There are Some Human Parasites in Soil
Most parasites that infect people don’t pass directly from person to person—though some can spread this way. In general, parasites require time in the environment before they infect another human (the host). A parasite of humans may have another host that it infects between people; for example, the beef tapeworm infects a cow before it infects a human again. Other parasites don’t need an intermediate host, but do need time in the environment—in water, or in soil.
Everyone’s Eating Dirt
Eating dirt doesn’t necessarily mean picking up soil and deliberately putting it in your mouth: we accidentally ingest dirt when we put dirty fingers in our mouths, or eat uncooked vegetables that have not been very thoroughly scrubbed. Soil particles may even be picked up by the wind and inhaled.
How Do Parasites Get Into Dirt?
Put simply, worm eggs and protozoan cysts and oocysts can’t be present in soil unless humans put them there. The commonest ones are passed in the stools of infected people: if they are present in soil, it means that human feces have contaminated the ground. This is an important reason why societies with high standards of sanitation have lower levels of intestinal parasites.
Parasites that can be transmitted by eating dirt can be divided up into helminthes (worms) and protozoa (single celled amoebae and similar organisms).
Worms That You Catch by Eating Dirt
Many people believe that most intestinal worm infections come from eating dirt. Some of the most common do, but only a few species of worms are involved:
- Ascaris lumbricoides: Ascaris is the large intestinal roundworm of humans; it is very common globally, with most infections occurring in tropical regions with warm humid climates. Eggs, passed in stool, are not infective immediately—they need a couple of weeks in soil to mature. If a human swallows a mature egg, the egg will hatch and an intestinal worm results. Ascaris eggs are tough and can survive cold temperatures and exposure to chemicals.
- Trichuris trichiura: Adult trichuris lie threaded into the lining of the large intestine, producing eggs that are passed in stool. Like ascaris eggs, the eggs of this parasite need time in warm moist soil before they are a danger to other humans. They are not as tough as ascaris eggs, so this infection is rarely seen in cooler climates.
- Hookworm, Strongyloides stercoralis and Trichostrongylus spp.: Larvae of these parasites are found in contaminated soil but you don’t need to eat hookworm or strongyloides larvae: they can penetrate bare skin and migrate to the intestine. Larvae of these worms are very sensitive to heat, cold, excess moisture and drying, so they occur only in places where the climate is favorable.
Avoid Parasitic Infections from Dirt
To lower your chances of acquiring parasites from soil:
- wear footwear outside
- do not put soiled fingers or objects in your mouth
- wash fresh fruits and vegetables thoroughly
- do not eat raw fruit and vegetables that you have not washed and peeled yourself in areas where sanitation is poor
- be especially vigilant in places where human feces may contaminate the soil
If you think you may have picked up a parasite, see your doctor for testing and treatment.
Read More About Parasites and Bacteria Found in Soil:
Ascaris lumbricoides—Life Cycle
Toxoplasmosis—Parasitic Disease
Sources:
Diagnostic Medical Parasitology 3rd ed. Garcia, Lynn S. and David A. Bruckner. Washington: ASM Press, 1997.
Foundations of Parasitology 6th Ed. Roberts, Larry S. and John Janovy Jr. Boston: McGraw Hill, 2000.
