Soil-transmitted helminthiases are caused by infection with the nematodes Ascaris lumbricoides (roundworm), Trichuris trichiura (whipworm) and Ancylostoma duodenale or Necator americanus (hookworms) and are among the commonest infections in humans. Those living in poverty are most vulnerable to infection.
In warm, tropical environments, where soil-transmitted helminthiases are endemic and where sanitation is inadequate, parasite eggs are excreted in the faeces of infected individuals and contaminate the soil. Humans become infected through ingestion of eggs or larvae that are passed in the faeces of infected people. In addition, hookworm eggs hatch in the soil, releasing larvae that mature into a form that can actively penetrate the skin.
There is no direct person-to-person transmission, or infection from fresh faeces, because eggs passed in faeces need about three weeks to mature in the soil before they become infective. Since these worms do not multiply in the human host, reinfection occurs only as a result of contact with infective stages in the environment.
Fifteen countries in the Western Pacific Regions are endemic with soil-transmitted helmimthiases and annual or semi-annual deworming campaigns targeting children and women of childbearing age is ongoing in most of the countries for control of morbidity due to worm burden.