Soil-transmitted Helminths

sOI-uhl trans-mIt-uhd hEl-minth

Collage of whipworm, hookworm and roundworm in petri dishes

Soil-transmitted Helminths (STH) are intestinal worms (“helminth” means parasitic worm) infecting humans that are spread through contaminated soil. STH infection is found mainly in warm and moist climates where sanitation and hygiene are poor. STH are considered neglected tropical diseases (NTDs) because they inflict tremendous disability and suffering yet can be controlled or eliminated.

There are three types of STH that infect a large part of the world’s population: roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura), and hookworm (Ancylostoma duodenale and Necator americanus).


Key Facts

  • Soil-transmitted helminths live in the intestine and their eggs are passed in the stool (poop) of infected people.
  • Hookworm infections often occur in areas where human feces are used as fertilizer or where defecation onto soil happens.
  • Hookworm infection is transmitted primarily by walking barefoot on contaminated soil.
  • Ascariasis is the most common human worm infection, with 800 million to 1.2 billion people affected worldwide.
  • Soil-transmitted helminths are more common in areas where people lack safe access to adequate sanitation.


CDC laboratory technician holds a mass of Ascaris lumbricoides worms
Wormy Situation

A CDC laboratory technician holds a mass of Ascaris lumbricoides worms, which had been passed by a child in Kenya, Africa. Children seem to be infected more often than adults.

Microscopic slide of whipworm
Eggs No One Should Eat

Ingesting whipworm (Trichuris trichiura) eggs leads to a whipworm infestation. These infections are more frequent among children, in areas with tropical weather, and poor sanitation practices.

Photo of six-inch parasite
Pigs Get Sick, Too

Ascaris lumbricoides is the primary parasite that infects humans, while Ascaris suum is the primary parasite that infects pigs. These two parasites are very closely related, and it’s often difficult to tell them apart. Ascaris suum can also make people sick (and pigs can become infected by Ascaris lumbricoides).

Prevention Tips

  • Always wash hands with soap and water after working in the soil and before eating or handling food to help prevent infection from soil-transmitted helminths, especially in areas where sanitation and hygiene may be poor.
  • Avoid ingesting soil that may be contaminated with human feces, including where human fecal matter (“night soil”) or wastewater is used to fertilize crops.
  • Thoroughly wash and peel or cook fruits and vegetables grown in soil that has been fertilized with human fecal matter (“night soil”) or wastewater.
  • The best way to avoid hookworm infection is not to walk barefoot in areas where hookworm is common and where there may be human fecal contamination of the soil. Also, avoid other skin contact with such soil and avoid ingesting it.