Effects of Improved Water Supply and Sanitation on Ascariasis, Diarrhoea, Dracunculiasis, Hookworm Infection, Schistosomiasis, and Trachoma

Article excerpt

Introduction

Water and sanitation have been the subjects of considerable recent attention as a result of the declaration by the United Nations General Assembly that the 1980s were the International Drinking-Water, Supply and Sanitation Decade (IDWSSD). A major objective of this was to improve the health of populations that received the interventions. Most of the research on the health impacts of water and sanitation projects has focused on the incidences of diarrhoeral diseases, malnutrition, and mortality of young children, and evidence accumulated during the decade indicates that these rates have been reduced [22, 25]. Although it is generally believed that the rates of other diseases will decrease following improvements in water and sanitation, there have been no systematic reviews of this.

The present article reviews the health impact of water and sanitation interventions on the following: ascariasis (Ascaris lumbricoides), diarrhoeal diseases (including measures of nutritional status and child survival), dracunculiasis (Dracunculus medinensis), hookworm infection (Ancylostoma duodenale and Necator americanus), schistosomiasis (Schistosoma haematobium and S. mansoni), and trachoma (Chlamydia trachomatis). These diseases were chosen because they are widespread in developing countries, or because they constitute serious problems where they exist, or both (Table 1). All developing countries are affected by diarrhoeal diseases and ascariasis; the other four diseases are somewhat more restricted in their range, although they are all prevalent in some developing countries, except dracunculiasis, which only occurs in parts of Africa and Asia.

Table 1: Incidence and effects of selected diseases in
developing countries (excluding China)
                              Estimated number of:
                        Cases per year
                           (x [10.sup.6]   Deaths per year
Ascariasis(a)               900                 20 000
Diarrhoeal diseases(b)      875              4.6 million
Dracunculiasis(c)             4                 __f
Hookworm infection          800                 __f
Schistosomiasis(d)          200                 __f
Trachoma(e)                 500                 __g
(a-e)See ref. 96, 80, 97, 57, and 18, respectively.
(f)Usually causes debilitation rather than death.
(g)The major disability is blindness (8 million).

These diseases also illustrate the variety of mechanisms through which improved water and sanitation can promote health (Table 2). Four basic aspects were considered: sanitation (i.e., human excreta disposal), water quality, personal hygiene, and domestic hygiene. Personal hygiene refers to water used for cleaning the body, including water for the face, hands, and eyes; domestic hygiene refers to water used to keep the home clean (e.g., food, utensils, and floors). Each disease is affected by one or more of these interventions. For example, providing safe, portable sources of drinking-water will probably prevent transmission of dracunculiasis, while using larger quantities of water or personal hygiene will probably interrupt the spread of trachoma. The incidence, prevalence, and/or severity of all these diseases are reduced by water and sanitation interventions. [Tabular Data 2 Omitted]

Methods

Computer searches of articles on each of the diseases considered were carried out using the MEDLINE and MEDLINE 500 systems, which cover the period from 1966 and 1986, respectively. For schistosomiasis, an additional computer search was performed on CAB Abstracts (period, 1984-89). For hookworm infection and ascariasis, Index Medicus was searched for 1976-86, and the Science Citation Index for 1970-84. Because a thorough review of diarrhoeal diseases was published in 1986 [22], only studies published since then were sought. For trachoma, additional references were provided by a recent review [72].

References cited in the articles identified, but which were not located in the computer search, were also sought. …