Nematode - Ascaris lumbricoides
Ascaris lumbricoides
- Largest roundworm of human intestine parasites (15-30 cm long).
- Most common helminthic infection.
- Found worldwide, but especially in tropical and subtropical areas; rural southeastern US.
- Esp. places with poor sanitation, use of human feces as fertilizer. This leads to food contamination.
- Can be asymptomatic or mild.
- Serious infections occur when adults invade bile ducts, gallbladder, liver, appendix.
- Can cause malabsorption and stunted growth in children (competes for nutrients, and can block intestines).
- Because the larvae migrate to the lungs, and eosinophil counts increase, infected people can have cough and pulmonary infiltrates (Loffler’s syndrome); outside the GI, the immune system responds by increasing eosinophils.
- Diagnosis = eggs in feces; larvae may be present in sputum.
Life cycle:
- Human host infests infective eggs (contaminated food).
- Eggs reach small intestine, larvae hatch.
- Larvae move through wall of small intestine, travel in blood to the lungs.
- In the alveoli of the lungs, larvae grow.
- Host coughs larvae, swallows them.
- In the small intestine, the larvae mature into adults.
- Adults produce 1000s of eggs each day.
- Fertilized and unfertilized eggs are passed in stool
- Fertilized eggs develop (differentiate into embryo) in environment and can infect new host.