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Ascaris lumbricoides

The largest nematode that infects the intestinal tract of humans. May grow as long as 35 cm. [4] Epidemiology: 1) most common nematode infection 2) world-wide distribution 3) occurs primarily in areas with poor sanitation 4) occurs most frequently in children 5) unembryonated eggs are passed in the feces of the host 6) eggs require 4-6 weeks in an appropriate environment to become infectious (embryonated) 7) worms do not multiply in host but may live 2 years in the small intestine [4] - re-eoxposure required for re-infection [4] Pathology: 1) ingested eggs hatch in the intestine & larvae penetrate the intestinal mucosa to gain access to the bloodstream 2) larvae are carried to the lungs where they mature rapidly in the alveolar capillary bed before entering the alveoli 3) respiratory clearance mechanisms move the larvae to the epiglottis where they are swallowed 4) larvae attach to the mucosa of the small intestine where they develop into adult worms 5) development from an embryonated egg to an adult takes about 2 months 6) adult worms live primarily in the duodenum & proximal jejunum 7) females measure up to 35 cm in length by 6 mm in diameter 8) the male is somewhat smaller & unlike the female has a ventrally curved tail 9) A. lumbrocoides may be identified by the presence of 3 prominent lips at the anterior end 10) female produce 200,000 eggs/day which pass unembryonated in the feces 11) Ascaris may invade ectopic sites including the common bile duct, liver, appendix & stomach 12) fever or drug therapy may stimulate migration Clinical manifestations: 1) vary from asymptomatic to severe disease 2) migration of large numbers of larvae through the lungs may cause pneumonitis (Loffler's syndrome) 3) abdominal pain & diarrhea may accompany heavy infestations Laboratory: 1) diagnosis is made by recovery of eggs or an adult in the feces - Kato-Katz thick smear to identify eggs in endemic areas [4] 2) eggs* a) round to slightly oval with a yellow-brown, irregular external mamillated layer & a thick shell b) 55-75 by 35 to 50 um c) unfertilized eggs are larger, up to 90 um in length & with a thinner shell & irregular mammillations d) unfertilized eggs are filled with fat globules e) egg counts of < 10 eggs/ mg feces (1/2 slide) indicate a light infection, > 100 eggs/ mg feces indicates a heavy infection 3) Ascaris lumbricoides serology - Ascaris lumbricoides IgE in serum - Ascaris lumbricoides IgG in serum - Ascaris lumbricoides IgG adult in serum - Ascaris lumbricoides IgG larva in serum - Ascaris lumbricoides IgM in serum * image [6] Radiology: - abdominal radiography - nonobstructive bowel gas pattern with thickened colonic haustra - abdominal CT (images [3]) - tubular structures filling the small bowel Complications: - coinfection with Trichuris trichiura [3] - intestinal obstruction &/or pancreatic obstruction may occur with a mass of worms especially in children [4] - hepatobiliary injury [4] - mortality is increased with a superimposed bacterial infection [5] Management: 1) in endemic areas, antihelmintics are prescribed prior to use of anesthetic in elective surgery 2) antihelmintics should be given to prevent complications a) when cholangitis is present, antibiotics should be administered first [5] b) antihelmintics - mebendazole - albendazole - pyrantel pamoate or piperazine citrate during pregnancy 3) partial obstruction a) nasogastric suction b) intravenous fluids c) piperazine administration through the NG tube 4) immediate surgical intervention for complete bowel obstruction Notes: * surgical image [4,6]

Related

ascariasis Loffler's syndrome (simple pulmonary eosinophilia)

General

Ascaris

Properties

KINGDOM: animal PHYLUM: helminth

References

  1. Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 1284-85
  2. Harrison's Principles of Internal Medicine, 13th ed. Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 916-17
  3. Blount T, Hartsell A. Tubular Opacities in the Gastrointestinal Tract. N Engl J Med 2017; 377:2375. December 14, 2017 PMID: 29236643 Free full text http://www.nejm.org/doi/full/10.1056/NEJMicm1703094
  4. Grimm L What's Eating You: 12 Common Intestinal Parasites. Medscape. November 25, 2019 https://reference.medscape.com/slideshow/intestinal-parasites-6010996
  5. Zhang A, Chung H, Gong T Fever, Abdominal Pain, and Jaundice in a Pacific Islander Woman. JAMA. 2020;323(3):272-273 PMID: 31841586 https://jamanetwork.com/journals/jama/fullarticle/2757849
  6. Grim L You've Got Worms! Common Intestinal Parasites Medscape. Jan 23, 2023 https://reference.medscape.com/slideshow/intestinal-parasites-6014593