Intestinal worms


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

Figure schematic life-cycle (source: helminth control in school age children)

Soil-transmitted helminths live in the intestine of infected individuals where they produce thousands of eggs each day that are passed in the faeces. Where the environmental conditions are favourable, the eggs develop into infective stages.

Humans become infected when ingesting infected eggs (Ascaris lumbricoides and Trichuris trichiura) or larvae (Ancylostoma duodenale) in contaminated food (e.g. vegetables that are not carefully cooked, washed or peeled), hands or utensils or through penetration of the skin by infective hookworm larvae in contaminated soil (Necator americanus and Ancylostoma duodenale).

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.

Although strongyloidiasis has a similar route of infection as the other soil-transmitted helminthiases, it needs different diagnostic tools and different treatment.

In areas where mass treatment with ivermectin has been used to control onchocerciasis or lymphatic filariasis, there has been a noticeable reduction in the prevalence of strongyloidiasis.

The possibility of use this approach for the control of infection is presently under evaluation.

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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