Environmental Engineering Reference
In-Depth Information
viruses and their effects on hosts are becoming better understood, resulting in
recognition of the pathogenicity of viruses thought to be innocuous.
Data on infectious doses for many important environmentally transmitted dis-
eases are lacking. Obtaining estimates of infectious doses is time consuming,
animal or human subject intensive, and costly. An indication of the difficulty
involved may be imagined in economics of testing for the effect of chemicals as
given by Kennedy:
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“A typical chronic toxicology test on compound X, done
to meet a regulatory requirement with an adequate number of animals and an
appropriate test protocol, costs $250,000 to 300,000” and requires 2 to 3 or more
years to complete.
Information concerning the
acute
effect of ingestion of toxic substances is
available in toxicology texts.
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Summary of Characteristics and Control
of Water- and Foodborne Diseases
In view of the fact that water- and foodborne diseases result in discomfort, disabil-
ity, or even death, a better understanding of their source, method of transmission,
control, and prevention is desirable. Although not mutually inclusive throughout,
several of the infections transmitted by contaminated food and water are caused
by the same pathogenic agents. The primary focus of attack is the gastrointestinal
tract.
Special attention should be paid the subject of gastroenteritis. It is a vaguely
understood disease with a complex epidemiology, often without a known causal
pathogen or chemical instigator. Three types of gastroenteritis may be distin-
guished by the pathological response to the presence of an infectious agent:
(1) noninflammatory, (2) inflammatory, and (3) invasive (Table 1.3).
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Ye t , d i f f e r -
ent forms of gastroenteritis typically display common symptoms such as watery
diarrhea, vomiting, intestinal and stomach cramps, and muscular aches, all of
which create a nausea in the victim. The purging of the gastrointestinal tract that
takes place removes or inactivates the normal barriers to infection and changes
the unshielded epithelium that alters the host defenses, causing malabsorption and
nutrient loss. The severity of the symptoms somewhat characterizes the nature
of its etiology as do the complications that accompany protracted illnesses.
There are acute and chronic forms of gastrointestinal diseases. The number of
cases worldwide of gastrointestinal illnesses are estimated to be from 6 billion
to 60 billion of which over 2 million directly result in death.
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Acute forms of
gastroenteritis outbreaks in countries of the world have a storied history, some
of which are noted elsewhere in this chapter. The symptoms of gastroenteritis
appear frequently among diseases associated with different source pathogens.
This is borne out in Table 1.4, which contains a comprehensive grouping and
summary of the characteristics and control of a number of these diseases for easy
reference.
Although comprehensive, the body of information should not be considered
exhaustive or terminally complete, rather the table should serve as an orientation
