Vety_Epidemiology_Notes_(Part-1)[1]

Page 1: Definitions, Components and Aims of Epidemiology

Introduction

• Epidemiology: An ancient science gaining significance after Louis Pasteur's germ theory in the 1800s.
• Definition: The study of disease occurrence in different groups and the reasons behind it. It answers the questions: WHO, WHEN, WHERE?
• Epidemiology vs. Epizootiology: Epidemiology studies human populations, while epizootiology focuses on animal populations (e.g., diseases exclusive to dogs, like parvovirus).
• Epidemic, Epizootic, and Epornitic: Outbreaks termed as epidemics (humans), epizootics (animals), and epornitics (avian).
• Key Figures: John Snow (father of modern epidemiology) and Calvin W. Schwabe (father of veterinary epidemiology).

Epidemiology Definition

• Origin of "Epidemiology": From Greek
  • Epi: Upon/among
  • Demos: People/population
  • Logos: Study/discourse
  • Literal meaning: Study of what is upon the people.
• Thrusfield's definition: Key focus on disease and factors determining occurrence in populations.
• CDC Definition: Scientific study of distribution and determinants of health-related states/events in specified populations, crucial for public health.
• Veterinary Epidemiology: Focuses on investigation and control of animal diseases and health events.

Page 2: Veterinary Epidemiology

Key Focus Areas

• Study infectious and non-infectious diseases in animals.
• Zoonotic disease surveillance and control (e.g., rabies).
• Disease prevention strategies in livestock and wildlife.
• Public health and food safety.

Approaches to Study Disease

1. Clinical Approach: Examining individual animals to correlate clinical signs for treatment planning.
2. Microbial/Pathological Approach: Investigates organisms causing diseases, their lifecycle, transmission, pathogenesis, and environmental survival.
3. Epidemiological Approach: Studies disease distribution in populations, focusing on frequency, ecology, and holistic views of disease occurrence.

Page 3: Relationship Between Fields

Comparing Fields

Page 4: Aims and Objectives of Epidemiology

Aims

1. Minimize or eradicate diseases and health problems.
2. Reduce future disease occurrence.
3. Define the magnitude of disease conditions.
4. Identify etiological factors.
5. Provide data for disease control program planning and evaluation.

Objectives

1. Determine origins of known diseases.
2. Investigate and control unknown disease causes.
3. Acquire ecology and natural history information of diseases.
4. Plan and assess disease control programs.
5. Assess economic effects of diseases and analyze alternative control strategies.

Uses of Epidemiology

1. Investigating disease outbreaks: Identifying sources, transmission modes, and risk factors.
2. Investigating diseases of unknown etiology: Understanding causes and patterns.
3. Disease surveillance: Continuous data monitoring to detect outbreaks.
4. Disease control programs: Planning, monitoring, and evaluating intervention activities.

Page 5: Herd Health and Research

Herd/Flok Health and Production

• Implements strategies for livestock health, productivity, and welfare.
• Focus on disease prevention, monitoring, vaccination, biosecurity, and veterinary assessments.

Research

• Field data collection coupled with laboratory support enhances outbreak understanding.
• Development of tests, causal associations, and therapeutic methods are integral to epidemiological research.

Page 6: Important Terms in Epidemiology

• Population: Group of individuals sharing characteristics studied in research.
• Study Population: Specific group selected for analysis.
• Disease Frequency: Measure of disease occurrence in a population, using incidence/prevalence rates.
• Determinants: Factors influencing disease occurrence and distribution.
• Distribution: Pattern of disease occurrence analyzed by time, place, and person.
• Case: Individual identified with a specific disease.
• Variable: Measurable characteristics affecting study outcomes.
• Risk Factors: Characteristics increasing disease likelihood.
• Occurrence: Manifestation of disease in a population.
• Incidence: New disease cases in a defined period.
• Prevalence: Total cases in a population at a specific time.
• Incubation Period: Time from infection to sympton appearance.

Page 7: Epidemiology Subdisciplines

• Clinical Epidemiology: Improving clinical practices using epidemiological principles.
• Genetic Epidemiology: Studying genetic factors' roles in disease distribution.
• Computational Epidemiology: Utilizing computer science for epidemiological modeling.
• Field Epidemiology: Practicing epidemiology in urgent response situations.
• Social Epidemiology: Examining social factors impacting health disparities.
• Environmental Epidemiology: Investigating environmental influences on health.
• Infectious Disease Epidemiology: Focusing on infectious disease determinants.
• Chronic Disease Epidemiology: Studying prevention and distribution of chronic diseases.
• Nutritional Epidemiology: Nutrition's role in disease prevention and health promotion.
• Molecular Epidemiology: Utilizing molecular biology to study disease etiology.

Page 8: Components of Epidemiology

Disease Frequency

• Measurement of health-related events using rates/ratios.
• Crucial for comparing disease occurrence across populations.

Disease Distribution (Time, Place, Person)

• Identifying patterns of disease distribution.
• Developing hypotheses and guiding public health interventions.

Determinants of Disease (Host, Agent, Environment)

• Factors influencing disease causation:
  • Host Factors: Genetic makeup, immunity, age.
  • Agent Factors: Pathogens, toxins, disease-causing entities.
  • Environmental Factors: Climate, living conditions.

Page 9: Theories of Disease Causation

Koch’s Postulates (1884)

1. Microorganism identification linked to the disease.
2. Microorganism isolation and culture.
3. Disease induction in a healthy individual by the cultured organism.
4. Re-isolation of the microorganism from the experimental host. Limitations: Fails to explain multifactorial causation and non-infectious diseases.

Evans’ Principles (1976)

• Modern adaptation incorporating epidemiological and immunological evidence.

1. Higher disease prevalence in the exposed vs. non-exposed.
2. Commonality of exposure in diseased subjects.
3. Higher disease incidence in exposed.
4. Temporal association between exposure and disease.
5. Spectrum of responses to exposure.

Hill’s Criteria of Causation (1965)

• Nine criteria necessary to establish causal relationships between risk factors and disease.

1. Strength of association.
2. Temporality of exposure.
3. Consistency across studies.
4. Theoretical plausibility.
5. Coherence of findings.
6. Specificity of association.
7. Biological gradient (dose-response).
8. Experimental evidence.
9. Analogy with known associations.

Page 10: Factors Influencing Disease in Livestock

The Cause of Disease

• Diseases have underlying causes, often related to agents that modify health and productivity.
• Health definition by WHO: A state of complete well-being.

Factors Categorized by Disease Distribution and Causation

• Descriptive Epidemiology: Individual, place, and time factors.
• Epidemiological Triad: Host, agent, and environmental factors.

Individual, Place, and Time Factors

Individual Factors

• Characteristics such as age, breed, and immunity.

Spatial Factors

• Influences like geography, climate, and management practices.

Temporal Factors

• Changes in disease frequency over time, illustrated by epidemic curves.

Host, Agent, and Environment

• Interactions between host, agent, and environment determine disease transmission.

Page 11: Determinants of Disease

Definition

• Determinants: Factors affecting disease frequency or characteristics.
• Example: Diet as a determinant in bovine hypomagnesaemia.

Classification of Determinants

1. Primary: Major factors inducing disease (e.g., exposure to pathogens).
2. Secondary: Predisposing or enabling factors related to disease susceptibility.

Intrinsic and Extrinsic Determinants

• Intrinsic: Individual characteristics (genetic, physiological).
• Extrinsic: Environmental influences (climate, management).

Page 12: Interaction of Determinants

• Determinants do not act in isolation; interactions can induce disease.

Page 13: Variables in Epidemiology

Definitions

• Variable: Measurable characteristics in investigation (e.g., weight, age).
• Study Variable: Variable under consideration in an investigation.

Types of Variables

1. Qualitative Variables: Categorical variables without numerical measurement (e.g., breed, age).
   • Nominal: No natural order (e.g., coat color).
   • Ordinal: Ordered categories (e.g., body condition scores).
2. Quantitative Variables: Measurable numerical variables (e.g., body temperature).
   • Discrete: Whole numbers (e.g., puppies in a litter).
   • Continuous: Values within a range (e.g., weight of a dog).

Page 14: Hypothesis in Epidemiology

• Hypothesis: Proposed explanations for phenomena involving relationships between variables.

Importance of Hypothesis

• Must be testable against reality to confirm/disprove outcomes.

Types of Hypothesis

• Null Hypothesis: Assumes no relationship (e.g., feed has no effect).
• Alternate Hypothesis: Assumes relationship exists (e.g., feed significantly affects performance).
• Causal Hypothesis: Suggests direct effects between variables.

Page 15: Epidemiological Studies

Approaches in Epidemiology

1. Descriptive Epidemiology: Observational and recording methodologies to generate hypotheses.
2. Analytical Epidemiology: Analytical techniques applied to observations for causal inference.
3. Experimental Epidemiology: Controlled experiments to study causation through exposure manipulation.
4. Theoretical Epidemiology: Use of mathematical models to represent disease occurrence patterns.

Qualitative vs. Quantitative Studies

Page 16: Conclusion

• Epidemiology encompasses a range of studies aimed at understanding disease dynamics.
• A comprehensive understanding of determinants, interactions, and variable influences is crucial for effective public health strategy development.