Soil-transmitted helminthiasis
Soil-transmitted helminthiasis is a type of helminth infection caused by different species of roundworms which are transmitted through soil contaminated with fecal matter.
Three types of soil-transmitted helminthiasis can be distinguished:
- ascaris
- hookworm infection
- whipworm infection
Please find more information on this disease in the text below or watch the expert interview:
Soil transmitted helminthiasis
What is the disease?
How dangerous is soil-transmitted helminthiasis?
People with soil-transmitted helminthiasis suffer from abdominal pain, diarrhea or blockage. Its sequelae are retarded growth and mental as well as cognitive development.
Latest estimates indicate that the total annual death toll which is directly attributable to soil-transmitted helminthiasis is as high as 135,000.
The death toll due to the malnutrition link is likely to be much higher.
However, safe and effective medicines are available to control infection.
Who is at risk?
Soil-transmitted helminth infections are among the most common infections worldwide.
All Persons living in or travelling to areas with warm and humid climates and poor sanitation and hygiene are at risk if soil contaminated with human feces enters their mouths or if they eat vegetables or fruit that have not been carefully washed, peeled or cooked.
How many people are affected by soil-transmitted helminthiasis?
Soil-transmitted helminthiasis has become the most common parasitic disease of humans worldwide. More than 1.5 billion people, or 24 percent of the world’s population, are infected with soil-transmitted helminth infections worldwide.
Over 267 million preschool-age children and over 568 million school-age children live in areas where these parasites are intensively transmitted.
Where is soil-transmitted helminthiasis found?
Soil-transmitted helminthiasis occurs worldwide in warm and humid climates, where sanitation and hygiene are poor, including in temperate zones during warmer months.
The greatest numbers occur in sub-Saharan Africa, the Americas, China and East Asia.
How do people get soil-transmitted helminthiasis?
Soil-transmitted helminthiasis is caused mainly by ingesting infective eggs. This can happen when hands or fingers with contaminated dirt on them are put in the mouth or by consuming vegetables or fruits that have not been carefully cooked, washed or peeled.
Helminths live in the intestine and their eggs are passed in the feces of infected persons. If the infected person defecates outside, or if the feces of an infected person are used as fertilizer, then eggs are deposited on the soil. There they can mature into a form that is infective.
In addition, hookworm eggs hatch in the soil, releasing larvae that mature into a form that can actively penetrate the skin. People become infected with hookworm primarily by walking barefoot on the contaminated soil.
What are the signs and symptoms of soil-transmitted helminthiasis?
People with only few worms and therefore infections of light intensity usually do not suffer from the infection.
Heavier infections can cause a range of symptoms like:
- diarrhea and abdominal pain
- malnutrition
- general malaise and weakness
- impaired growth and physical development
Itching and a localized rash are often the first signs of infection with hookworms. These symptoms occur when the larvae penetrate the skin.
How is the disease developing?
Soil-transmitted helminths impair the nutritional status of the people they infect in multiple ways:
- the worms feed on host tissues, including blood, which leads to a loss of iron and protein
- hookworms in addition cause chronic intestinal blood loss that can result in anaemia
- the worms increase malabsorption of nutrients. In addition, roundworm may possibly compete for vitamin A in the intestine
- some soil-transmitted helminths also cause loss of appetite and, therefore, a reduction of nutritional intake and physical fitness. In particular, T. trichiura can cause diarrhoea and dysentery
When children are continuously infected by many worms, they can suffer from retarded growth and mental as well as cognitive development.
How is soil-transmitted helminthiasis diagnosed?
Health care providers can diagnose soil-transmitted helminthiasis by taking a stool sample and using a microscope to look for the presence of eggs.
Some people notice infection when a worm is passed in their stool or is coughed up. If this happens, bring in the worm specimen to your health care provider for diagnosis.
How is soil-transmitted helminthiasis treated?
The WHO recommended medicines – albendazole (400 mg) and mebendazole (500 mg) – are effective, inexpensive and easy to administer even by non-medical personnel. They have been through extensive safety testing and have been used in millions of people with few and minor side-effects.
Infections are generally treated for 1-3 days.
Both albendazole and mebendazole are donated to national ministries of health through WHO in all endemic countries for the treatment of all children of school age.
In developing countries, groups at higher risk for soil-transmitted helminth infections are often treated without a prior stool examination. Treating in this way is called preventive treatment.
The high-risk groups identified by the World Health Organization are preschool and school-age children, women of childbearing age, including pregnant women in the 2nd and 3rd trimesters and lactating women, and adults in occupations where there is a high risk of heavy infections.
School-age children are often treated through school-health programs and preschool children and pregnant women at visits to health clinics.
How can I prevent infection?
- avoid contact with soil that may be contaminated with human feces, including with human fecal matter ("night soil") used to fertilize crops
- wash your hands with soap and warm water before handling food
- teach children the importance of washing hands to prevent infection
- wash, peel, or cook all raw vegetables and fruits before eating, particularly those that have been grown in soil that has been fertilized with manure
Transmission of infection to others can be prevented by
- not defecating outdoors
- effective sewage disposal systems.
How is soil-transmitted helminthiasis transmitted?
Soil-transmitted helminths are transmitted by eggs that are passed in the feces of infected people. Adult worms live in the intestine where they produce thousands of eggs each day. In areas that lack adequate sanitation, these eggs contaminate the soil.
Transmission can happen in several ways:
- eggs attached to vegetables are ingested when the vegetables are not carefully cooked, washed or peeled
- eggs are ingested from contaminated water sources
- eggs are ingested by children who play in the contaminated soil and then put their hands in their mouths without washing them
In addition, hookworm eggs hatch in the soil, releasing larvae that mature into a form that can actively penetrate the skin. People become infected with hookworm primarily by walking barefoot on the contaminated soil.
There is no direct person-to-person transmission, or infection from fresh feces, because eggs passed in feces need about three weeks to mature in the soil before they become infective.
Since these worms do not multiply in the human host, re-infection occurs only as a result of contact with infective stages in the environment.
How can soil-transmitted helminthiasis be controlled?
Control is based on:
- periodical deworming to eliminate infecting worms
- health education to prevent re-infection
- improved sanitation to reduce soil contamination with infective eggs.
What are the difficulties and challenges in combating soil-transmitted helminthiasis?
- maintaining and consolidating advances made in disease control
- enhancing access to diagnosis and treatment for millions of infected people
- developing better diagnostics, medication with less side effects especially for children and a vaccine to prevent infection
- increasing awareness of the disease among both the vulnerable population and all decision-makers who have an impact on the elimination of the disease
- underfunding of vector control and decentralization of facilities and manpower
What programs exist against Soil-transmitted helminthiasis?
The soil-transmitted helminths are sometimes treated through mass drug administrations. Since the drugs used are safe and inexpensive or donated, entire risk groups are offered preventive treatment.
Albendazole is donated by GlaxoSmithKline
Mebendazole is donated by Johnson & Johnson)
Mass drug administrations are conducted periodically, commonly with drug distributors who go door- to-door.
Multiple neglected tropical diseases are often treated simultaneously using MDAs.
In 2001, delegates at the World Health Assembly unanimously en-dorsed a resolution (WHA54.19) urging endemic countries to start tackling worms, specifically schistosomiasis and soil-transmitted helminths.
The strategy for control of soil-transmitted helminth infections is to control morbidity through the periodic treatment of at-risk people living in endemic areas. People at risk are:
- preschool children and school-age children
- women of childbearing age including pregnant women in
the second and third trimesters and breastfeeding women - adults in certain high-risk occupations
WHO recommends periodic deworming through medicinal treat-ment without previous individual diagnosis to all at-risk people living in endemic areas.
Treatment should be given once a year when the baseline prevalence of soil-transmitted helminth infections in the community is over 20%, and twice a year when the prevalence of soil-transmitted hel-minth infections in the community is over 50%. This intervention reduces morbidity by reducing the worm burden.
In addition:
- health and hygiene education reduces transmission and reinfection by encouraging healthy behavior
- provision of adequate sanitation is also important but not always possible in resource-poor settings
In 2016, over 385 million school-aged children were treated with anthelminthic medicines in endemic countries, corresponding to 68% of all children at risk.
Schools provide a particularly good entry point for deworming activities, as they allow the easy provision of the health and hygiene education component, such as promotion of handwashing and improved sanitation.
In 2017 WHO published an updated, evidence-informed guideline on the regular large-scale treatment of people against soil-transmitted helminths. The guideline endorses the current practice in areas endemic for the three main worm species that cause the disease.
The global target is to eliminate morbidity due to soil-transmitted helminthiases in children by 2020. This will be obtained by regularly treating at least 75 percent of the children in endemic areas which is an estimated 836 million in 2016.
currently no activities
What is the societal burden of soil-transmitted helminthiasis?
Soil-transmitted helminthiasis is often associated with malnutrition in children as it worsens their nutritional status in multiple ways.
The worms can induce intestinal bleeding, competition for nutrients, frequent anaemia and diarrhoea. Soil-transmitted helminths can also cause loss of appetite.
These nutritional effects can have a significant impact on the mental and physical development of children.
In endemic countries, communities remain suppressed due to mal-nourishment, cognitive disability and physical weaknesses as a result of heavy infections.