Article excerpts about the
causes of Ascariasis:
Almost more than any other parasitic disease, human carelessness causes ascaris. Human feces in streets, fields, and yards are a major source of infective eggs in heavily populated areas. The eggs of ascarids do not infect humans when first excreted by the worm. The eggs are very resistant to extremes of temperature and humidity. They usually are transmitted by hand to mouth, although the use of human feces as fertilizer may also permit transmission of infective eggs by food that is grown in the soil and eaten without being thoroughly washed. The eggs require several weeks to develop and become infective. (Source: excerpt from Parasitic Roundworm Diseases, NIAID Fact Sheet: NIAID)
Other species of ascarids such as Toxocara, which infect dogs and cats, can, under certain circumstances, be picked up by humans. In dogs and cats, these ascarids have a migratory cycle similar to A. lumbricoides. In humans, however, they fail to reach the intestine. Instead they remain active in other body tissue for some time. This state of larval migration is known as visceral larva migrans. (Source: excerpt from Parasitic Roundworm Diseases, NIAID Fact Sheet: NIAID)
As with all medical conditions, there may be many causal factors. Further relevant information on causes of Ascariasis may be found in:
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Both forms of hookworm disease are transmitted to humans through direct skin penetration (usually in the foot) by hookworm larvae in soil contaminated with feces containing hookworm ova. These ova develop into infectious larvae in 1 to 3 days. Larvae travel through the lymphatics to the pulmonary capillaries, where they penetrate alveoli and move up the bronchial tree to the trachea and epiglottis, where they're swallowed and enter the GI tract. When they reach the small intestine, they mature, attach to the jejunal mucosa, and suck blood, oxygen, and glucose from the intestinal wall. These mature worms then deposit ova, which are excreted in the stool, starting the cycle anew. Hookworm larvae mature in approximately 5 to 6 weeks.
Hookworm disease, affecting billions of people worldwide, is most common in moist tropical and subtropical regions. There's little risk of aquiring hookworm disease in the United States because of advances in sanitization and waste control.
Source: Professional Guide to Diseases (Eighth Edition), 2005
A. lumbricoides is a large roundworm resembling an earthworm. It's transmitted to humans by ingestion of soil contaminated with human feces that harbor A. lumbricoides ova. Such ingestion may occur directly (by eating contaminated soil) or indirectly (by eating poorly washed raw vegetables grown in contaminated soil).
Ascariasis never passes directly from person to person. After ingestion, A. lumbricoides ova hatch and release larvae, which penetrate the intestinal wall and reach the lungs through the bloodstream. After about 10 days in pulmonary capillaries and alveoli, the larvae migrate to the bronchioles, bronchi, trachea, and epiglottis. There they are swallowed and return to the intestine to mature into worms.
Ascariasis is most common in tropical areas with poor sanitation and in Asia, where farmers use human feces as fertilizer. In the United States, it's more prevalent in the south, particularly among people ages 4 to 12.
Source: Professional Guide to Diseases (Eighth Edition), 2005
A. lumbricoides is a large roundworm resembling an earthworm. It’s transmitted to humans by ingestion of soil contaminated with human stool that harbors A. lumbricoides ova. Such ingestion may occur directly (by eating contaminated soil) or indirectly (by eating poorly washed raw vegetables grown in contaminated soil).
Ascariasis never passes directly from person to person. After ingestion, A. lumbricoides ova hatch and release larvae, which penetrate the intestinal wall and reach the lungs through the bloodstream. After about 10 days in pulmonary capillaries and alveoli, the larvae migrate to the bronchioles, bronchi, trachea, and epiglottis. There they’re swallowed and return to the intestine to mature into worms.
Source: Handbook of Diseases, 2003
Children commonly get this infection from playing in dirt contaminated with Ascaris eggs.
Source: The 5-Minute Pediatric Consult, 2008
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