Abstract
In
this lesson students review some cases and are introduced
to a number of water borne diseases that could have
caused a certain disease. Once students have identified
the disease that has caused the symptoms they must
draw upon their earlier experiences in this learning
cycle to explain what the reaction of the immune system
to the disease might be.
Objectives
Students
will be able:
1.
Compare symptoms of several well-known water-borne
diseases.
2. Use the symptoms and background information on the
disease to explain some of the aspects in terms of immune
response.
Teacher
Background
(This information is also provided to the students in
the Water-borne Diseases
Information Sheet.)
Waterborne diseases are those acquired through the ingestion
of contaminated water. About 80 percent of all diseases
are water-related. In many of these illnesses, water
infiltrated with sewage spread the disease. An infected
person or animal may pass pathogenic bacteria, viruses,
or protozoa through waste into the water supply. Some
bacteria, however, are indigenous to water environments
and are naturally occurring in estuarine bodies of water.
The microorganisms that cause illness cannot be seen,
smelled, or tasted; contaminated water often appears
fresh and clear. This causes particular concern with
municipal water supplies. Contamination may not be detected
until a noticeable number of people have become ill.
One specific bacterium has been isolated from water sediment,
plankton and shellfish (oysters, clams and crabs) located
in the Gulf of Mexico, the Atlantic Coast as far north
as Cape Cod and the entire West Coast. Cases of illness
have also been associated with brackish lakes in New
Mexico and Oklahoma.
Most ailments are caused by the ingestion of water infiltrated
with sewage are intestinal, causing gas, cramping and
diarrhea. Some pathogens (harmful microorganisms) attach
to intestinal linings and produce toxic materials which
the body then tries to purge. Others invade intestinal
epithelial cells and cause inflammation but do not produce
toxins. Still other bacterium occurs naturally and is
not caused by pollution. It does not affect sea life,
but in people, can cause wound infections, gastroenteritis,
(diarrhea and other stomach and intestinal symptoms),
septicemia (blood poisoning) and even death. Fluids containing
disease-fighting white blood cells are secreted into
the intestine to aid in the attacking or flushing of
harmful organisms form the body. Unfortunately, this
loss of fluids from the body also causes dehydration,
the major concern of patients with these types of diseases.
Another concern is to individuals who have a compromised
immune system. In those people, the bacteria can infect
the bloodstream, causing severe life-threatening illness
that can induce fever and chills, decreased blood pressure
and skin sores. When this bacterium causes a bloodstream
infection, it is fatal about 50 percent of the time.
[CDC (Vibrio vulnifcus)]
If a patient is very young, elderly, or malnourished,
dehydration can be life-threatening. Children with diarrhea
must be closely monitored. They have not yet developed
the immunities of adults, and their systems can be quickly
overwhelmed by the shear number of pathogens. As many
as one-third of pediatric deaths in developing countries
can be attributed to diarrhea and resulting dehydration.
Africa, Asia and Latin America experience an estimated
3-5 billion cases of diarrhea, with 5-10 million deaths
each year. Vibrio cholerae, Salmonella sp., and Shigella
species of bacteria are among the leading causes of bacterial
diarrhea. Vibrio vulnificus is a leading cause of reported
death from food-borne illnesses in coastal states such
as Florida. Bacteria are everywhere, including our water.
However, water supplies are monitored to prevent contamination
by fecal pathogens in concentrations that will produce
infections in humans. Water treatment facilities routinely
test for these pathogens by checking the level of indicator
bacteria, such as Escherichia coli (a common organism
in our intestines). If these organisms rise above a set
level, fecal contamination has occurred and more intensive
water testing should begin. This does not mean pathogens
are present, but serves as an “indicator” that
they may be. It may be necessary to accelerate water
treatment procedures. Also, the source of contamination
must be located and protective measures taken to avoid
further contamination.
Until recently, Americans have regularly suffered through
epidemics of waterborne illness such as cholera and typhoid
fever. Improvements in wastewater disposal practices
and the development, protection and treatment of water
supplies have significantly reduced the incidence of
these diseases. The treatment and chlorinating of municipal
water have made infection by microorganisms rare in developed
countries. However, in many developing countries, treatment
of waste water is minimal or nonexistent. In some cases,
sewage and other wastes are dumped directly into rivers
that are used by people downstream for drinking and washing.
Epidemiologists study the incidence, transmission, distribution,
and control of disease. When outbreaks of a particular
disease occur, epidemiologists research symptoms, incidence,
and distribution of cases; they try to determine the
cause of the disease, its means of spreading, and possible
methods for controlling or preventing the illness. With
waterborne diseases, determining how the water supply
was contaminated is critical to solving the problem.
The case histories of affected patients and any association
among patients help epidemiologists solve the mysteries
of the disease.
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