The problem

Shading represents the numbers of children requiring preventative treament for soil-transmitted helminths in 2015. © WHO

The World Health Organization estimates one in five people are infected with soil-transmitted helminths (STHs) worldwide.

This includes 845 million - 44 percent - of the world's children.

What are soil-transmitted helminth infections?

Soil-transmitted helminths (STHs) are a group of intestinal parasites that thrive in areas with warm, humid soil and poor sanitation.

STHs are common in tropical and subtropical areas, especially in sub-Saharan Africa, the Americas and East Asia, where some communities do not have access to adequate water and sanitation.

The most common STH parasites are

  • roundworm (Ascaris lumbricoides)
  • hookworm (Necator americanus, Ancylostoma duodenale)
  • whipworm (Trichuris trichiura).

How are STHs transmitted ?

Adult STHs maturing in the intestine produce thousands of eggs a day.

STHs are transmitted when infected people shed eggs in faeces that then contaminate soil or water and are ingested by others or actively penetrate their skin as larval worms.

Additionally, hookworm eggs can hatch in the soil and release larvae that mature and are capable of actively penetrating the skin of bare feet.

Ascaris lumbricoides worms

Ascaris lumbricoides worms from a child in Kenya © CDC/ James Gathany


Adult worms and eggs infect a person's gut reducing the uptake of nutrients and vitamins leading to 

  • malnutrition 
  • anaemia
  • stunted growth
  • impaired cognitive development
  • an increased susceptibility to other infectious diseases