Ascaris lumbricoides

Introduction

The largest nematode that infects the intestinal tract of humans. May grow as long as 35 cm.

Epidemiology

• most common nematode infection
• world-wide distribution
• occurs primarily in areas with poor sanitation
• occurs most frequently in children
• unembryonated eggs are passed in the feces of the host
• eggs require 4-6 weeks in an appropriate environment to become infectious (embryonated)
• worms do not multiply in host but may live 2 years in the small intestine
  • re-eoxposure required for re-infection

Pathology

• ingested eggs hatch in the intestine & larvae penetrate the intestinal mucosa to gain access to the bloodstream
• larvae are carried to the lungs where they mature rapidly in the alveolar capillary bed before entering the alveoli
• respiratory clearance mechanisms move the larvae to the epiglottis where they are swallowed
• larvae attach to the mucosa of the small intestine where they develop into adult worms
• development from an embryonated egg to an adult takes about 2 months
• adult worms live primarily in the duodenum & proximal jejunum
• females measure up to 35 cm in length by 6 mm in diameter
• the male is somewhat smaller & unlike the female has a ventrally curved tail
• A. lumbrocoides may be identified by the presence of 3 prominent lips at the anterior end
• female produce 200,000 eggs/day which pass unembryonated in the feces
• Ascaris may invade ectopic sites including the common bile duct, liver, appendix & stomach
• fever or drug therapy may stimulate migration

Clinical manifestations

• vary from asymptomatic to severe disease
• migration of large numbers of larvae through the lungs may cause pneumonitis (Loffler's syndrome)
• abdominal pain & diarrhea may accompany heavy infestations

Laboratory

• diagnosis is made by recovery of eggs or an adult in the feces
  • Kato-Katz thick smear to identify eggs in endemic areas
• eggs*
  • round to slightly oval with a yellow-brown, irregular external mamillated layer & a thick shell
  • 55-75 by 35 to 50 um
  • unfertilized eggs are larger, up to 90 um in length & with a thinner shell & irregular mammillations
  • unfertilized eggs are filled with fat globules
  • egg counts of < 10 eggs/ mg feces (1/2 slide) indicate a light infection, > 100 eggs/ mg feces indicates a heavy infection
• 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

Radiology

• abdominal radiography
  • nonobstructive bowel gas pattern with thickened colonic haustra
• abdominal CT (images)
  • tubular structures filling the small bowel

Complications

• coinfection with Trichuris trichiura
• intestinal obstruction &/or pancreatic obstruction may occur with a mass of worms especially in children
• hepatobiliary injury
• mortality is increased with a superimposed bacterial infection

Management

• in endemic areas, antihelmintics are prescribed prior to use of anesthetic in elective surgery
• antihelmintics should be given to prevent complications
  • when cholangitis is present, antibiotics should be administered first
  • antihelmintics
    • mebendazole
    • albendazole
    • pyrantel pamoate or piperazine citrate during pregnancy
• partial obstruction
  • nasogastric suction
  • intravenous fluids
  • piperazine administration through the NG tube
• immediate surgical intervention for complete bowel obstruction

Notes

* surgical image

More general terms

• Ascaris

Additional terms

• Loffler's syndrome (simple pulmonary eosinophilia)