Intestinal worms

Epidemiology

Geographical distribution


Soil-transmitted helminth infections are widely distributed in tropical and subtropical areas and, since they are linked to a lack of sanitation, occur wherever there is poverty.

Transmission cycle

People infected with soil-transmitted helminths have parasite eggs in their faeces. In areas where there are no latrine systems, the soil (and water) around the village or community becomes contaminated with faeces containing worm eggs.

In the soil, the eggs mature – a process that takes between 2 and 4 weeks, depending on the type of worm:

  • about 2 weeks for roundworms and hookworms;
  • about 3 weeks for whipworms.

The worms can then infect humans in the following ways:

  • The eggs stick to vegetables grown in the area. If the vegetables are not carefully cooked, washed or peeled, the eggs are ingested and infect the person.
  • The eggs are ingested from water sources which have become contaminated.
  • Young children who play on the ground and often put their hands in their mouths without washing them, ingest the eggs and become infected.

The larvae penetrate the skin:

  • For hookworms, the eggs also hatch into larvae which rest in the soil. If a person walks on the contaminated soil, the larvae can penetrate the skin, usually between the toes.

There is no direct person-to-person transmission or infection from fresh faeces because eggs passed in faeces need about 3 weeks in the soil before they become infective.

Global Health Observatory (GHO)

Neglected tropical diseases (NTDs) blight the lives of a billion people worldwide and threaten the health of millions more.

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