000 deaths per year [6]. Additionally, adult Ascaris can release toxins that induce bowel inflammation, ischemia and fibrosis. Biliary complications are more commonly observed in adults, especially those infected with other diseases such as malaria. Upon administration of albendazole, cure rates are 95% in South Africa [11], however, most patients will reacquire the disease unless they relocate or sanitation in their area significantly improves.

Etiology

Ascariasis is the most common helminthic (parasitic worm) intestinal infection in humans caused by the nematode, Ascaris, which typically resides in the jejunum and middle ileum regions of the small intestines [1].

Epidemiology

An estimated 25% of individuals worldwide (0.8-1.2 billion) are thought to be infected with Ascaris, with the majority of infected people showing no symptoms. Ascariasis is prevalent in children (2-10 years of age) who reside in developing countries and tropical regions [4] [5]. This disease is perpetuated by contamination of soil by human or animal feces and the number of incidence are highest in children who have other soil-transmitted helminthes infections, such as Trichuris trichiura and hookworm [9]. In 2005 there were an estimated 173 million cases in sub-Saharan Africa, 140 million cases in India, 86 million cases in China, 84 million cases in Latin America and the Caribbean and 23 million cases in the Middle East and North Africa. It is estimated that 60,000 deaths occur per year worldwide due to ascariasis, with most of these mortalities in children [6].

Sex distribution
Age distribution

Pathophysiology

Adult Ascaris reside in the intestines, are white or yellow and color and can grow to sizes of 15-35 cm long, making them the largest nematodes that infect humans. The life cycle of Ascaris begins in the intestines where eggs produced by females (more than 200,000 per day) may be fertilized by males. These eggs are then released by infected individuals where they will mature if conditions are favorable. According to a Chinese study, the majority of eggs released by infected individuals are fertilized with only a small percentage of unfertilized eggs being released (6-9%). Fertilized eggs may remain viable in soil for 17 months and if conditions are favorable these eggs may become infectious in 5-10 days [7]. In order for the Ascaris life cycle to proceed, fertilized eggs must make their way to the intestines, which is usually achieved through contaminated soil being ingested from hands or food. In the small intestines eggs hatch and the Ascaris larvae will pass through the intestinal wall and travel to the liver on day 4 through the portal system and reach the lungs on day 14. At this stage extreme infections can produce pneumonia but normally the larvae are expectorated and swallowed, where they will go on to the small intestines to complete their maturation into adults which takes about 65 days.

Broken down food materials in the intestines serve as the main food source for adult Ascaris. This may lead to caloric, protein or vitamin A deficiency, and subsequent growth retardation and increased susceptibility to diseases (eg. Malaria), in children with minimal diets [8]. Ascaris may cause a physical barrier, if they are large enough or become entangled with one another, leading to intestinal, common duct, pancreatic or appendiceal obstructions. The average number of adult Ascaris in infected individuals ranges from four to 16 depending on the age, geography and immunity. The maximum Ascaris lifespan is two years, therefore, those individuals with infections lasting longer than two years must have been re-exposed to contaminated soil [10].

Prevention

Appropriate sanitation and hygiene are essential for preventing ascariasis infections. At the individual level this includes thorough hand washing with soap before handling or eating food, washing, peeling and cooking all vegetables and fruits before eating and not defecating outdoors. At the community level this includes improving sanitation and providing effective sewage removal systems. Mass treatments are recommended for communities with high prevalence of ascariasis, however, this strategy only decreases morbidity but not transmission rates, therefore, emphasis should be placed on improved sanitation and hygiene practices.

Summary

Ascariasis is the most common helminthic (parasitic worm) intestinal infection in humans caused by the nematode, Ascaris [1]. Ascariasis is more common in developing countries that have inadequate sanitation whose inhabitants are suffering from poverty and overcrowding. Higher infection rates are also observed in tropical and subtropical regions. Ascaris, commonly referred to as round worm, often resides in the jejunum and ileum although the adult worm may travel to the hepatobiliary system or pancreas where it can cause cholelithiasis, acute cholecystitis, choledocholithiasis, acute pancreatitis or ascending cholangitis [2] [3].

Patient Information

Ascariasis is the most common intestinal helminthic (parasitic worm) infection in humans caused by the worm Ascaris lumbricoides (Ascaris). Ascaris infections are prevalent in developing countries with poor sanitation and areas with tropical climates. This disease is usually transmitted through food that is contaminated with Ascaris eggs, which are released in the feces of infected individuals. These eggs can survive in soil for months under the right conditions. Once Ascaris eggs are ingested they will hatch in the intestines and release larvae that migrate through blood and lymphatic vessels to the lungs. Once in the lungs, Ascaris larvae mature further and then proceed back to the intestines by way of swallowed sputum. Finally, the larvae mature in the small intestines into adults and this entire process takes 2-3 months. In the intestines mature adult Ascaris can produce and fertilize eggs that will be present in stool.

Most patients with ascariasis will not display any symptoms and if symptoms arise they are usually a result of the worms presence in the lungs or intestines. When the Ascaris larvae are traveling through the lungs, patients may experience coughing, wheezing, fever and sometimes blood in their sputum. Worms in the intestines may cause abdominal cramps and in severe cases an abundance of worms can partially or completely block the intestines. Intestinal blockage is more common in children that reside in areas with poor sanitation and can result in nausea, vomiting, abdominal swelling and pain. Intestinal blockage is the main cause of death due to complications from ascariasis.

Ascariasis is most commonly diagnosed by identifying the eggs in a patient’s stool sample. Adult worms may be identified in the intestines through ultrasonography, computed tomography (CT) and endoscopic retrograde cholangiopancreatography (ERCP). Ascariasis is effectively treated with oral administration of the prescription drugs albendazole, mebendazole or ivermectine. Pregnant women may be given alternative medications.

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References

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  9. Geissler PW, Mwaniki D, Thiong F, et al. Geophagy as a risk factor for geohelminth infections: a longitudinal study of Kenyan primary schoolchildren. Trans R Soc Trop Med Hyg. 1998; 92(1):7-11.
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  12. Louw JH. Biliary ascariasis in childhood. S Afr J Surg. 1974;12(4):219-25.
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