Introduction to preventive vet medicine

VMD – 401 Lectures Theory
Prepared by Dr. Fahad Riaz
Preventive veterinary medicine
Branch of vet medicine that deals with disease o0f infectious origin and of contagious
nature, its occurrence in animal population, its prevention and control by suitable and
appropriate measures
Health
A state of complete harmony or state of complete physical, mental and physiological
well-being
Five freedom of life
For being healthy living one should have freedom from these five fears
1. Fear of hunger
2. Fear of thirst
3. Fear of living
4. Fear of reproduction
5. Fear of social behavior
Disease
A dysfunction or disorder of a part of or complete system of living organism as a result
showing some signs and symptoms local or generalized
Its interaction between two living organism host and the agent if host win the fight it will
resist the disease and if agent is successful then disease set in.
Infectious diseases
Word infection originated from Latin word “Infecere” means to put or dip into. Disease
caused by infectious agents (microbes) e.g. mastitis, Foot and Mouth Disease (FMD)
etc

Contagious diseases
Disease or infection that may be transmitted from an animal to another animal or human
e.g. rabies, tetanus
Infestation
This word is derived from Latin word “infestare” which means disturbed / hostile. It
indicate condition disease due to the presence of parasites e.g. lice, ticks, mites and
other worms. These parasites can act as biological vector and can transmit infection
from diseased one to healthy one
Types of animal diseases on the basis of etiology
Etiology: Study of disease on the basis of causative agent (pathogen).
Pathogen: micro-organism having tendency to cause disease in animal or
humans.
There are two types of disease causing factors
1. Intrinsic Factors
All those factors which are inside the body of living organism causing disease like
metabolic disturbance e.g. Ketosis, milk fever etc
2. Extrinsic factors
All those factors which are outside the body of living organism causing disease these
are generally categorized as
a. Mechanical: Include all those extrinsic factors that can cause Injury , trauma
or wound.
b. Physical: Include all those extrinsic factors that are due to influence of
environment e.g. Hot, Cold, Dust or smoke
c. Chemical agents: e.g. acid, alkali or poison

d. Infectious agents: e.g. virus, bacteria, protozoa or fungi etc
Sterilization
It’s the process of destruction of all forms of micro-organisms by using the
heat. The word sterile / sterilize indicate total absence or killing of microbes
Moist heat
a. Autoclave
b. Boiling
c. Pasteurization
Dry heat
a. Red hot
b. Flaming
c. Hot air oven
Disinfection
Use of antimicrobial agents that are applied to the surface of non-living objects to
destroy microorganisms that are living on the objects.
Quality of a good Disinfectant
a. Economic for consumer
b. No offensive odour
c. No harmful effect on consumer and animals e.g. action should not
be so strong in case if animal lick the agent
d. Must act when diluted
e. Must make homogeneous mixture when diluted in water
Importance of diseases on national economy
Agriculture provides 18.5% of total GDP of the country and 38.5%
employment to countries labor force. Livestock sector contributes 60.5%
share in agriculture or 11.2% in countries GDP. Cross value addition of

livestock increased from 1384 billion (2017-18) to 1440 billion (2018-19).
Gross production of milk 59759 thousand tones, meat 4474 thousand
tones and 19052 million numbers.
Any type of disease results in disturbance of these numbers like if a
buffalo gets infected with mastitis it is reported that 437 litters is lost per
lactation in the animals
Losses occur due to disease include
a. Expanses of treatment
b. Production loss
c. Discarding animals or animal product
Defenses against diseases
Natural barriers and the immune system defend the body against organisms that can
cause infection.
Natural barriers include the skin, mucous membranes, tears, earwax, mucus, and
stomach acid. Also, the normal flow of urine washes out microorganisms that enter the
urinary tract.
The immune system uses white blood cells and antibodies to identify and eliminate
organisms that get through the body’s natural barriers.
Natural Barriers
Usually, the skin prevents invasion by microorganisms unless it is damaged (for
example, by an injury, insect bite, or burn).
Mucous membranes, such as the lining of the mouth, nose, and eyelids, are also
effective barriers. Typically, mucous membranes are coated with secretions that fight
microorganisms. For example, the mucous membranes of the eyes are bathed in
tears, which contain an enzyme called lysozyme that attacks bacteria and helps
protect the eyes from infection.

The airways filter out particles that are present in the air that is inhaled. The walls of
the passages in the nose and airways are coated with mucus. Microorganisms in the
air become stuck to the mucus, which is coughed up or blown out of the nose. Mucus
removal is aided by the coordinated beating of tiny hairlike projections (cilia) that line
the airways. The cilia sweep the mucus up the airways, away from the lungs.
The digestive tract has a series of effective barriers, including stomach
acid, pancreatic enzymes, bile, and intestinal secretions. These substances can kill
bacteria or prevent them from multiplying. The contractions of the intestine (peristalsis,
which moves contents of the bowel through the digestive tract), and the normal
shedding of cells lining the intestine help remove harmful microorganisms.
The urinary tract also has several effective barriers. The bladder is protected by
the urethra, the tube that drains urine from the body. In males, the urethra is long
enough that bacteria are seldom able to pass through it to reach the bladder, unless
the bacteria are unintentionally placed there by catheters or surgical instruments. In
females, the urethra is shorter, occasionally allowing external bacteria to pass into the
bladder. In both sexes, when the bladder empties, it flushes out any bacteria that
reach it.
The Blood
The body also defends against infection by increasing the number of certain types of
white blood cells (neutrophils and monocytes), which engulf and destroy invading
microorganisms. The increase can occur within several hours, largely because white
blood cells are released from the bone marrow, where they are made. The number of
neutrophils increases first. If an infection persists, the number of monocytes increases.
The blood carries white blood cells to sites of infection.
The number of eosinophils, another type of white blood cell, increases in allergic
reactions and many parasitic infections, but usually not in bacterial infections.

However, certain infections, such as typhoid fever, viral infections, and bacterial
infections that overwhelm the immune system, can lead to a decrease in the white
blood cell count.
Inflammation
Any injury, including an invasion by microorganisms, causes inflammation in the
affected area. Inflammation, a complex reaction, results from many different
conditions. The damaged tissue releases substances that cause inflammation and that
direct the immune system to do the following:
• Wall off the area
• Attack and kill any invaders
• Dispose of dead and damaged tissue
• Begin the process of repair
However, inflammation may not be able to overcome large numbers of
microorganisms.
During inflammation, the blood supply increases, helping carry immune cells to the
affected area. An infected area near the surface of the body becomes red and warm.
The walls of blood vessels become more porous, allowing fluid and white blood cells
to pass into the affected tissue. The increase in fluid causes the inflamed tissue to
swell. The white blood cells attack the invading microorganisms and release
substances that continue the process of inflammation.
Other substances trigger clotting in the tiny vessels (capillaries) in the inflamed area,
which delays the spread of the infecting microorganisms and their toxins.

Many of the substances produced during inflammation stimulate the nerves, causing
pain. Reactions to the substances released during inflammation include the chills,
fever, and muscle aches that commonly accompany infection.
Immune Response
When an infection develops, the immune system also responds by producing several
substances and agents that are designed to attack the specific invading
microorganisms. Examples are
• Killer T cells (a type of white blood cell) that can recognize and kill the invading
microorganism
• Antibodies that target the specific invading microorganism
Antibodies attach to and immobilize microorganisms. They kill them outright or help
neutrophils target and kill them.
How well the immune system defends the body against each microorganism depends
partly on a person's genetic make-up.
Fever
Body temperature increases as a protective response to infection and injury. An
elevated body temperature (fever) enhances the body’s defense mechanisms,
although it can cause discomfort.
A part of the brain called the hypothalamus controls body temperature. Fever results
from an actual resetting of the hypothalamus's thermostat. The body raises its
temperature to a higher level by moving (shunting) blood from the skin surface to the
interior of the body, thus reducing heat loss. Shivering (chills) may occur to increase
heat production through muscle contraction. The body's efforts to conserve and
produce heat continue until blood reaches the hypothalamus at the new, higher
temperature. The new, higher temperature is then maintained. Later, when the
thermostat is reset to its normal level, the body eliminates excess heat through
sweating and shunting of blood to the skin.

Certain people (such as alcoholics, the very old, and the very young) are less able to
generate a fever. These people may experience a drop in temperature in response to
severe infection.
Principals of treatment of disease
It clears the concept of or planning of treatment e.g. one would be to reduce the
effects of disease and the other to kill the cause of the disease
i) To reduce the effects of the disease
a. This can be done by taking medicines to bring down the effects of the
disease like fever, pain or loose motions etc. and by taking bed rest to
conserve our energy.
ii) To kill the microbes :-
a. This can be done by taking suitable antibiotics and drugs which kills
the microbes and the disease is cured Principles of prevention
The goals of medicine are to promote health, to preserve health, to restore health when
it is impaired, and to minimize suffering and distress.
Prevention, Levels of prevention, disease control and eradication
Prevention; Definition and Concept
Actions aimed at eradicating, eliminating or minimizing the impact of disease and
disability, or if none of these are feasible, retarding the progress of the disease and
disability.
The concept of prevention is best defined in the context of levels, traditionally called
primary, secondary and tertiary prevention. A fourth level, called primordial prevention,
was later added.
Determinants of Prevention
Successful prevention depends upon:
1) a knowledge of causation,
2) dynamics of transmission,

3) identification of risk factors and risk groups,
4) availability of prophylactic or early detection and treatment measures,
5) an organization for applying these measures to appropriate persons or groups,
6) and continuous evaluation of and development of procedures applied
Leavell’s Levels of Prevention
Primordial prevention
Primordial prevention consists of actions and measures that inhibit the
emergence of risk factors in the form of environmental, economic, social, and behavioral
conditions and cultural patterns of living etc.
Primary prevention
Primary prevention can be defined as the action taken prior to the onset of
disease, which removes the possibility that the disease will ever occur.
It signifies intervention in the pre-pathogenesis phase of a disease or health problem.
Primary prevention may be accomplished by measures of “Health promotion” and
“specific protection”. It includes the concept of "positive health", a concept that
encourages achievement and maintenance of "an acceptable level of health that will
enable every individual to lead a socially and economically productive life".
Primary prevention may be accomplished by measures designed to promote general
health and well-being, and quality of life or by specific protective measures.

Secondary prevention
It is defined as “ action which halts the progress of a disease at its incipient stage
and prevents complications.” The specific interventions are: early diagnosis (e.g.
screening tests, and case finding programs….) and adequate treatment.
Secondary prevention attempts to arrest the disease process, restore health by seeking
out unrecognized disease and treating it before irreversible pathological changes take
place, and reverse communicability of infectious diseases.
It thus protects others from in the community from acquiring the infection and thus
provides at once secondary prevention for the infected ones and primary prevention for
their potential contacts.
Tertiary prevention
It is used when the disease process has advanced beyond its early stages.
It is defined as “all the measures available to reduce or limit impairments and
disabilities, and to promote the patients’ adjustment to irremediable conditions.”
Intervention that should be accomplished in the stage of tertiary prevention are disability
limitation, and rehabilitation.
Control of DIsease
The term disease control describes ongoing operations aimed at reducing:
I. The incidence of disease
II. The duration of disease and consequently the risk of transmission
III. The effects of infection, including both the physical and psychosocial
complications
IV. The financial burden to the community.
Control activities focus on primary prevention or secondary prevention, but most
programs combine both.
Disease Elimination
Between control and eradication, an intermediate goal has been described,
called "regional elimination". The term "elimination" is used to describe interruption of
transmission of disease, as for example, elimination of measles, polio and diphtheria
from large geographic regions or areas. Regional elimination is now seen as an
important precursor of eradication
Disease Eradication
Eradication literally means to "tear out by roots". It is the process of “Termination
of all transmission of infection by extermination of the infectious agent through
surveillance and containment”. Eradication is an absolute process, an "all or none"
phenomenon, restricted to termination of an infection from the whole world. It implies
that disease will no longer occur in a population. To-date, only one disease has been
eradicated, that is smallpox.

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