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close this bookWater and Sanitation Technologies: A Trainer's Manual (Peace Corps, 1985)
close this folderSessions
close this folderSession 9 - Introduction to environmental sanitation
View the document(introduction...)
View the documentAttachment 9A: Water-related diseases



Two hours


* Discuss the relationship between the environment and disease through an understanding of the disease cycle

* Identify the causes of water related disease, common means of transmission, preventative measures, and general treatments

* Define several important epidemiological concepts


Rural Water and Sanitation Projects; USAID, pp. 11-27

Sanitation Without Water; Winblad/Kilama, Chapter 1

Small Excreta Disposal Systems; Ross Institute, Chapter 1

Attachment 9-A, "Water-Related Diseases"


Newsprint and felt-tip pens, copies of Attachment 9-A for all trainees


One or more trainers

Trainer Introduction

This session is designed to deal primarily with water-related and excreta-related disease. Trainers should be quite familiar with the subject matter. The reading assignment should be read by the trainees prior to the session.


Step 1

5 minutes

Present the objectives and format for the session.

Trainer Note

Acknowledge the fact that this session may produce some anxiety in the trainees when they think about life in third world countries. Point out that exposure to disease is unavoidable as Peace Corps Volunteers. However, in actuality, the environments they will live in are generally wholesome and the diseases that are prevalent there are recognized, understood, and controllable. Mention that in contrast, many of the diseases prevalent in the western world, such as cancer, are not so recognizable, understood, or easily controlled.

Step 2

10 minutes

Trainees brainstorm a list of environmental factors that facilitate disease transmission.

Trainer Note

Disease transmission occurs directly, such as in colds, or sexually transmitted disease, and indirectly, such as dysentery transmitted through bad water.
Facilitate the discussion and list responses on newsprint. Some possible answers are:

lack of education
climate and topography
insects, animals
unsanitary facilities
population density
contaminated water, air or soil

Emphasize the interrelationship between the environment and disease transmission. The study of infectious disease is, in fact, an ecological one, because of the interrelationship between organisms and their environment. This concept is important because it leads one to study what organisms (or infectious agents) need to live, propagate, and survive in their environment. This knowledge can lead to a change in environment which then leads to disease prevention.

Step 3

15 minutes

Discuss ways to prevent disease transmission

Trainer Note

Focus the discussion on these two primary areas:

1) Interrupting the cycle of infection on one of two levels:

- Community, i.e., eliminating breeding areas for mosquitos in the case of malaria, or banning swimming in snail infected waters in the case of shisto

- Personally, i.e., boiling drinking water, wearing shoes, using latrines, washing hands before eating, washing vegetables and fruit.

2) Resistance measures such as:

- Vaccinations
- Prophylaxis
- Self care through proper nutrition, adequate sleep, stress management, etc.
- Early diagnosis and treatment
- Avoidance of situations which may compromise immunity
- Natural immunity which all people have. However, when entering a foreign environment the natural immune system will be challenged.

Step 4

30 minutes

Lecturette on the Disease Cycle and Chain of Infection.

Trainer Note

Begin by listing the three primary living factors in a disease cycle: host, infectious agent, and vector or vehicle. Explain the relationship between the three factors and the following types of disease cycles:

Host and Infectious Agent: diseases which are transferred from person to person without intervention: measles, scabies, sexually transmitted disease, colds:

Host and Infectious Agent

Host, Infectious Agent, and Vector or Vehicles: diseases which are transmitted by, and often perpetuated in, animal carriers: malaria, filariasis, yellow fever, epidemic typhus

Host, Infectious Agent, and Vector or Vehicles

Next, explain each of the following terms, giving examples of each:

Infectious Agents: small organism or virus living in or on, and at the expense of, a large organism. The number of organisms necessary to initiate disease varies according to its virulence and the resistance of host. Infectious agents vary greatly in the length of time they live within their host, or outside in the environment. They also use various pathways to host.

Examples include:

- viruses as in hepatitis (cannot be fought with medication)
- bacteria as in typhoid or gonorrhea
- parasites such as protozoa as in amoeba, giardia; and helminths as in ascaris, ankylostoma (hookworm)
- fungus, fleas, and lice

Vector: the living transporter and transmitter of the causative agent of disease. Examples are flies, mosquitoes, ticks, cockroaches, lice, rats, bats, snails and dogs.

Vectors use various methods to transmit disease: mosquitoes inject into bloodstream, flies deposit pathogenic organisms on food, dogs and rats bite, etc.

There are two types of vectors:

1) Mechanical, i.e., directly transmits the disease by crawling or flying, such as insects like flies, and does not require propagation or development of an organism.

2) Biological, i.e., propagation or multiplication must take place before the vector can transmit the infectious form of the agent, such as the female mosquito in the case of malaria.

Vehicle: an inanimate material or object which serves as an intermediate means by which an infectious agent is transported. Examples include: toys, clothes, utensils, water, food, blood products.

Host: any living animal or plant affording subsistence and, often, lodging to an infectious agent under natural conditions. Examples include people, animals, and insects.
A primary host is a carrier in/on which the organism attains maturity or carries out sexual cycle. The secondary host is a carrier in/on which the organism is in larval stage or carries out asexual development. A transport host is a carrier in which an organism remains alive but does not undergo development. There is often a varied interval of time between when an infectious agent enters a host and when symptoms of disease appear. It can do many things in a host: die quickly, live without causing harm, cause disease, or kill the host. Various factors influence how infected the host will become. The host may have natural immunity to an organism because of previous exposure, or because of generally good health and nutrition. A host may acquire immunity through vaccines or prophylaxis. Lastly, the virulence of the organisms will influence its effect on the host.

Reservoir: a place where an infectious agent normally lives and multiplies, on which it depends primarily for its survival, and reproduces itself in such a manner that it can be transmitted to a susceptible host. Examples are people, animals, birds, reptiles, and insects. A reservoir may carry a disease for varied lengths of time, often without showing symptoms.

Lastly, briefly explain a general Chain of Infection such as the one shown below.

General chain of infection

Step 5

10 minutes

Briefly define the four water-related disease categories: waterborne, water hygiene, water contact, water-related insect vector.

Step 6

40 minutes

Handout Attachment 9-A. Give presentations on four diseases, one from each water-related disease category.

Trainer Note

Discuss each disease, explaining the chain of infection and means of transmission, preventative measures, and general treatments. Use the information provided in the attachment and from the reading assignment in Rural Water and Sanitation Projects.

Step 7

10 minutes

Review the objectives and conclude the session.

Trainer Note

Conclude by pointing out that communicable diseases, such as those discussed during this session, are a part of life in third world countries. Consequently, such diseases are a part of all Peace Corps Volunteers' lives. However, as pointed out in Step 1, these diseases are for the most part recognized, understood, and controllable. In fact, many Volunteers around the world are working hard to prevent, control, or even eradicate these diseases.