The soil-transmitted helminths (also called geohelminths) are a group of

intestinal parasite An intestinal parasite infection is a condition in which a parasite infects the gastro-intestinal tract of humans and other animals. Such parasites can live anywhere in the body, but most prefer the intestinal wall. Routes of exposure and inf ...

s belonging to the

phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...

Nematoda The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitism, parasitic. Parasitic ...

that are transmitted primarily through contaminated soil. They are so called because they have a direct

life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from conception to reproduction *Life-cycle hypothesis, in economics *Erikson's stages of psy ...

which requires no

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

s or vectors, and the

parasitic infection A parasitic disease, also known as parasitosis, is an infectious disease caused by parasites. Parasites are organisms which derive sustenance from its host while causing it harm. The study of parasites and parasitic diseases is known as parasitolog ...

occurs through faecal contamination of soil, foodstuffs and water supplies. The adult forms are essentially

parasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

of humans, causing

soil-transmitted helminthiasis Soil-transmitted helminthiasis is a type of worm infection (helminthiasis) caused by different species of roundworms. It is caused specifically by worms transmitted through soil contaminated with faecal matter and are known as soil-transmitted ...

(STH), but also infect

domesticated Domestication is a multi-generational mutualistic relationship in which an animal species, such as humans or leafcutter ants, takes over control and care of another species, such as sheep or fungi, to obtain from them a steady supply of reso ...

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

. The juveniles are the infective forms and they undergo tissue-migratory stages during which they invade vital organs such as

lungs The lungs are the primary organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the backbone on either side of the heart. Their function in the respiratory syste ...

and

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

. 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.

Species

Soil-transmitted helminths are typically from the following

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

s, namely: * Roundworms (family

Ascarididae The Ascarididae are a family of the large intestinal roundworms. Members of the family are intestinal parasites, infecting all classes of vertebrates. It includes a number of genera,Anderson RC (2000)''Nematode Parasites of Vertebrates. Their De ...

), e.g. ''

Ascaris lumbricoides ''Ascaris lumbricoides'' is a large parasitic worm, parasitic Nematoda, roundworm of the genus ''Ascaris.'' It is the most common parasitic worm in humans. An estimated 807 million–1.2 billion people are infected with ''Ascaris lumbricoides'' ...

'' * Whipworms (family

Trichuridae The nematode, roundworm family (biology), family Trichuridae includes the type genus ''Trichuris'' and some less widely known members. They are (after the abolishment of the artificial "Adenophorea" assemblage) placed in subclass Dorylaimia of th ...

), e.g. ''

Trichuris trichiura ''Trichuris trichiura, Trichocephalus trichiuris'' or whipworm, is a parasitic roundworm (a type of helminth) that causes trichuriasis (a type of helminthiasis which is one of the neglected tropical diseases) when it infects a human large inte ...

'' * Hookworms (family

Ancylostomatidae The Ancylostomatidae are a family of worms that includes the hookworm Hookworms are Gastrointestinal tract, intestinal, Hematophagy, blood-feeding, parasitic Nematode, roundworms that cause types of infection known as helminthiases. Hookworm i ...

), e.g. ''

Ancylostoma duodenale ''Ancylostoma duodenale'' is a species of the roundworm genus '' Ancylostoma''. It is a parasitic nematode worm and commonly known as the Old World hookworm. It lives in the small intestine especially the jejunum of definitive hosts, generally ...

'' and ''

Necator americanus ''Necator americanus'' is a species of hookworm (a type of helminth) commonly known as the New World hookworm. Like other hookworms, it is a member of the phylum Nematoda. It is an obligatory parasitic nematode that lives in the small intestin ...

'' * Threadworms (family

Strongyloididae Strongyloididae is a family of nematodes belonging to the order Rhabditida Rhabditida is an order of free-living, parasitic and microbivorous nematodes living in soil. The Cephalobidae, Panagrolaimidae, Steinernematidae, and Strongyloid ...

), e.g. ''

Strongyloides stercoralis ''Strongyloides stercoralis'' is a human pathogenic parasitic roundworm causing the disease strongyloidiasis. Its common name in the US is threadworm. In the UK and Australia, however, the term ''threadworm'' can also refer to nematodes of t ...

Diseases

Soil-transmitted helminthiasis

Soil-transmitted helminthiasis is a collective name for the diseases caused by ascaris, whipworm and hookworms in humans. It includes species-specific diseases such as *

Ascariasis Ascariasis is a disease caused by the parasitic roundworm ''Ascaris lumbricoides''. Infections have no symptoms in more than 85% of cases, especially if the number of worms is small. Symptoms increase with the number of worms present and may in ...

, which is caused by ''

'' *

Hookworm disease Hookworm infection is an infection by a type of helminths, intestinal parasite known as a hookworm. Initially, itching and a rash may occur at the site of infection. Those only affected by a few worms may show no symptoms. Those infected by many ...

s (

ancylostomiasis Ancylostomiasis is a hookworm disease caused by infection with '' Ancylostoma'' hookworms. The name is derived from Greek ancylos αγκύλος "crooked, bent" and stoma στόμα "mouth". Ancylostomiasis is also known as miner's anaemia, tu ...

and

necatoriasis Necatoriasis is the condition of infection by '' Necator'' hookworms, such as ''Necator americanus''. This hookworm infection is a type of helminthiasis (infection) which is a type of neglected tropical disease. Signs and symptoms When adult wo ...

), which are caused by ''

'' and ''

'' *

Trichuriasis Trichuriasis, also known as whipworm infection, is an infection by the parasitic worm '' Trichuris trichiura'' (whipworm). If the infection is only with a few worms, there are often no symptoms. In those who are infected with many worms, there ...

, which is caused by ''

'' Soil-transmitted helminthiasis is classified as one of the

neglected tropical diseases Neglected tropical diseases (NTDs) are a diverse group of tropical infections that are common in low-income populations in developing regions of Africa, Asia, and the Americas. They are caused by a variety of pathogens, such as viruses, bacteri ...

projected to be controlled/eradicated by 2020 through the ''

London Declaration on Neglected Tropical Diseases The London Declaration on Neglected Tropical Diseases was a collaborative disease eradication programme launched on 30 January 2012 in London. It was inspired by the World Health Organization roadmap to eradicate or prevent transmission for neglec ...

''.

Strongyloidiasis

This is caused by ''

''. 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

pet A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive/ cute appearances, inte ...

s. But there is an emerging hyperinfection syndrome caused by ''S. stercoralis'', which exhibits a high

mortality rate Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular Statistical population, population, scaled to the size of that population, per unit of time. Mortality rate is typically ...

(15% to 87%).

General impact

Geohelminth infection is a major health problem particularly in

rural areas In general, a rural area or a countryside is a geographic area that is located outside towns and cities. Typical rural areas have a low population density and small settlements. Agricultural areas and areas with forestry are typically descri ...

developing countries A developing country is a sovereign state with a less-developed Secondary sector of the economy, industrial base and a lower Human Development Index (HDI) relative to developed countries. However, this definition is not universally agreed upon. ...

Subsaharan Africa Sub-Saharan Africa is the area and regions of the continent of Africa that lie south of the Sahara. These include Central Africa, East Africa, Southern Africa, and West Africa. Geopolitically, in addition to the African countries and territ ...

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

and other

Southeast Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...

n countries. It is an important cause of

morbidity A disease is a particular abnormal condition that adversely affects the structure or function of all or part of an organism and is not immediately due to any external injury. Diseases are often known to be medical conditions that are asso ...

in school age children who harbour the highest intensity of worm infestation. Some of the significant morbidity attributed to intestinal

helminthiasis Helminthiasis, also known as worm infection, is any macroparasite, macroparasitic disease of humans and other animals in which a part of the body is infected with parasitism, parasitic worms, known as helminths. There are numerous species of the ...

are

malnutrition Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is a deficiency, excess, or imbalance of energy, protein and other nutrients which adversely affects the body's tissues a ...

growth retardation A delayed milestone, which is also known as a developmental delay, refers to a situation where a child does not reach a particular developmental milestone at the expected age. Developmental milestones refer to a collection of indicators that a chil ...

anaemia Anemia (also spelt anaemia in British English) is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin availab ...

vitamin A deficiency Vitamin A deficiency (VAD) or hypovitaminosis A is a lack of vitamin A in blood and tissues. It is common in poorer countries, especially among children and women of reproductive age, but is rarely seen in more developed countries. Vitamin A pla ...

and impaired intellectual performance.

Control activities

The World Health Organization is promoting the control of soil transmitted helminthiasis with large scale, regular distribution of anthelminthics (albendazole or mebendazole) to the population groups more at risk of morbidity (children and women of reproductive age). The number of school-age children treated with PC has progressed steadily from less than 120 million in 2008 to over 450 million in 2018 and is in continuous espansion.

References

External links

WHO information page

USAID's Soil-Transmitted Helminth Program

World Health Organisation (WHO) topic page on helminthiasis
{{DEFAULTSORT:Soil-transmitted helminths

Soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

Tropical diseases Intestinal infectious diseases Parasitic diseases Helminthiases Foodborne illnesses Conditions diagnosed by stool test