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CHAPTER ONE
BACKGROUND
Since times immemorial, all things have been known to interact. This interaction ranges
from plants- mineral nutrients relationship to Algae- Fungus relationship (Lichens) and
even human- micro organisms relationship. The result of these interaction are diverse in
nature, it can be beneficial as in the bacteria in the digestive tract of cattle, while the
adverse results ends up in diseases1. Diseases can either be communicable or
incommunicable.
Communicable diseases are diseases that can be transmitted from one person to
another. This may occur by the direct physical contact by common handling of an
object that has picked up infective microorganisms through a disease, or by spread of
infected droplets coughed or exhaled into the air. Table 1 shows some communicable
diseases, their causative agents and mode of transmission.
Micro organisms e.g. bacteria, fungus viruses etc are small organisms invisible to the
naked eyes but visible by the aid of a microscope that cause various diseases to man
and animals alike. Vectors, on the other hand are organisms that carry about these
disease- causing micro organisms.
Transmission of diseases is by diverse mode. This can be as in the case of AIDSsexual intercourse, blood transfusion; or by insect bite, infected food and water and so
on.
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A disease is a disorder with a specific cause and recognizable signs and symptoms; any bodily
abnormality or failure to function properly, except that resulting directly from physical injury the latter,
however may open the way for disease.
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Table 1
Some Diseases, their Mode of Transmission and Causative Organisms
Disease
AIDS
Chancroid
Chicken Pox
Cholera
Cryptosporidiosis
Diphtheria
German Measles
Transmission Mode
Sexual Intercourse, Blood Transmission
Sex
Air Borne
Water Borne
-----Air- Borne
Air Borne
Micro organism
Virus
Bacterium
Virus
Bacteria
Protozoa
Bacteria
Virus
Giardiasis
Gonorrhea
Contact, Sex
Sex
Protozoa
Bacterium
Hepatitis
Influenza
Leishmaniasis
Leprosy
Malaria
Measles
Mumps
Pneumonia,
Poliomyelitis
Rabies
Shigellosis
Sleeping Sickness
Smallpox
Strep Throat
Syphilis
Water, Blood, Feaces
Air Borne
Sand fly Bite
------Mosquito
Air Borne and Body Ants
Air
Air
Water, Food
Animal Bite (Infected Dogs)
Water
Tse-Tse
Air
------Sex
Virus
Virus
Protozoa
Bacteria
Protozoa
Virus
Virus
Bacteria
Virus
Virus
Bacterium
Protozoa
Virus
Bacteria
Bacterium
Tetanus
Toxoplasmosis
Tuberculosis
Typhoid Fever
Whooping Cough
Yellow Fever
Water And Air
Raw meat
Air
Water- Borne
Air
Aedes Mosquito Bite
Bacteria
Protozoa
Bacteria
Bacteria
Bacterium
Virus
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CHAPTER TWO
SOME COMMUNICABLE DISEASES
2.1
Influenza- a viral disease
Influenza, also known as flu, is a contagious infection primarily of the respiratory tract.
Influenza is sometimes referred to as grippe. Influenza is caused by a virus transmitted
from one person to another in droplets coughed or sneezed into the air. It is
characterized by cold-like symptoms plus chills, fever, headaches, muscle aches, and
fatigue. Most people recover completely in about a week. But some people are
vulnerable to complications such as bronchitis and pneumonia. This group includes
children with asthma, people with heart or lung disease, and the elderly.
In addition to humans, influenza occurs in pigs, horses, and several other mammals as
well as in certain wild and domesticated birds. At least some influenza viruses can
jump from one species to another. Also Avian Flu that occurred briefly recently.
Because influenza is highly contagious and spreads easily, it usually appears as
epidemics—that is, outbreaks involving many people. If an outbreak spreads around the
world—not uncommon in this age of rapid international travel—it is called a pandemic.
2.1.1
Cause
Today, scientists know that members of the family Orthomyxoviridae, a group of
viruses that infect vertebrate animals, cause influenza. The virus consists of an inner
core of the genetic material ribonucleic acid (RNA) surrounded by a protein coat and an
outer lipid (fatty) envelope. From this envelope, spikes of proteins called hemagglutinin
and neuraminidase stick out.
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Once a person has been infected by a specific strain of influenza, he or she has built up
immunity to that strain in the form of antibodies. The person’s immune system then can
recognize the strain’s hemagglutinin or neuraminidase and attack them if they reappear.
The
antibodies
offer
some
protection
against
antigenic
drifts,
Scientists do not understand exactly what causes antigenic shifts. One leading theory
suggests that a human strain and an animal strain recombine to create a new strain. This
strain has the ability to infect humans but has antigens on its surface that are unfamiliar
to the human immune system.
2.2.1
Transmission
Influenza viruses pass from person to person mainly in droplets expelled during
sneezes and coughs. When a person breathes in virus-laden droplets, the hemagglutinin
on the surface of the virus binds to enzymes in the mucous membranes that line the
respiratory tract. The enzymes, known as proteases, cut the hemagglutinin in two,
which enables the virus to gain entry into cells and begin to multiply. These proteases
are common in the respiratory and digestive tracts but not elsewhere, which is why the
flu causes primarily a respiratory illness with occasional gastrointestinal symptoms.
Although an influenza epidemic can occur at any time of year, flu season in temperate
regions typically begins with the approach of winter—November in the Northern
Hemisphere, April in the Southern Hemisphere. Flu viruses spread more easily during
cold weather.
2.1.3
Prevention and Treatment
There is no specific cure for influenza. Recommended treatment usually consists of bed
rest and increased intake of nonalcoholic fluids until fever and other symptoms lessen
in severity. Certain drugs have been found effective in lessening flu symptoms, but
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medical efforts against the disease focus chiefly on prevention by means of vaccines
that create immunity.(Microsoft Encarta, 2009)
2.2
Tuberculosis- bacterial disease
Tuberculosis (TB) is a chronic or acute bacterial infection that primarily attacks the
lungs, but which may also affect the kidneys, bones, lymph nodes, and brain. The
disease is caused by Mycobacterium tuberculosis, a rod-shaped bacterium. Many
people harbor the bacteria but have no symptoms of disease. When symptoms develop,
they include coughing, chest pain, shortness of breath, loss of appetite, weight loss,
fever, chills, and fatigue.
2.2.1
Transmission
The TB-causing bacteria are transmitted from person to person, usually in infected air
droplets. When someone who has symptomatic TB coughs, sneezes, or speaks, small
particles that carry two to three bacteria surrounded by a layer of moisture are released
in the air. When someone else inhales these particles, the bacteria may lodge in that
person’s
lungs.
A less common route of
transmission
is
through
the
skin.
A person may become infected with TB bacteria and not develop the disease. The
immune system may destroy the bacteria completely. Someone with an inactive
infection cannot transmit the disease.
2.2.2
Treatment and Prevention
General preventive measures can be taken to reduce the spread of TB in public places.
Ventilation systems lessen the chance of infection by dispersing the bacteria.
Ultraviolet lighting also reduces, but does not eliminate, the threat of infection by
killing TB bacteria in confined spaces. Vaccines, such as the bacillus Calmette-Guerin
(BCG) vaccine, prepared from bacteria that have been weakened, are another
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preventive measure. The BCG vaccine is most effective in preventing childhood cases
of TB.(Microsoft Encarta, 2009)
2.3
Toxoplasmosis- protozoan disease
Toxoplasmosis, is a common parasitic infection in humans, warm-blooded animals, and
birds, transmitted by contact with the microorganism Toxoplasma gondii. The disease
normally runs a mild course, with a few noticeable symptoms resembling those of the
common cold. If contracted by a woman during pregnancy, however, toxoplasmosis
can cause serious birth defects. In people whose immune system has been suppressed
by age or other diseases, such as acquired immunodeficiency syndrome (AIDS),
toxoplasmosis can cause severe nervous system disease.
2.3.1
Transmission
The toxoplasmosis parasite is commonly present in cattle, poultry, and many domestic
animals without any harmful effects; however, it continues to live in raw meat after
slaughter until the meat is cooked, dried, or frozen for a prolonged period. The two
major causes of human toxoplasmosis infection are the consumption of raw or
undercooked meat and contact with the feces of the domestic cat.
2.3.2
Prevention
A single infection normally ensures immunity. Serious infection by toxoplasmosis can
be effectively prevented by the avoidance of raw meat and by ensuring that all rarecooked meats are heated throughout to at least 60° C (140° F). Contact with infected or
unfamiliar cats and cat feces should be avoided, and the cat litter box should be emptied
every day because the parasite eggs in cat feces do not become infective until two to
four days after excretion.(Microsoft Encarta, 2009)
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CHAPTER THREE
CONCLUSION
Diseases have diverse causes, which can be classified into two broad groups: infectious
and noninfectious. Infectious diseases can spread from one person to another and are
caused by microscopic organisms that invade the body. Noninfectious diseases are not
communicated from person to person and do not have, or are not known to involve,
infectious agents.
Since the mode of transmission of most of these diseases are known, and as popularly said that
prevention is better than cure, it is the role of the Environmental Engineer to

Manage water treatment plants, so as to make potable water available

Manage the Solid wastes in the environment

Treat wastewater, design good sewage systems and control all sorts of pollution.
When all these are properly done, the transmission of diseases will be greatly reduced because
of the hygienic and healthy environment that will ensue.
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References
Microsoft Encarta, 2009. Microsoft Corporation. Racamond USA.