Ascaris Lumbricoides (Ascariasis)
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Ascaris lumbricoides is a large parasitic nematode (roundworm), 15 to 40 cm in length, which infects humans via eggs found in soil.
- Geographic distribution: South America, sub-Saharan Africa, China, and East Asia
- All ages may be affected; however, children are more frequent hosts owing to oral behavior and tend to have a higher worm burden.
- Ascariasis is more common where sanitation is poor and population is dense.
- Eggs are viable in the soil for >6 years in temperate climates.
- It is the most prevalent helminth infection in the world.
- 800 million cases worldwide and estimated 400 million children infected
- Around 51 million children suffer severe morbidity, mostly from moderate and heavy worm loads.
- Sanitary disposal of human excrement, not using human feces as fertilizer, and hand washing has the potential to eliminate this infection.
- In communities with high transmission of Ascaris, community-wide mass drug delivery of anthelmintics is effective in controlling morbidity.
- Fertilized eggs are ingested from soil contaminated with human feces.
- Larvae hatch in the small intestine and migrate to cecum and colon.
- Larvae invade the mucosa into the venous system and travel to the portal circulation, inferior vena cava, and finally, pulmonary capillaries.
- During migration through the pulmonary vessels, an eosinophilic response is evoked.
- Larvae penetrate the alveoli, are expelled by coughing, and swallowed back (days 10 to 14).
- Larvae become adult worms in the small intestine (day 24).
- Female worms excrete up to 200,000 eggs per day.
- Ingestion to excretion takes 2 to 3 months.
- Once in soil, fertilized eggs require 2 to 3 weeks of incubation in soil to become infectious and restart cycle.
Children commonly acquire this infection from playing in dirt contaminated with Ascaris eggs.
Commonly Associated Conditions
This infection may be associated with other soil-transmitted helminths:
- Hookworm (Necator americanus, Ancylostoma duodenale)
- Trichuris trichiura
- Strongyloides stercoralis
- Toxocara canis