AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Multimedia
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Multimedia
• References

Background

Ascariasis is the most common helminthic infection, with an estimated worldwide prevalence of 25% (0.8-1.4 billion people). Usually asymptomatic, infections are most prevalent in children of tropical and developing countries, where they are perpetuated by contamination of soil by human feces or use of untreated feces as fertilizer. Symptomatic disease may be manifested by growth retardation, pneumonitis, intestinal obstruction, or hepatobiliary and pancreatic injury. In developing countries, ascariasis may exist as a zoonotic infection associated with exposure to pigs or pig manure.

Pathophysiology

Ascaris lumbricoides is the largest of the common nematode (roundworm) infections of man. The white or yellow adult is 15-35 cm long and lives 10-24 months in the jejunum and middle ileum of the intestine. Each female produces 240,000 eggs per day, which are fertilized by nearby male worms. A recent study from China showed that 45% of infected persons shed only fertilized eggs, 40% shed fertilized and unfertilized eggs, and 20% shed only unfertilized eggs. Unfertilized eggs accounted for only 6-9% of eggs shed. Fertilized eggs released into favorable soil may become infectious within 5-10 days. Eggs may remain viable in soil for up to 17 months. Infection occurs through soil contamination of hands or food, ingestion, and the subsequent hatching of eggs in the small intestine.

Second-stage larvae pass through the intestinal wall and migrate through the portal system to the liver (4 d) and then the lungs (14 d). A large exposure may produce subsequent pneumonia and eosinophilia. Symptoms of pneumonitis include wheezing, dyspnea, nonproductive cough, hemoptysis, and fever. Larvae are expectorated and swallowed, eventually reaching the jejunum, where 65 days are needed for maturation to adults.

Adult worms feed on digestion products of the host. Children with marginal diet may be susceptible to protein, caloric, or vitamin A deficiency, resulting in retarded growth and increased susceptibility to infectious diseases such as malaria. Intestinal (usually ileal), common duct, pancreatic, or appendiceal obstruction may occur from the large and tangled worms. Mean worm burden varies from more than 16 to 4 and appears related to host factors, particularly age, geophagy, and immunity. Worms do not multiply in the host. For infection to be maintained beyond the 2-year maximum lifespan, re-exposure must occur.

Ascaris lumbricoides suum, a swine nematode, may be responsible for zoonotic infection. Distinguishing this worm from A lumbricoides is difficult. A suum appears to be the predominant infection in well-developed countries with excellent sanitation. In this setting, such as Denmark or the United States, children have low worm burden and may present with only acute eosinophilia or eosinophilic liver lesions that are seen on CT scan.

Frequency

United States

In 1974, an estimated 4 million people, mainly in the Southeast, were infected. Immigrants from countries with high prevalence comprise most recent cases. A suum infection probably represents most cases of ascariasis acquired in the United States because of exposure to pigs or pig manure.

International

The prevalence of ascariasis is highest in children aged 2-10 years, with the highest intensity of infection occurring in children aged 5-15 years who have simultaneous infections with other helminths such as Trichuris trichiura and hookworm. The Centers for Disease Control and Prevention (CDC) estimated that the prevalence in 2005 was 86 million cases in China, 204 million elsewhere in East Asia and the Pacific, 173 million in sub-Saharan Africa, 140 million in India, 97 million elsewhere in South Asia, 84 million in Latin America and the Caribbean, and 23 million in the Middle East and North Africa.

Because the lifespan of the adult worm in the intestine is only one year, this prevalence of infection must be maintained by frequent re-exposure and reinfection over the lifetime of the person. Frequency and intensity of infection remain high throughout life in endemic areas and pose a risk to both elderly and young persons. Estimates of disability-adjusted years of life due to ascariasis have fallen because of development and management programs during the 1990's, especially in Asia, but still constitute a significant burden in some countries.

Mortality/Morbidity

• Children have the highest rates of prevalence and intensity and are more likely than adults to be symptomatic. In children, intestinal obstruction caused by heavy worm burden (60 or more) is the most common manifestation of disease. Among children aged 1-12 years who presented to a Cape Town hospital with abdominal emergencies between 1958-1962, 12.8% of their infections were caused by A lumbricoides, with 68% of those due to intestinal obstruction, usually at the terminal ileum. Peak incidence was at age 2 years in a series from Columbia and age 4.8 years in a series from Turkey. The prevalence of infection in Vietnam is estimated at 44.4%, more commonly in the northern peri-urban and rural areas of the country. In Vietnam, vegetable cultivation using night soil fertilizer makes adult women especially vulnerable. Children with chronic ascariasis may have decreased growth and development due to decreased food intake.
• Adults are more likely to have biliary complications due to migration of adult worms, possibly provoked by other illnesses such as malarial fever. In Damascus, of 300 adults referred for complications of ascariasis between 1988 and 1993, 98% had abdominal pain, 4.3% had acute pancreatitis, 1.3% had obstructive jaundice, and 25% had worm emesis. More than 80% of these patients had a previous cholecystectomy. Another report from India indicated that, of consecutive patients diagnosed with biliary ascariasis, 80% presented with recurrent abdominal pain, 30% with acute cholecystitis, 25% with obstructive jaundice, 25% with cholangitis, and only 5% with pancreatitis, 5% with perforated viscus, and 5% with hepatolithiasis. Only 25% of the Indian patients required surgery. A postcholecystectomy syndrome of pain and jaundice is frequently due to Ascaris in endemic areas, presumably owing to enhanced patency of the biliary system after surgical or endoscopy sphincterotomy.
• Intestinal obstruction, usually of the terminal ileum in children, is the most commonly attributed fatal complication, resulting in 8000-100,000 deaths per year, according to the World Health Organization. Besides direct obstruction of the bowel lumen, toxins released by live or degenerating worms may result in bowel inflammation, ischemia, and fibrosis.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Multimedia
• References

History

• Symptoms include cough, dyspnea, wheezing, and chest pain (during the initial lung migration). This may be seasonal after rains in some countries, such as Saudi Arabia.
• Abdominal pain, distension, colic, nausea, anorexia, and intermittent diarrhea may be manifestations of partial or complete intestinal obstruction by adult worms.
• Jaundice, nausea, vomiting, fever, and severe or radiating abdominal pain may suggest cholangitis, pancreatitis, or appendicitis.

Physical

• Rales, wheezes, and tachypnea may be present during pulmonary migration, particularly if heavily infected. Urticaria and fever may also develop late in the migratory phase.
• Abdominal distension is nonspecific but is often observed in children with worms.
• Abdominal tenderness, especially in the right upper quadrant, hypogastrium, or right lower quadrant, may suggest complications of ascariasis.
• Evidence for nutritional deficiency due to ascariasis is strongest for vitamins A and C, as well as for protein, as manifested by albumin and growth studies in children followed prospectively. Some studies have not confirmed nutritional or developmental delay due to ascariasis.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Multimedia
• References

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Multimedia
• References

Lab Studies

• Stool examination for ova and parasites almost always discloses large, brown 60 X 50 µm trilayered eggs. Fertilized eggs have an uneven mucopolysaccharide coat on their outer surfaces. However, stool examination findings may be negative for up to 40 days after infection because of the time needed for migration and maturation of the worm.
• Larvae may be observed in microscopic wet preparations of sputum during the pulmonary migration phase.
• CBC counts show eosinophilia during the tissue migration phase of the infection.
• Serological tests are not clinically useful.

Imaging Studies

• Chest radiographs may show fleeting opacities during pulmonary migration.
• Abdominal radiographs may show a whirlpool pattern of intraluminal worms. Narrow-based air fluid levels without distended loops of bowel on upright plain films suggest partial obstruction. Wide-based air fluid levels with distended loops suggest complete obstruction. Worms have been increasingly identified in the biliary duct or gallbladder with ultrasonography or CT imaging. Liver granulomata due to A suum have been described as ill-defined, 3- to 35-mm, nodular- or wedge-shaped lesions in the periportal or subcapsular regions.

TREATMENT

Section 6 of 10  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Multimedia
• References

Medical Care

Because of the risk of complications, patients with mixed infections with other worms should always have Ascaris species treated first. Medical therapy is usually not indicated during active pulmonary infection because dying larvae are considered higher risk for significant pneumonitis. Pulmonary symptoms may be ameliorated with inhaled bronchodilator therapy or corticosteroids, if necessary.

• Albendazole 400 mg one dose orally is the drug of choice. Ascaris infection commonly coexists with whipworm infection, which appears to be treated better with albendazole than with mebendazole. Albendazole is not recommended during pregnancy; pyrantel pamoate is the drug of choice in these cases.
• Alternative therapy is mebendazole (100 mg bid for 3 d or 500 mg single dose). Mebendazole is not recommended during pregnancy; pyrantel pamoate is the drug of choice in these cases.
• Paralyzing vermifuges (eg, pyrantel pamoate, piperazine, ivermectin) should be avoided if complete or partial intestinal obstruction is present since the paralyzed worms may necessitate surgery or make surgery more complicated.
• Vitamin A supplementation improved growth development of children in Zaire; deworming did not improve growth development in this study.
• Drug therapy affects only adult worms. If the patient lives in an endemic area or has only recently relocated, he or she may still be carrying larvae that are yet to be susceptible. Such patients should be re-evaluated in 3 months and retreated if stool ova persist. In endemic areas, reinfection may be as high as 80% within 6 months.

Surgical Care

Conservative management of partial intestinal obstruction is usually effective. The patient is kept without oral intake, and the partial obstruction usually spontaneously resolves. Keeping the patient without oral intake lessens the risk of food compounding the obstruction while normal peristalsis redistributes or evacuates the worms. A recent controlled trial from Pakistan indicated that in patients without peritonitis, hypertonic saline enemas were quicker in relieving obstruction (1.6 d vs 3.4 d) and resulted in shorter hospital stays (4 d vs 6 d) than intravenous fluids alone.

• Recommended criteria for surgical exploration
• • Passage of blood per rectum
  • Multiple air fluid levels on abdominal radiographs
  • An ill child with abdominal distension and rebound tenderness
  • Unsatisfactory response to conservative therapy
  • Appendicitis and primary peritonitis
  • Hepatobiliary disease
  • Pancreatic pseudocyst
• Endoscopy has been successfully used to remove obstructing worms from the duodenum and biliary and pancreatic ducts, and now, because of its increased availability, endoscopy probably represents the method of choice for this complication.
• Intestinal or biliary surgery may be necessary for complications of ascariasis.
• • Intestinal gangrene usually occurs at the terminal ileum, more often after use of pyrantel pamoate, which tetanically paralyzes worms and thereby enhances the risk of obstruction. Recently, 2 cases of delayed, distal intestinal disease have been reported, which were thought to be secondary to toxins from the worms. Therefore, patients should probably be monitored for some time after the surgical removal of worms.
  • Milking worms to the large bowel, resection of gangrenous bowel, ileostomy and enterotomy are the most common surgical procedures necessary for bowel obstruction.
  • Invasion of the gall bladder necessitates cholecystectomy, common duct exploration, and T-tube drainage until the patient is stabilized and dewormed.
• Any elective gastrointestinal surgery in patients with ascariasis should be delayed until they have been dewormed and adequately nourished. In particular, patients who live in endemic areas should be dewormed prior to and after elective cholecystectomy.

MEDICATION

Section 7 of 10  

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• Differentials
• Workup
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• Follow-up
• Multimedia
• References

The goals of pharmacotherapy are to eradicate infestation, prevent complications, and reduce morbidity.

Drug Category: Anthelmintic agents

Parasite biochemical pathways are sufficiently different from the human host to allow selective interference by chemotherapeutic agents in relatively small doses.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Multimedia
• References

Transfer

• Patients with partial or complete obstruction should be treated at facilities with surgical support.

Deterrence/Prevention

• Community control has been difficult to achieve. The most successful programs of control, such as those in Japan, have been combined approaches of improved sanitation, night soil disposal, and mass community treatment. Concern has increased for the emergence of drug resistance among heavily retreated populations.
• Japan had a prevalence of 63% in 1949 and essentially eliminated the disease by 1973. Hand washing may be a neglected means of prevention, even in endemic areas, as shown by a recent study from Sri Lanka.
• A program of latrine construction, health education, and twice-annual anthelmintics lowered the prevalence of Ascaris infection in Korea from 80% in 1949 to 55% by 1971. After a 4-year educational campaign and latrine construction in northern Bangladesh, 36% of children aged 5-13 remained infected. Rates of infection were lower among those children who use latrines and have been educated. As rates of infection lessen, specific infected families should be targeted.
• Current treatment strategies recommend repeated mass treatment of communities to reduce intensity of worm burden until socioeconomic progress allows improved sanitation. Although such targeted therapy programs may control the morbidity of infection by decreasing the number of worms per patient, they do not seem to decrease transmission rates. The reinfection rate after a single community campaign in South Africa was 40% at 29 weeks. Children have been targeted in school campaigns, but continued worm burden and shedding by adults have blunted impact. A 6-month educational program directed at behavioral remediation of school children and their parents in Java has shown promise when combined with a deworming campaign.
• Avoiding pigs and pig manure prevents A suum infection in developed countries.
• Work continues on a vaccine. A recombinant, nasally administered 16-kd secretory protein, As16, was shown to result in a 56% decrease in worm burden in mice challenged with A suum larvae.

Prognosis

• Immediate cure rates after single-dose albendazole in South Africa were 95%, with egg reduction rates of more than 99%.
• Most treated patients become reinfected within months unless they are relocated to an area of significantly improved sanitation.

MULTIMEDIA

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Multimedia
• References

Media file 1:  Adult Ascaris lumbricoides.
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Media file 2:  Life cycle of Ascaris lumbricoides.
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Media file 3:  Ascaris lumbricoides egg.
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Media file 4:  Adult Ascaris lumbricoides in biliary system.
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REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Multimedia
• References

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Article Last Updated: Jan 8, 2007