How Are Round Worms Spread to Humans?
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What are Round Worms?
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"Round worm" is actually an umbrella term for about 15,000 species of disease-causing parasitic worms known as "nematodes." The symptoms for round worm infections are grouped into one of six disease categories: ascariasis, hookworm, pinworm, strongyloidiasis, trichinosis and whipworm. These disease categories follow one of four different modes of transmission: through the skin of the feet, eating soil-tainted food, eating infected meat and from hand to mouth.
Walking Barefoot on Feces-Contaminated Ground
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The leading cause of ascariasis, stronglyoidiasis and hookworm, nematode larva hatched in human/animal feces attach to the skin on the sole of the foot and burrow up into the bloodstream. Once in the circulatory system, they are carried into the heart by the venae cavae and then move into the lungs. This causes coughing that expels the larva into the mouth/throat. When the victim swallows, the larva are taken down into the intestines where they enter the next stage of their life cycle: reproduction.
This mode of transmission is common in areas where poor or non-existent sanitation systems allow raw sewage to flow in the street. Also, using untreated feces as fertilizer contaminates the soil. In this way, barefooted farmers can contract round worms while working in the field.
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Eating Food Tainted by Feces-Contaminated Soil
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As mentioned above, farmland fertilized with untreated feces can easily become contaminated with round worm larva. Whipworm eggs do not hatch in the soil; rather, these microscopic particles rub off on beans, rice and other grains. Able to survive for weeks, even in extreme conditions, the eggs enter the small intestine when the victim eats the contaminated food without first washing it thoroughly.
Eating the Meat of an Infected Animal
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Trichinosis has the ignoble distinction of being able to survive in the intestines and muscle tissue of virtually any meat-eating animal. Scavengers (rats, raccoons, wolverines) and swine who are fed garbage are the most likely to consume the carcass/cooked meat of an animal infected with Trichinella spiralis nematode larva. Once in the stomach, larva mature and mate. The female then enters the blood stream and lodges in a narrow muscle capillary where she lays eggs in the muscle tissue. As part of the host's immune response, a cyst forms around the foreign object (the egg). Inside the cyst, the eggs safely hatch into larva, waiting for the host to be consumed by a predator.
Accidentally Ingesting Eggs Trapped on Fingertips
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Pinworm and whipworm can be contracted when their invisible eggs are transferred from the host's fingertips to his food right before he eats it. In the case of the whipworm, the eggs originate from feces-contaminated soil used for farming. Farmers whose hands touch either the soil or the produce grown in the soil run the risk of picking up whipworm eggs on their fingers. Unless they thoroughly wash with soap and water, the eggs will remain.
Pinworm transmission is a bit more insidious. Once impregnated, the female travels to the anus and lays thousands of eggs on the anal sphincter. She then releases a special toxin designed to create an intense itching sensation in and around the anus. When the host scratches his peri-anal area to calm the itch, hundreds of eggs attach to his finger. Meanwhile, hundred more could spill out onto bedsheets, clothes and (in rare cases) furniture upholstery. If the host or anyone whose hands come in contact with the contaminated fabrics handles their food without washing their hands, the eggs could easily be picked up by the food and swallowed.
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