Environmental Health Engineering in the Tropics

Water, Sanitation and Disease Control

Sandy Cairncross, Sir Richard Feachem

• Publisher: Routledge
• Year: 2018
• Print ISBN: 9781844071906
• eBook ISBN: 9781134665860
• Edition: 3
• Topic: Medicine
• Subtopic: Ecology

This fully updated third edition of the classic text, widely cited as the most important and useful book for health engineering and disease prevention, describes infectious diseases in tropical and developing countries, and the effective measures that may be used against them.

The infections described include the diarrhoeal diseases, the common gut worms, Guinea worm, schistosomiasis, malaria, Bancroftian filariasis and other mosquito-borne infections. The environmental interventions that receive most attention are domestic water supplies and improved excreta disposal. Appropriate technology for these interventions, and also their impact on infectious diseases, are documented in detail.

This third edition includes new sections on arsenic in groundwater supplies and arsenic removal technologies, and new material in most chapters, including water supplies in developing countries and surface water drainage.

Part I

Health and pollution

Chapter 1

Engineering and infectious disease

1.1Introduction

Environmental health engineering concerns engineering methods for the improvement of the health of the population. In practice it has come to focus especially upon domestic water supplies and excreta disposal facilities. Other engineering interventions, such as drainage, housing and irrigation scheme design, are also relevant in the tropics. However their impact on public health is generally smaller, less certain and less cost-effective than investments in water and sanitation (Cairncross et al. 2003).

One is unlikely to succeed in improving public health unless one understands it, and in the tropics this understanding must apply chiefly to the infectious diseases. Although most of these have now been brought under control or even eliminated in the industrialised countries, they are still the principal cause of ill-health among the world’s poor.

An infectious disease is one which can be transmitted from one person to another or, sometimes, to or from an animal. All infectious diseases are caused by living micro-organisms, such as bacteria, viruses or parasitic worms, and a disease is transmitted by the passing of these organisms from one person’s body to another.

During the transmission process, the organisms may be exposed to the environment, and their passage to the body of a new victim is then vulnerable to changes in the environment. Environmental health engineering seeks to modify the human environment in such a way to prevent or reduce the transmission of infectious diseases.

Being infected is not the same as being ill. Very often, the section of the population most involved in transmitting an infection shows little or no sign of disease; conversely, people who are seriously ill with the disease may be of little or no importance in its transmission. For example, when a cholera epidemic sweeps through a community, those who show signs of cholera are only a small minority of those who are infected with the disease. Anyone who is infected, whether ill or not, is likely to pass it on to others.

For the environmental health engineer, it is convenient to start by classifying the relevant infectious diseases into categories which relate to the various aspects of the environment which can be altered. The conventional generic or biological taxonomy¹ of disease classifies them according to the nature of their pathogens² – the organisms which cause them. That classification system is unhelpful to environmental interventions. For instance, smallpox is grouped with hepatitis, and filariasis³ is grouped with Guinea worm. In this chapter, infectious diseases are grouped in a way which is more helpful to the environmental health worker.

1.2Water-related infections

A water-related disease is one which is related somehow to water or to impurities in water. In low and middle income countries it is usually the infectious water-related diseases which are of prime importance; these are the subject of this chapter. We distinguish the infectious water-related diseases from those related to some chemical property of the water. Damage to the teeth and bones, for instance, is associated in some countries with high fluoride levels; this non-infectious type of water-related disease is dealt with in Chapter 2.

Classification of transmission mechanisms

Before we can classify the water-related infections, we must define the four distinct types of water-related route by which a disease may be transmitted from one person to another. These are shown in Table 1.1, and are related there to the environmental strategies for disease control which are appropriate to each. The four routes are described below.

Table 1.1The four types of water-related transmission route for infections and the preventive strategies appropriate to each

Transmission route	Preventive strategies
Water-borne	Improve quality of drinking water Prevent casual use of unprotected sources
Water-washed (or water-scarce)	Increase quantity of water available Improve accessibility and reliability of domestic water supply Improve hygiene
Water-based	Reduce need for contact with infected water Control population of aquatic hosts (e.g. snails) Reduce contamination of surface waters*
Water-related insect vector	Improve surface water management Destroy breeding sites of insects Reduce need to visit breeding sites Use mosquito netting

* The preventive strategies appropriate to the water-based worms depend on the precise life cycle of each species.

1.Water-borne route

Truly water-borne transmission occurs when the pathogen is in water which is drunk by a person who may then become infected. Potentially water-borne diseases include the classical infections, notably cholera and typhoid, but also include a wide range of other diseases, such as infectious hepatitis, diarrhoeas and dysenteries.

The term ‘water-borne disease’ has been, and still is, greatly abused so that it has become almost synonymous with ‘water-related disease’. It is essential to use the term water-borne only in the strict sense defined here.

Another source of misunderstanding has been the assumption that, because a disease is labelled water-borne this describes its usual, or even its only means of transmission. The preoccupation with strictly water-borne transmission has its origins in the dramatic water-borne epidemics of cholera and typhoid which occurred in some European towns in the nineteenth and early twentieth century, and were largely caused by urban water supplies with inadequate treatment facilities. Similar epidemics sometimes occur in tropical towns today, but all water-borne diseases can also be transmitted by any route which permits faecal material to pass into the mouth (a ‘faecal–oral’ route). Water-borne transmission is merely the special case of ingesting faecal material in water, and any disease which can be water-borne can also be transmitted by other faecal–oral routes.

2.Water-washed route

There are many infections of the intestinal tract and of the skin which, especially in the tropics, may be significantly reduced following improvements in domestic and personal hygiene. These improvements in hygiene often result from increased availability of water allowing the use of increased volumes of water for hygienic purposes. Their transmission can be described as ‘water-washed’; it depends on the quantity of water used, rather than the quality. The relevance of water to these diseases is that it is an aid to hygiene and cleanliness, and its quality is relatively unimportant. A water-washed disease may be formally defined as one whose transmission will be reduced following an increase in the volume of water used for hygienic purposes, irrespective of the quality of that water.

Water-washed diseases are of three main types. First, there are infections of the intestinal tract, such as diarrhoeal diseases, which are important causes of serious illness and death especially among young children in poor countries. These include cholera, bacillary dysentery and other diseases previously mentioned under the water-borne route. These di...

Table of contents

• Cover
• Half Title
• Series Information
• Title Page
• Copyright Page
• Contents
• Preface to the first edition: environmental health engineering and poverty
• Preface to the second edition
• Preface to the third edition
• Acknowledgements
• Part I Health and pollution
• Part II Water supply
• Part III Excreta and refuse: Treatment, disposal and re-use
• Part IV Environmental modifications and vector-borne diseases
• Appendix A: Biological classification conventions
• Appendix B: Glossary
• Appendix C: Checklist of water-related and excreta-related diseases
• Appendix D: A brief primer on urban mosquito control
• Appendix E: Units
• Index