Lecture 1 Flashcards
What is Health?
Health is a state of complete physical,
mental and social well-being and not
merely the absence of disease or infirmity
What does health in livestock refer to?
!. 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’
- Production: Given proper nutrients and environment
- Reproduction: Given proper nutrients and environment
What is disease?
Disease is the finite abnormality of structure or function with an identifiable pathological basis and recognizable clinical signs
What does Disease include?
- Subclinical (non visible but measureable) and Clinical (overt, visible signs)
- Suboptimal production (below what is expected for that breed
- Welfare (described through 5 freedoms)
What are the 5 freedoms of welfare
- Freedom from hunger and thirst;
- Freedom from discomfort;
- Freedom from pain, injury and disease;
- Freedom to express normal behaviour;
- Freedom from fear and distress.
Classifications of disease
(DAMNIT)
Degenerative
Anomalous
Metabolic
Neoplastic
Infection
Trauma or toxicity
What does degenerative mean?
Structure is altered by age, use or disuse or biochemical changes
Example: arthritis
What does anomalous mean?
Abnormal structure or function: “congenital” (present at birth)
• May be genetic
Example: cleft palate, atresia ani
What does metabolic classification of disease mean?
Due to nutrition, toxins or hormonal activity that alters normal metabolism
What does neoplasm classification of disease mean?
Abnormal growth of cells at the expense of normal tissue structure and function
Examples: Lymphosarcoma, cancer eye
What does infections classification of disease mean?
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
What does Trauma and Toxicity mean in classifications of disease
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)
What is a pathogen (Infectious cause of disease)
• Any disease-producing microorganism or material
• Bacterium, virus, fungus that can cause infection
and/or disease
What is Etiology?
• The study of the causes of disease
• Etiologic agent = causative agent of disease ≠ “the
cause”
What is pathogenesis
• The development of disease, the disease process
• The process by which a pathogen produces disease
What types of infections are responsible for causing disease?
Prions (abnormal forms of PrP proteins causing resistance to proteases), Mycotic (fungal), Parasites (can be intracellular, internal or external)
Contagious VS infectious
What does it mean for something to be contagious?
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
Four ways diseases can be transmitted - HOW?
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)
Disease transmitting - WHO?
Horizontal VS Vertical transmission
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
What is epidemiology?
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
Determinants of Health & Disease
The Epidemiologic Triad
What are the three components?
Host, Agent, Enviornment
Determinants of Disease
1. Host factors – predisposing or protective
• 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
Determinants of Disease
1. Host factors – predisposing or protective
• Immune status
• Herd immunity
• Age
• Genetic
• Physiological state
• Production levels
• Nutritional status
Determinants of disease
- Agent factors
• 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
Determinants of disease
- Environmental Factors
• Temperature
• Humidity
• Stocking density
• Stall design
• Bedding / flooring
• Feeder design
Affects pathogen load
Affects host response
What is “sufficient cause”
• 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
What is Necessary Cause?
• 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
What is carrier state?
• 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
What is Morbidity
Morbidity
• The condition of being diseased
• The amount of disease (frequency)
What is Mortality
Mortality
• The number of deaths (death as a statistic)
What is Case Fatality (rate)
Case Fatality (rate)
• Proportion of animals with a specific
disease that die from it
What is Endemic disease?
• The usual frequency of occurrence of a disease in a population
• Expected
• The constant presence of a disease in a population
What is Epidemic disease?
• An occurrence of an infectious or non-infectious disease to a level in excess of the expected
What is Sporatic disease
• Disease occurs infrequently and not readily predictable
Measures of Disease Occurrence
What does Prevalence of disease measure?
• At a point in time, the number of animals that
are diseased / number of animals in the
population
– E.g. seropre
Measures of Disease Occurrence
What does incidence of disease measure?
• 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
