History of epidemiology (2)


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History of epidemiology (2)

  1. 1. Prof. Dr. Mansur-ud-Din Ahmad Part-II
  2. 2. The universe of natural law Greeks thought-disease was the result of derangement of four humours of the body Four humours were associated with four properties (heat,moisture, dryness and cold) and with four elements (air, earth, water and fire)
  3. 3. The universe of natural law  Diseases were considered to be caused by external forces, including climatic and geological changes  The word 'malaria' literally means 'bad air' and hints at the 19th century belief that the disease was caused by stale air.  The Greek idea of disease was susceptible to scientific investigation
  4. 4. Contagion  Idea-diseases can be transmitted from one animal to another has its ubiquitous origins  The Romans believed that disease could be spread by airborne seeds  The primitive Hindus associated sick rats with human plague, the first suggestion of a zoonosis.
  5. 5. Germ Theory of Diseases  Main advances-identification of microbes as causes of infectious diseases (19th century)  Louis Pasteur's investigation of anthrax & rabies  Robert Koch's discovery of bacteria causing TB & cholera firmly established microbiology (downfall-miasmatic theory)
  6. 6. Miasmatic Theory Of Disease Miasmatic theory of disease- such as cholera were caused by a miasma (ancient Greek:"pollution"), a noxious form of "bad air"
  7. 7. Microbes as cause of infection  The set of postulates formulated by Koch to define causal agents-used to identify many microbial diseases since those early days of bacteriology  Viruses discovered in late 19th century (1892) Iwanowsky demonstrated that tobacco mosaic disease could be transmitted by sap (filterable agent)
  8. 8. Movement for change Veterinary medicine has experienced five stable periods and revolutions up to the middle of the 20th century relating to disease control
  9. 9. The first period: until the first century AD  Initial domestication of animals brought man into close contact with animals and therefore with their diseases  Humoral pathology developed and the miasmatic theory of cause evolved.  Slaughter became preventive strategies
  10. 10. The second period: the first century AD until 1762 Veterinarians specialized in equine medicine and surgery, reflecting the importance and value of horses
  11. 11. The third period: 1762-1884  The animal plagues, especially those of cattle, became particularly common in Europe with the introduction of rinderpest from Asia  Public concern, highlighted by the rinderpest outbreak of 1865 was responsible for the establishment of the British State Veterinary Service  By the mid-19th century, disinfection was also being applied to control the disease
  12. 12. The fourth period: 1884-1960  Treatment of disease was based on laboratory diagnosis involving isolation of agents and identification of lesions followed by Therapy  The discovery of disease vectors facilitated prevention by vector control
  13. 13. The fourth period: 1884-1960 Many infectious diseases were either effectively controlled /eradicated using new techniques of the microbial revolution and older techniques including quarantine, importation restrictions, slaughter and hygiene
  14. 14. The fifth period  The animal-health problems and anomalies stimulated a change in attitude towards disease causality and control
  15. 15. The fifth period  Veterinary services Veterinarians practicing in the livestock sector continue to control and treat disease in individual animals.  Developments in molecular biology are improving diagnostic procedures
  16. 16. New control strategies Two major strategies: the structured recording of information on disease Analysis of dis. in populations Surveillance & monitoring: intensive investigation of particular diseases
  17. 17. Recent trends  Veterinary services : Control and treat disease individual animal  Improving diagnostic procedures  New opportunities for vaccine production systems  Multification nature of many disease necessitates modification of the environment of the animal and management practices.  Food animals-reduced levels of production  Diseases assessed in terms of suboptimal health, manifested by decreased herd performance  Select suitable ‘performance indicators’ (e.g., ‘calving to conception interval’) herd that miss the targets.  Performance-related diagnosis.  Veterinarian, involved in husbandry, management and nutrition. Veterinarian’s evolving role in animal production.  Investigations of specific animal health problems of complex cause, such as mastitis.
  18. 18. Food Quality  Area of concern (Vet. public health) is food quality  Guaranteeing wholesomeness of food at the abattoir, and addresses all levels of the production chain.  Establishment of quality assurance programs on the farm, using techniques such as HACCP (Hazard Analysis Critical Control Points), in focus from quality control of food throughout the production.  Quantitative evaluation of the risk of transmission of infection throughout the chain
  19. 19. Animal welfare  Obvious aspects of animal welfare are deliberate physical abuse (non-accidental injury) and neglect; surgical mutilation (tail docking of dogs)  Welfare in livestock production systems is often evaluated in the context of the ‘five freedoms’  freedom from hunger and thirst;  freedom from discomfort;  freedom from pain, injury and disease;  freedom from fear and distress.
  20. 20. National & international disease reporting  Improved disease reporting systems at the national & international level in the prevention of spread of infectious agents form one country to another.  Residues need to be identified and eliminated-pesticides and hormones, antibiotic residues  Free internal market in the European Union, and global goals to liberalize international trade through the World Trade Organization (WTO)  highlighting the requirement for comprehensive disease reporting  Established organizations, such as the Office International des Epizooties (OIE), are modifying their goals and reporting techniques, taking account of these new requirements.
  21. 21. What Is a "Herd Health"  Herd health plans are designed by herd veterinarian and producer to reduce disease incidence, provide effective diagnosis and treatment protocols, and improve productivity  Herd health Includes:  Routine visits by veterinarian at specific times of year  Training of employees  Health and production records  Economic analysis of decisions
  22. 22. Herd health  Herd health is a key driver of profitability in today’s production environment.  Maintaining health is extremely challenging, particularly as management systems become more intensive and profit margins are squeezed.  Disease robs profits and productivity by reducing growth, increasing deads, lightweights and culls, and adding drug and vaccine costs.  A healthy and robust immune system protects profits and animal welfare by minimizing the incidence and effects of disease