Ascariasis is the most common helminthic infection, with an estimated worldwide prevalence of 25% (0.8-1.22 billion people).[1] Usually asymptomatic, ascariasis is 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.[2] For more information on ascariasis in children, see the Medscape article Pediatric Ascariasis. Symptomatic ascariasis may manifest as growth retardation, pneumonitis, intestinal obstruction, or hepatobiliary and pancreatic injury. In developing countries, ascariasis may exist as a zoonotic infection in pigs, but little evidence has shown transmission of porcine ascariasis to humans.[3]
The image below depicts a roundworm that infects humans through soil contaminated by human feces.
Ascaris lumbricoides is the largest of the common nematodes (roundworms) that infect humans. Adult A lumbricoides are white or yellow and 15-35 cm long (see first image below). They live 10-24 months in the jejunum and middle ileum of the intestine. Each day, female A lumbricoides produce 240,000 eggs (see second image below), which are fertilized by nearby male worms. A Chinese study 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.[4] 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 (see third image below).
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Adult Ascaris lumbricoides.
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Ascaris lumbricoides egg.
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Life cycle of Ascaris lumbricoides.
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 significant 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 they mature into adults in approximately 65 days.
Adult worms feed on digestion products of the host. Children with a 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.[5] Large and tangled worms may cause intestinal (usually ileal), common duct, pancreatic, or appendiceal obstruction. Mean worm burden varies from more than 16 to 4 and appears related to host factors, particularly age, geophagy,[6] and immunity. Worms do not multiply in the host. For infection to persist beyond the 2-year maximum lifespan of the worms, re-exposure must occur.
Ascaris lumbricoides suum, a swine nematode, has been thought responsible for zoonotic infection. Distinguishing this worm from A lumbricoides is difficult. A suum appears to responsible for most ascariasis cases in well-developed countries with excellent sanitation (eg, Denmark,[7] United States, UK[8] ). In this setting, infected children have a low worm burden and may present with only acute eosinophilia or eosinophilic liver lesions visible on CT scans. However, a molecular genetic study from China casts doubt that infections in pigs are a significant reservoir for human infection.[3]
In 1974, an estimated 4 million people, mainly in the southeast United States, had ascariasis. Recent estimates of ascariasis prevalence are unknown, but probably much lower. Immigrants from countries with a high prevalence of ascariasis comprise most recent cases.
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. A recent Vietnamese study found that adult women living in rural areas, especially those exposed to human night soil and living in households without a latrine, were at surprisingly high risk for ascariasis.[9] The Centers for Disease Control and Prevention (CDC) estimated that worldwide ascariasis rates in 2005 were as follows: 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 adult worms in the intestine is only one year, persistent infection requires frequent re-exposure and reinfection. The frequency and intensity of infection remain high throughout life in endemic areas and pose a risk to both elderly and young persons. In a recent study in rural southwest Nigeria, the intensity of excreted eggs per gram of feces among infected persons was 2,371 for Ascaris species, 1070 for hookworm, and 500 for Trichuris species, with only slightly lower rates among persons in urban areas.[10] Estimates of disability-adjusted years of life due to ascariasis have fallen because of development and management programs during the 1990s, especially in Asia, but still constitute a significant burden in some countries.
Mortality/Morbidity
Ascariasis is most common and intensive in children, who are more likely than adults to be symptomatic. In children, intestinal obstruction caused by heavy worm burden (≥60) is the most common manifestation of disease. An estimated 2 per 1000 infected children develop intestinal obstruction per year.[11] Among children aged 1-12 years who presented to a Cape Town hospital with abdominal emergencies between 1958-1962, symptomatic A lumbricoides infection was responsible for 12.8% of cases , with 68% of those due to intestinal obstruction, usually at the terminal ileum. The peak incidence was at age 2 years in a series from Colombia 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.[12] In Vietnam, vegetable cultivation using night soil fertilizer places adult women at especially high risk. Children with chronic ascariasis may experiencedecreasedgrowthanddevelopment due to decreased food intake.
Adults with ascariasis are more likely to develop biliary complications due to migration of adult worms (see image below), 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. Twenty-one to 80% of patients had undergone previous cholecystectomy or endoscopic sphincterotomy.
A recent review of biliary ascariasis suggests that this association may be causative as a result of dilatation of the common bile duct and elevation of cholecystokinin levels with resultant relaxation of the sphincter of Oddi.[13] A 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 ascariasis in endemic areas, presumably owing to enhanced patency of the biliary system after surgical or endoscopic sphincterotomy.[14]
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Adult Ascaris lumbricoides in biliary system.
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.
Early symptoms of ascariasis, during the initial lung migration, include cough, dyspnea, wheezing, and chest pain. 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.
Rales, wheezes, and tachypnea may develop during pulmonary migration, particularly in persons with a high worm burden. Urticaria and fever may also develop late in the migratory phase.
Abdominal distension is nonspecific but is common in children with ascariasis.
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 indicated by albumin and growth studies in children observed prospectively. Some studies have not confirmed nutritional or developmental delay due to ascariasis.
Stool examination for ova and parasites almost always discloses large, brown 60 µm X 50 µm trilayered eggs in persons with ascariasis. However, stool examination may be negative for ova for up to 40 days after infection because of the time needed for migration and maturation of the worm. The outer surfaces of fertilized eggs have an uneven mucopolysaccharide coat.
Ascaris 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 for ascariasis.
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 and CT scanning.[15] Liver granulomata due to A suum infection have been described as ill-defined, 3- to 35-mm, nodular- or wedge-shaped lesions in the periportal or subcapsular regions.
Endoscopic retrograde cholangiopancreatography (ERCP) has become a commonly used procedure for both diagnosis of ascariasis and removal of worms from the biliary tract. The ease of diagnosis and therapy in the same setting makes ERCP particularly valuable when used with real-time ultrasonography. The combined procedures yield a sensitivity of nearly 100%.[13]
Because of the risk of complications, patients with ascariasis who have other concomitant helminthic infections should always undergo treatment for ascariasis first. Medical therapy is usually not indicated during active pulmonary infection because dying larvae are considered a 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. Ascariasis commonly coexists with whipworm infection, which appears to be more susceptible to albendazole than to 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 as a 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 in patients with complete or partial intestinal obstruction since the paralyzed worms may necessitate or further complicate surgery.
Vitamin A supplementation improved growth development of children in Zaire; deworming did not improve growth development in this study.[16]
Drug therapy affects only adult worms. If the patient lives in an endemic area or has recently relocated, he or she may still be carrying larvae that are not yet susceptible. Such patients should be re-evaluated in 3 months and retreated if stool ova persist. In endemic areas, reinfection rates approach 80% within 6 months.
Nitazoxanide, a drug used primarily for protozoal infection, was shown to have 89% clinical efficacy for the treatment of ascariasis in rural Mexico and may offer a future alternative to other medications.[17]
Conservative management of partial intestinal obstruction and biliary ascariasis is usually effective. The patient is maintained on nothing-by-mouth status, and the partial obstruction usually spontaneously resolves. Preventing oral intake decreases the risk of food compounding the obstruction while normal peristalsis redistributes or evacuates the worms. A controlled trial from Pakistan found that, in patients without peritonitis, hypertonic saline enemas relieved obstruction more quickly (1.6 d vs 3.4 d) and resulted in shorter hospital stays (4 d vs 6 d) than intravenous fluids alone. A recent study from India demonstrated that conservative therapy was successful in 19 of 22 (89%) children with intestinal obstruction. The regimen used consisted of no oral intake, intravenous fluids, antibiotics, piperazine salt per nasogastric tube, and glycerine plus liquid paraffin emulsion enemas.[11]
Recommended criteria for surgical exploration include the following:
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
Most (49-90%) worms eventually migrate from the biliary system spontaneously. Drug therapy should be delayed in patients with right upper quadrant or pancreatic pain, as no evidence has shown that drugs are active against worms located in the biliary tree. Regardless, death of the worm in the duct may provoke both inflammation and obstruction. Patients with ascariasis who have only minor symptoms can undergo observation for 3 days. If the minor symptoms persist after 3 days or the patient develops frank cholangitis or pancreatitis, removal of the worms with ERCP should be attempted, if available. Although technically challenging at times, ERCP extraction rates have exceeded 90%.[13]
Intestinal or biliary surgery may be necessary for complications of ascariasis.
Intestinal gangrene usually occurs at the terminal ileum, more often after the 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 of worms to the large bowel, resection of gangrenous bowel, ileostomy, and enterotomy are the most common surgical procedures used to manage 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 before and after elective cholecystectomy.
Clinical Context:
First DOC. A benzimidazole carbamate drug that inhibits tubulin polymerization, resulting in degeneration of cytoplasmic microtubules. Decreases ATP production in worms, causing energy depletion, immobilization, and, finally, death. Converted in the liver to its primary metabolite, albendazole sulfoxide. Less than 1% of the primary metabolite is excreted in the urine. Plasma level is noted to rise significantly (as much as 5-fold) when ingested after high-fat meal. Experience with patients < 6 y is limited.
To avoid inflammatory response in CNS, patient must also be started on anticonvulsants and high-dose glucocorticoids.
Well tolerated and does not appear to increase risk of worm obstruction.
Clinical Context:
Well tolerated and does not appear to increase risk of worm obstruction. Causes worm death by selectively and irreversibly blocking uptake of glucose and other nutrients in susceptible adult intestine where helminths dwell.
Parasite biochemical pathways are sufficiently different from the human host to allow selective interference by chemotherapeutic agents in relatively small doses.
Community control of ascariasis has been difficult to achieve. The most successful control programs, such as those in Japan, have consisted of combined approaches, including improved sanitation, night soil disposal, and mass community treatment. Concern has increased for the emergence of drug resistance among heavily retreated populations.
The prevalence of ascariasis in Japan in 1949 was 63%; the disease was essentially eliminated 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 decreased the prevalence of ascariasis in Korea from 80% in 1949 to 55% by 1971. After a 4-year educational campaign and latrine construction program in northern Bangladesh, 36% of children aged 5-13 remained infected. Rates of infection were lower among children who used latrines and who had been educated concerning the risks of ascariasis.[18] As rates of ascariasis lessen, specific infected families should be targeted.
Current ascariasis 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 ascariasis by decreasing the number of worms per patient, they do not seem to decrease transmission rates. The ascariasis 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.[19]
David R Haburchak, MD, Program Director, Professor, Department of Internal Medicine, Division of Infectious Disease, Medical College of Georgia
Disclosure: Nothing to disclose.
Specialty Editors
Jeffrey D Band, MD, Professor of Medicine, Oakland University William Beaumont School of Medicine; Director, Division of Infectious Diseases and International Medicine, Corporate Epidemiologist, William Beaumont Hospital; Clinical Professor of Medicine, Wayne State University School of Medicine
Disclosure: Nothing to disclose.
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Medscape Salary Employment
Richard B Brown, MD, FACP, Chief, Division of Infectious Diseases, Baystate Medical Center; Professor, Department of Internal Medicine, Tufts University School of Medicine
Disclosure: Nothing to disclose.
Chief Editor
Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
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