The soil-transmitted helminths (also called geohelminths) are a group of intestinal parasites belonging to the classNematoda that are transmitted primarily through contaminated soil. They are so called because they have a direct life cycle which requires no intermediate hosts or vectors, and the parasitic infection occurs through faecal contamination of soil, foodstuffs and water supplies. The adult forms are essentially parasites of humans, causing soil-transmitted helminthiasis (SHT), but also infect domesticatedmammals. The juveniles are the infective forms and they undergo tissue-migratory stages during which they invade vital organs such as lungs and liver. Thus the disease manifestations can be both local and systemic. The geohelminths together present an enormous infection burden on humanity, amounting to 135,000 deaths every year, and persistent infection of more than two billion people.
This is caused by Strongyloides stercoralis. Even though the disease is principally a soil-transmitted helminthiasis, the infection being mediated through contaminated soil, it is however generally omitted in clinical practices and control programmes because of its (allegedly) relatively less significant influence on health and socio-economic conditions. Also it is not restricted to humans, as it is common in pets. But there is an emerging hyperinfection syndrome caused by S. stercoralis, which exhibits a high mortality rate (15% to 87%).
^In the UK and Australia, however, the term threadworm can also refer to nematodes of the genus Enterobius, otherwise known as pinworms. Vide Vanderkooi, M. (2000). Village Medical Manual (5th ed.). Pasadena: William Carey Library. ISBN0878087788.
^Marcos LA, Terashima A, Dupont HL, Gotuzzo E (2013). "Strongyloides hyperinfection syndrome: an emerging global infectious disease". Trans R Soc Trop Med Hyg102 (4): 314–318. doi:10.1016/j.trstmh.2008.01.020. PMID18321548.