Ascaris lumbricoides - MegaMicro

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Ascaris lumbricoides

Micro > Parasitology > Nematodes
1. Structure
a. Round worm
b. Largest nematode parasitizing the human intestine
c. Adult females: 20-35 cm; adult male: 15-30 cm

2. Pathobiology:
a. Fecal-oral transmission
b. Ingest eggs, and larvae hatch in the intestine. Larvae can then travel through the blood to the lung. Larvae will mature in the lung where they are coughed up and then swallowed. Mature worms will then establish infection in the gut where they can produce eggs that will be passed via stool.

3. Epidemiology
a. Most common helminthic infection
b. Worldwide distribution
c. Highest prevalence in tropical/subtropical regions and areas with inadequate sanitation
d. Seen in rural areas of the southeastern US

4. Laboratory diagnosis
a. Microscopic ID of eggs via stool sample: direct wet mount examination of the specimen is adequate for detecting moderate to heavy infections.  For quantitative assessments of infection, various methods such as the Kato-Katz can be used.
b. Larvae can be identified in sputum/gastric aspirate during pulmonary migration phase (examine formalin-fixed organisms for morphology)
c. Adult worms usually passed in stool or through mouth or nose

5. Disease manifestations
a. Infection may cause stunted growth
b. Adult worms will often cause no acute symptoms
c. High worm burdens may cause ascariasis
i. Most common cause of Loeffler’s syndrome – symptoms include: cough, dyspnea, hemoptysis, eosinophilic pneumonitis
1. Results from migration of worms to the lungs causing Type 1 hypersensitivity
ii. Intestinal obstruction or occlusion of the appendix
iii. Bowel perforation
iv. Peritonitis from worm burrowing
v. Cholecystitis from migration into bile duct

6. Therapy
a. Albendezole, mebendezole
b. Treatment lasts for 1-3 days
i. Few side effects, drugs appear to be effective

Related concepts
1. Ascaris lumbricoides
2. Nematode
3. Loeffler’s syndrome

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