A soil-transmitted helminth (STH) infection is a sub-group within the group of helminth infections. It is caused specifically by those helminthes (worms) which are transmitted through soil contaminated with faecal matter and are therefore called soil-transmitted helminth (Intestinal parasitic worms) infections.
Soil-transmitted helminth (STH) infections are a major public health problem in tropical and sub-tropical countries and affect the poorest and most deprived communities. More than 1.5 billion people, or 24% of the world’s population, are infected with soil-transmitted helminth infections worldwide.STH infections are transmitted by eggs present in human faeces which in turn contaminate soil in areas where sanitation is poor.
Symptoms
People with light infections usually have no symptoms.
Heavier infections can cause diarrhoea and abdominal pain, general malaise and weakness, and impaired cognitive and physical development.
Hookworms cause chronic intestinal blood loss that can result in anaemia.
Effects on nutritional status-
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.
- 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.
The nutritional impairment caused by soil-transmitted helminths is recognized to have a significant impact on growth and physical development.
Causes
The main species that infect people are the roundworm (Ascaris lumbricoides), the whipworm (Trichuris trichiura) and hookworms (Necator americanus and Ancylostoma duodenale).
Transmission: Soil-transmitted helminths are transmitted by eggs that are passed in the faeces 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 that are 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 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 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 ineffective stages in the environment.
Diagnosis
STH can be diagnosed by examination of stool sample using Microscope for the presence of eggs.
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
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 health care provider for diagnosis.
Management
Anthelminthic medications (drugs that expel parasitic worms) are used for the treatment of helminthiasis.
WHO recommends periodic treatment with anthelminthic (deworming) medicines, without previous individual diagnosis to all at-risk people living in endemic (constant presence of disease in a population) areas. Treatment should be given once a year when the prevalence of soil-transmitted helminth infections in the community is over 20%, and twice a year when the prevalence of soil-transmitted helminth infections in the community exceeds 50%.
Prevention
The strategy for control of soil-transmitted helminth infections is to prevent and control morbidity through the periodic treatment of at-risk population living in endemic areas. People at risk are:
Preschool-aged children;
School-aged children;
Women of childbearing age (including pregnant women in the second and third trimesters and breastfeeding women)
In addition infections can be prevented by taking precautions, including:
Education on health and hygiene reduces transmission and reinfection by encouraging healthy behaviours; such as washing of hands with soap and water before handling food, wearing of protective footwear, thorough washing of raw vegetables and fruits with safe water before eating.
- Sanitary disposal of human excreta.
- Periodic deworming can be easily integrated with child health days or vitamin A supplementation programmes for preschool-aged children, or integrated with school-based health programmes.
References-
www.who.int/mediacentre/factsheets/fs366/en/
http://www.who.int/intestinal_worms/epidemiology/en/
http://www.cdc.gov/parasites/ascariasis/gen_info/faqs.html