Introduction & History of Epidemiology

Epidemiology

Study of disease in population/ herd

Study of factors that cause/encourage diseases

Some diseases are more common in certain geographic areas or at different times of the year

Importance of Livestock

Provides food for human consumption

The major products;

• Milk and meat
• Value Added products
• Draught Animals

Role of livestock in economy

• Livestock-largest contributor to overall agriculture (53.2%)
• Grew by 4.1 % in 2009‐10 as against 3.5 % last year.
• The Fishery sector expanded by 1.4%, against previous year’s growth of 2.3%.

Scope of livestock sector

• Demand for livestock products is increasing
• Population growth rate and increased income are the real reasons
• Increase in red meat prices clearly indicate supply gap
• Tremendous scope of export (rising trend each year)
• Technology gap shows scope for increased production

Health

A state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity"

Disease

A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs.

Infectious diseases

Result from microbes-includes viruses, bacteria, fungi, protozoa, multicellular parasites, and aberrant proteins (Prions).

Non infectious diseases

Also called non communicable diseases- not caused by a pathogen and cannot be shared from one person to another

Including most forms of cancer, heart disease, and genetic disease.

History of Epidemiology

• A milestone in growth of veterinary medicine was the establishment of the first permanent veterinary school at Lyons, France, in 1762.
• Early developments were governed largely by economic rather than humanitarian motives
• Domestic stock was important as a source of food and as working animals
• Economic reasons were more concern about disease in animal populations.

The development of veterinary medicine

• Until the last half of the 20th century, emphasis of veterinary medicine had been on the treatment of individual animals.
• Apart from routine immunization and prophylactic treatment of internal parasites, restricted attention had been given to herd health.
• Comprehensive preventive medicine, which give proper consideration to both infectious and non-infectious diseases was lacking in past.

Domestication of animals

• Dog was probably the first animal to be domesticated when it became the companion of early hunters.
• Sheep & goats-domesticated by 9000 BC in the fertile Nile valley (basis of early pastoral cultures)
• The horse provided the key to successful exploitation of the area north of the Black Sea and a Eurasian horse culture, associated with warrior tribes emerged.
• Religious as well as an economic significance in early civilizations was basis of domestication of animals.
• India is the largest cattle culture.

Changing concepts cause of disease

Approaches to treatment and prevention are the direct result of theories of cause.

Method of treatment used by early Egyptians was incantation (belief in supernatural spirits as a possible cause of disease).

Five main theories (middle of the last century)

Demons (Evil Spirit)

• Early man attributed disease to supernatural powers
• In 'spirit-world', disease could be produced by witches, superhuman entities and spirits of the dead
• Treatment therefore included: placation (stop feeling angry) by sacrifice; exorcism (forcible expulsion); evasion, for instance scattering millet seeds to avoid vampires.

Divine wrath

Argued that disease was the product of a displeased supreme being (Disease was punishment).

Metaphysical medicine

• The moon, stars & planets were considered to affect health
• Treatment frequently included particularly foul medicines and practices that persisted for many centuries.

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).
• 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.

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.

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).

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".

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).

Movement for change

Veterinary medicine has experienced five stable periods and revolutions up to the middle of the 20th century relating to disease control.

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.

The second period: the first century AD until 1762

Veterinarians specialized in equine medicine and surgery, reflecting the importance and value of horses.

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.

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.
• 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.

The fifth period

• The animal-health problems and anomalies stimulated a change in attitude towards disease causality and control.
• 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.

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

Recent trends

• Veterinary services: Control and treat disease individual animal
•  Improving diagnostic procedures
• New opportunities for vaccine production systems
• Multification nature of many diseases 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.

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.

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. 

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.

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
• 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