Soil-transmitted helminthiasis (STH) is a type of helminth infections (helminthiasis) caused by different species of roundworms. It is caused specifically by those worms which are transmitted through soil contaminated with faecal matter and are therefore called soil-transmitted helminths. Three types of soil-transmitted helminthiasis can be distinguished: ascariasis, hookworm disease and trichuriasis. These three types of infection are therefore caused by the large roundworm A. lumbricoides; the hookworms Necator americanus or Ancyclostoma duodenale; and by the whipworm Trichuris trichiura respectively.