Lecture 1

Question 1

What is Health?

Answer 1

Health is a state of complete physical,
mental and social well-being and not
merely the absence of disease or infirmity

Question 2

What does health in livestock refer to?

Answer 2

!. Welfare: “the provision of a complete diet,
an environment that is optimal for the animal’s
physiological needs, comfortable to the animal’s senses, in which the animal is secure and free from fear, and with no undue challenge by pathogenic micro-organisms or predators’

2. Production: Given proper nutrients and environment
3. Reproduction: Given proper nutrients and environment

Question 3

What is disease?

Answer 3

Disease is the finite abnormality of structure or function with an identifiable pathological basis and recognizable clinical signs

Question 4

What does Disease include?

Answer 4

1. Subclinical (non visible but measureable) and Clinical (overt, visible signs)
2. Suboptimal production (below what is expected for that breed
3. Welfare (described through 5 freedoms)

Question 5

What are the 5 freedoms of welfare

Answer 5

1. Freedom from hunger and thirst;
2. Freedom from discomfort;
3. Freedom from pain, injury and disease;
4. Freedom to express normal behaviour;
5. Freedom from fear and distress.

Question 6

Classifications of disease

Answer 6

(DAMNIT)

Degenerative
Anomalous
Metabolic
Neoplastic
Infection
Trauma or toxicity

Question 7

What does degenerative mean?

Answer 7

Structure is altered by age, use or disuse or biochemical changes
Example: arthritis

Question 8

What does anomalous mean?

Answer 8

Abnormal structure or function: “congenital” (present at birth)

• May be genetic
Example: cleft palate, atresia ani

Question 9

What does metabolic classification of disease mean?

Answer 9

Due to nutrition, toxins or hormonal activity that alters normal metabolism

Question 10

What does neoplasm classification of disease mean?

Answer 10

Abnormal growth of cells at the expense of normal tissue structure and function

Examples: Lymphosarcoma, cancer eye

Question 11

What does infections classification of disease mean?

Answer 11

Invasion and multiplication of microorganisms in
body tissues, especially causing local cellular injury
due to competitive metabolism, toxins, replication,
antigen-antibody response.

Example: M ycoplasma hyopneumonia causing
pneumonia in pigs

Question 12

What does Trauma and Toxicity mean in classifications of disease

Answer 12

Trauma is a mechanical injury (broken bone/ ruptured muscle)

Toxicity is caused by an exogenous substance that gains access to the system and damages normal
structure, causing dysfunction
(Examples: Lead toxicity)

Question 13

What is a pathogen (Infectious cause of disease)

Answer 13

• Any disease-producing microorganism or material
• Bacterium, virus, fungus that can cause infection
and/or disease

Question 14

What is Etiology?

Answer 14

• The study of the causes of disease
• Etiologic agent = causative agent of disease ≠ “the
cause”

Question 15

What is pathogenesis

Answer 15

• The development of disease, the disease process
• The process by which a pathogen produces disease

Question 16

What types of infections are responsible for causing disease?

Answer 16

Prions (abnormal forms of PrP proteins causing resistance to proteases), Mycotic (fungal), Parasites (can be intracellular, internal or external)

Question 17

Contagious VS infectious

What does it mean for something to be contagious?

Answer 17

Contagious: capable of being transmitted from
animal to animal by contact or close proximity

All contagious diseases are infectious but
not all infectious diseases are contagious

Question 18

Four ways diseases can be transmitted - HOW?

Answer 18

1 Directly: contact between animals

2 Fomites:
• Inanimate objects (shovel, boots)
• Object which is alive but organism doesn’t infect –
passive carrier (e.g. human hands)
• Vehicle – food or water

3.Vectors: Invertebrate animal required for agent life cycle and transmission

4 Infectious secretions or excretions
(Respiratory droplets, saliva, feces, urine)

Question 19

Disease transmitting - WHO?

Horizontal VS Vertical transmission

Answer 19

Horizontal transmission
• Between animals of the
same generation
• Infectious
• Contagious

Vertical transmission
• Between animals of one
generation to a
succeeding generation
• Dam → offspring
• In utero

Question 20

What is epidemiology?

Answer 20

Study of patterns of disease that exist under field conditions, specifically….
• Frequency
• Distribution
• Determinants of health & disease
…in a population

Analogous to pathogenesis in an individual

Question 21

Determinants of Health & Disease
The Epidemiologic Triad

What are the three components?

Answer 21

Host, Agent, Enviornment

Question 22

Determinants of Disease
1. Host factors – predisposing or protective

Answer 22

• Immune status
• Innate – genetic in origin?
• Acquired – colostrum, vaccinated, natural exposure?
• Depends on nature of agent, challenge and environment
• Herd immunity – upcoming lecture
• Age
• Physiologic effect = changes in cell or organ function that happen inevitably with the passage of time
• Associated with changes in production level, immune status, and/or physiologic state
• Genetic
– Simple – Holstein LDA
– Phenotypic – white pigmentation/cancer eye
– Genotype – pigs E coli resistance
• Physiologic state (pregnant/lactating)
• Production level
• Nutritional status

Question 23

Determinants of Disease
1. Host factors – predisposing or protective

Answer 23

• Immune status
• Herd immunity
• Age
• Genetic
• Physiological state
• Production levels
• Nutritional status

Question 24

Determinants of disease

2. Agent factors

Answer 24

• Virulence determenants (Degree of pathogenicity, includes severity, “fitness” of pathogen)

• Pathogen challenge
• The amount of pathogen is important
• Critical load depends on host status
• Environment affects pathogen growth

Question 25

Determinants of disease

3. Environmental Factors

Answer 25

• Temperature
• Humidity
• Stocking density
• Stall design
• Bedding / flooring
• Feeder design

Affects pathogen load
Affects host response

Question 26

What is “sufficient cause”

Answer 26

• Factors working together to produce disease
• Alone, one factor may not be sufficient but in various combinations, disease occurs

• e.g. colostrum intake + colostrum quality + age of piglet + environmental temperature + presence & dose of infecting E. coli

Question 27

What is Necessary Cause?

Answer 27

• Without this factor, disease cannot occur
e.g. E. coli necessary to cause Colibacillosis
• But presence of a disease agent may or may not
be sufficient to cause disease

Question 28

What is carrier state?

Answer 28

• No clinical disease but potential to transmit an
infectious agent
– May remain asymptomatic (never diseased)
– Incubating the disease (eventually or
intermittently affected)
– Convalescing from the disease

Question 29

What is Morbidity

Answer 29

Morbidity
• The condition of being diseased
• The amount of disease (frequency)

Question 30

What is Mortality

Answer 30

Mortality
• The number of deaths (death as a statistic)

Question 31

What is Case Fatality (rate)

Answer 31

Case Fatality (rate)
• Proportion of animals with a specific
disease that die from it

Question 32

What is Endemic disease?

Answer 32

• The usual frequency of occurrence of a disease in a population
• Expected
• The constant presence of a disease in a population

Question 33

What is Epidemic disease?

Answer 33

• An occurrence of an infectious or non-infectious disease to a level in excess of the expected

Question 34

What is Sporatic disease

Answer 34

• Disease occurs infrequently and not readily predictable

Question 35

Measures of Disease Occurrence

What does Prevalence of disease measure?

Answer 35

• At a point in time, the number of animals that
are diseased / number of animals in the
population

– E.g. seropre

Question 36

Measures of Disease Occurrence

What does incidence of disease measure?

Answer 36

• Number of new cases of disease in a specified
time period or risk period / by number at risk
• Implies at least 2 observations or
measurements
• To be included in denominator, must have
been at risk