INTRODUCTION

Soil-transmitted helminths (STHs) are one of the most important groups of infectious agents and are the responsible of serious global health issues; more than a billion people have been infected by at least one species of this group of pathogens. World wide, the most significant STHs are roundworms (Ascaris lumbricoides), whipworms (Trichuris trichiura) and hookworms (Necator americanus or Ancylostoma duodenale) and are estimated to have infected 807 million, 604 million and 576 million people, respectively. The largest numbers of STH infections occur in Sub-Saharan Africa (SSA), East Asia, China, India and South America



In the developing countries, inadequate water supply and sanitation, as well as congested living situation, together with lack of access to medical care and poor  education, make the poor specially prone to infection and disease, including STHs. In the last few years, an increasing number of international initiatives have established the goal to either reduce or to eradicate the disease load caused by STHs and other helminthic parasites common in the developing countries of the world.


Global distribution and prevalence

The STHs are more often found in children living poor sanitation, and their impact on morbidity and mortality is more severe in malnourished or undernourished populations. Over 270 million preschool-age children and over 600 million school-age children live in areas where these parasites are intensively transmitted, and are in need of treatment and preventive interventions.


CONTROL MEASURES

The world health organization (WHO) has recommended three interventions to control morbidity due to STH infections: regular drug treatment of high-risk groups for reduction of the worm burden over time, health education and sanitation supported by personal hygiene aimed at reducing soil contamination.

1. Anthelminthic treatment

Regular drug treatment represents the main approach for infection control in areas where infections are intensely transmitted, where resources for disease control are limited and where funding for sanitation is insufficient.

The selection of the delivery strategy and the frequency of treatment are based on the analysis of available epidemiological data.

WHO recommended medicines

The WHO recommends – albendazole (400 mg) and mebendazole (500 mg) –  they are effective, inexpensive and easy to be given 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.

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.

For long-term sustainability, environmental health will be required improving access to safe water and sanitation and improved hygienic behavior through health education.

2.Health education

Health and hygiene education reduces transmission and reinfection by encouraging healthy behaviors; and provision of adequate sanitation is also important but not always possible in resource-poor settings.

Educational materials (posters, leaflets, radio and video messages) have been traditionally used to transmit and disseminate health-related messages.

Reduction in the fecal contamination of soil can be achieved by recommending the use of latrines, developing self-protection from re-infection, and promoting personal/ family hygiene measures such as washing hands and proper food preparation. Frequently, in STH-endemic areas, latrines are not available or are not in sufficient numbers to meet the needs of the population.

3.Sanitation and personal hygiene

Human STHs are fecal-borne infections, and transmission occurs either directly (hand-to-mouth) or indirectly (through food and water). Sanitation in the context of economic development is the only definitive intervention that eliminates these infections.

STH infections are never a public health problem where hygiene and sanitation standards are appropriate. Improvement of sanitation standards always has a repercussion on infection and re- infection levels.

Study in the Senegal demonstrated that, despite high coverage of the program of provision of latrines, the majority of the children in a village, interviewed with a questionnaire, claimed to defecate elsewhere.

Environmental factors such as water supply for domestic and personal hygiene, sanitation and housing conditions; and other factors such as socioeconomic, demographic and health related behavior are known to influence this infection. A principal factor in maintaining endemicity of these helminths is the frequent contamination of the environment by human feces. Their transmission within the community is predominantly related to human habits with regard to eating, defecation, personal hygiene and cleanliness.

 

Other ways of prevention and control

Remote sensoring

An important emerging trend is that national governments are beginning to use this approach for designing and developing sustainable national programs. GIS/ RS has been employed by governments to plan and conduct nationwide rapid epidemiological assessments of STHs and schistosomiasis in Chad and Eritrea, and to design and implement national parasite-control programs, in both cases as part of national development programs with World Bank assistance. The results from the survey helped the government plan the country's school-based control program, and resulted in significant cost savings for the program since it identified the need to target far fewer schools than had first been anticipated. The sampling methodology proved to be substantially less expensive and more practical than traditional approaches developed without the benefit of GIS/ RS. The national survey revealed that infection was highly focal and that deworming interventions could be precisely targeted, with significant savings in financial and technical resources.

4. Control applications of GIS/RS

As recently as five years ago, applications of GIS and RS in helminthology had only been attempted for schistosomiasis and filariasis (reviewed in Brooker & Michael, 2000; Brooker, 2002). Since then studies have investigated spatial patterns of STH infection (Brooker et al., 2002c, 2003, 2004b; Saathoff et al., 2005), Loa loa (Thomson et al., 2004) and onchocerciasis (Carabin et al., 2003). These studies have focused on the use of RS data to identify ecological correlates of infection and develop statistical models of disease risk.

While these applications are attractive research objectives, the challenge remains to apply these geographic tools in the context of large-scale control programs.

The Schistosomiasis Control Initiative (SCI) is currently supporting six countries in sub-Saharan Africa to implement national control programs for schistosomiasis and STH infections, including Burkina Faso, Mali, Niger, Tanzania, Uganda and Zambia (www.schisto.org). In Uganda, where Schistosoma mansoni is widespread, GIS and RS have been employed to classify the country according to different treatment strategies. Regular chemotherapy with praziquantel and albendazole is being provided to schoolchildren and other high-risk groups (Kabatereine et al., 2005). Following WHO guidelines, the programme is classifying communities according to three strategies: (1) in communities with a high prevalence (>=50%) schoolchildren are treated every year and high risk groups, such as fishermen, are treated; (2) in communities with a moderate prevalence (>=20% and <50%) schoolchildren are treated once every two years; and (3) in communities with a low prevalence (<20%) chemotherapy are made available in health facilities for treatment of suspected cases.

The experience of SCI in Tanzania and Uganda amply demonstrates the usefulness of GIS/RS as geographic decision-making tools for implementing helminth control at both national scales and local scales.

Geographical distributions are continually updated as new epidemiological data are collected, and as intervention reduces the prevalence of infection. Analysis of the cost-effectiveness of the tools, which is germane to their long-term and sustainable use, is currently underway.

The above examples have shown how research and international programmes have led the way in developing the use of GIS/RS for directing control programs. An important emerging trend is that national governments are beginning to use this approach for designing and developing sustainable national programs. GIS/RS has been employed by national governments to plan and conduct nationwide rapid epidemiological assessments of STH and schistosomiasis in Chad (Brooker et al., 2002a) and Eritrea (Partnership for Child Development, 2003), and to design and implement national parasite control programs, in both cases as part of national development programs with World Bank assistance.

Again the sampling methodology proved substantially less expensive, and more practical, than traditional approaches developed without benefit of GIS/RS. The national survey revealed that infection was highly focal, and that deworming interventions could be precisely targeted, with significant savings in financial and technical resources.

Challenges

The effect of improved sanitation is slow to development and may take decades to achieve a measurable impact.

Often, the high costs involved prevent the provision of sanitation to the communities most in need, and sanitation does not become effective until it covers a high percentage of the population. Economic constrain poses a great challenge for prevention and control of soil transmitted helminthic infections.

Summary

Soil-transmitted helminths form one of the most important groups of infectious agents and are the cause of serious global health problems. The most important STHs are roundworms (Ascaris lumbricoides), whipworms (Trichuris trichiura) and hookworms (Necator americanus or Ancylostoma duodenale); on a global level, more than a billion people have been infected by at least one species of this group of pathogens.

This paper examined the methods for the prevention and control of soil-transmitted helminthiasis  and is based on (i) regular anthelminthic treatment, (ii) health education, (iii) sanitation and personal hygiene and (iv)other means of prevention with remote sensoring.

The reasons for the development of a control strategy based on population intervention rather than on individual treatment are discussed, as well as the costs of the prevention of STHs, although these cannot always be calculated because interventions in health education are difficult to measure. An efficient sanitation infrastructure can reduce the morbidity of STHs and eliminates the underlying cause of most poverty-related diseases and thus supports the economic development of a country.

 

REFERENCE:

1.

Global epidemiology, ecology and control of soil-transmitted helminth infections by Simon Brooker, Archie CA Clements, and Don AP Bundy.

 
2.  Prevention of Soil-transmitted Helminth Infection by Luciene Mascarini-Serra. J Glob Infect Dis. 2011 Apr-Jun; 3(2): 175–182.

 

 

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