Ascaris are one of the larger worms that infect humans. (My personal favorite, Guinea Worm, are much longer, but I'll get to those later.) The females can reach lengths of 40 cm inside the intestine. They are typically found in younger children, as those are the most likely to be ingesting dirt. (Accidentally or purposefully.)
Ascaris have to live in the soil for a few weeks before they can reach their infective stage. They have very thick eggs, with distinctive "mammilations" on the outside (this means the outer surface is very bumpy). This allows them to survive for a longer time, and in worse conditions than an egg with a thin shell, like hookworm eggs. The eggs are passed out with feces, and mature in the soil. They can then be eaten by their preferred host, us! The eggs then travel to the upper small intestine, where they hatch. These small larva then penetrate the gut wall, and move through the blood and lymph systems to the lungs. Here they enter the alveoli and continue to grow. Once they have reached the final larva form, the begin to irritate the lungs, causing coughing. This allows them to travel up the windpipe, where they can then be swallowed, so they eventually end up where they wanted to be - the small intestine. Here they mate and start producing lots of little baby Ascaris eggs.
The irritation of the lungs can cause a symptom known as Loefflers. It closely resembles asthma, and can easily be mis-diagnosed. It is caused by an allergic reaction to the worms.
Most cases of Ascaris lumbricoides infection go unnoticed. There is little chance for re-infection, so once the adult worms have all died (sometimes this can take as long as 2 years), the original infection will go away. Since they are only eating the fecal stream (yum), they rarely take away noticeable amounts of nutrients from the body. However, problems can occur when there are massive infections, as the worms may cause blockages in the intestine. This is also why it is important to know which worms you have, as some anti-helminthic medicines work by causing the worms to clump together, which you would not want to do if you had a mega infection. Moderate infections can cause upset stomachs, some stomach pain, and some nausea. More problems can occur when the worms migrate out of the intestine, something which does not normally happen. However, Ascaris REALLY don't like anesthesia. In the case of the host being anesthetized, the worms will suddenly start to flee the body via any opening they can find. Unfortunately, this can include the nose, mouth, tear ducts, and anus. They can also try to flee into other organs, such as the appendix, which can cause appendicitis.
Diagnosis involves searching for the eggs in feces, or by seeing the adult worms coming out of the body. If a lung infestation is suspected, a biopsy can be taken of lung tissue and examined for worms.
Drugs that paralyze the worm and allow them to pass out of the body, such as piperazine, are the best. Surgery may be required in cases of obstruction, or if the worm has migrated to an unusual spot.
The easiest way to prevent Ascaris infection is flush toilets. If human feces are not allowed to sit around long enough for the eggs to develop, and then for people to ingest them again, then the worm cannot spread.
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