Ascaris lumbricoides evolved with humans, and it lives in the intestines of millions of people. Large and active, it has inspired many tales and considerable folklore.
Ascaris lumbricoides is otherwise known as the large intestinal roundworm of humans. It looks a lot like a large earthworm, but the two are not even related. The earthworm is an annelid; it lives in the soil, feeding on organic debris. A. lumbricoides is a parasitic nematode, or roundworm; adults are found only in the intestines of humans, feeding on intestinal contents as they flow past. If you were to compare the two very carefully, you would note that the earthworm has little tufts of bristles and its body is marked with many rings, as though it was built a slender ring at a time. The body of ascaris is smooth and hairless, and the worm has three lips at the mouth end, arranged like the leaves of a three leaf clover.
Ascaris lumbricoides worms have a reputation for wandering, and often do so if the body they are in—the host—is ill or taking certain medications. Adult roundworms sometimes spontaneously exit the host through the anus, mouth, or nose. They are found in the bathtub, toilet bowl, in diapers, or even on the pillow upon waking. Females can be well over a foot long; males are smaller. For many people, the appearance of a large worm is a traumatic experience, and no doubt the source of many tales about worms.
Misconceptions and myths about Ascaris lumbricoides
Because of it's frequent appearances, A. lumbricoides has been familar to people for thousands of years. Here are some commonly held, but incorrect, beliefs about ascaris:
- You can catch Ascaris lumbricoides from your dog or cat. False: the intestinal roundworms of dogs and cats are different species that are never found as worms in the human intestine. The large intestinal roundworm of pigs may be able to live in humans but this has not been proven. Ascaris infection is acquired when the host swallows worm eggs that have matured in warm moist soil after an infected person defecated on the ground.
- Putting a piece of bread or raw steak by a person’s mouth will lure the worms out. False: ascaris worms do sometimes exit the mouth but they do not eat bread and steak. These animals are adapted to get nutrients by taking in liquid intestinal contents.
- Having ascaris worms will make you lose weight. False: a few worms in the intestine generally cause no obvious symptoms at all. Many worms may lead to nutritional deficiency, particularly in children, or bowel blockage due to worms forming balls and knots of many individuals.
Ascaris lumbricoides in history
People have known about A. lumbricoides for a long time. Since antiquity we have been trying to understand them, prevent them, and cure them. Here are some interesting facts from the history of ascaris:
- Prior to about 1600, many people believed that ascaris was spontaneously generated in the intestine; in other words, people actually produced the worms themselves.
- In both Europe and the Far East it was long believed that an ascaris worm entering the heart would cause sleep walking on moonlit nights and sometimes sudden death.
- Ascaris worms—ground, juiced, burned to ash, dried, or even partially decomposed—were used in ancient Chinese medicine to treat eye problems. They were used in many countries to treat worm infections, and in some cultures as an aphrodisiac.
- Ascaris lumbricoides eggs have been found in fossilized human feces all over the world. The oldest are thought to be nearly 30,000 years old.
Because of ascaris’ potential to wander and do damage to internal organs, and because it is associated with malnutrition and learning problems in children, an ascaris infection should always be treated. If you suspect you have intestinal worms, see your doctor.
Related content:
Ascaris lumbricoides - Life Cycle
Read about other nematodes that infect humans:
Other interesting articles about human infections are available in Microbiology
Sources:
Parasites and Parasitic Infections in Early Medicine and Science. Hoeppli, R. Singapore: University of Malaya Press, 1959.
Foundations of Parasitology 6th Ed. Roberts, Larry S. and John Janovy Jr. Boston: McGraw Hill, 2000.
