Environmental Engineering Reference
In-Depth Information
To these may be added three more:
5.
Inhalation of water aerosols contaminated by a pathogenic agent
.This
could include
Legionella pneumophila
, the etiologic agent of legionellosis
and Pontiac fever.
6.
Consumption of water-based foods derived from contaminated water
.Sick-
ness might be related, for example, to ingestion of raw shellfish containing
Vibrio vulnificus
or
V. parahemolyticus
, both causative agents of diarrheal
diseases.
7.
Consumption of foods that have had contact with contaminated water at
some stage of production
. Sickness results from microbial contamination
during production/preparation (e.g., irrigation, washing, and preservation)
of food such as leafy vegetables.
Many disease-producing viruses and bacteria have been identified in this
connection, and the protozoan,
Cyclospora cayetanensis
, etiologic agent of a
diarrheal disease, cyclosporiasis, with pathology resembling that of cryptosporid-
iosis, has been identified in imported raspberries and lettuce from South American
countries.
3
At this juncture, it is recommended that the reader consult the definition of
terms in Chapter 2 in order to appreciate textural issues. Most definitions of
the phrase “communicable disease” emphasize the involvement of an identifiable
pathogenic agent. With any communicable disease, there is the need to transmit
or communicate an infectious agent to a host by means of a vector or vehicle or
person-to-person contact. Continuous propagation of the communicable disease
within members of a population requires that the infectious agent be able to exit
the diseased individual and find access to a healthy person. One definition of
communicable disease appears in the list of definitions given in Chapter 3 and
includes “toxic products” of infectious agents as an instrument of communicable
diseases. Biological-based toxins alone have rarely been found to be the cause
of a water-transmitted disease. However, such toxins are a potential weapon for
terrorists and, notwithstanding the minimal chance of success, are an anticipated
threat to water supplies.
Ingestion of chemical contaminants in water may cause acute and chronic
forms of toxicity leading to the development of noncommunicable diseases in
individuals. Biological agents are the cause of infectious (communicable) diseases
that may or may not be contagious.
Control of Source (Agent Factors)
Certain sources of disease agents are noted in Figure 1.1. Gerstman
4
defines an
agent as a biological, chemical, or physical factor whose presence or absence in
varying amounts is required for the occurrence of a disease; a form of necessary
factor. Gerstman identified several types of factors of varying essentiality in the
propagation of a communicable disease. The agent is a necessary factor, that is,
its presence in the host is required to produce a disease although its presence
