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→Factors Involved in the Development of Disease
* There are three factors which conspire with each other to produce disease.
* There are three factors which conspire with each other to produce disease.
*# The individual animal.
*# '''The individual animal'''.
*#* In particular, the animal's nutritional and immune status
*#* In particular, the animal's nutritional and immune status
*#** This is modified by:
*#** This is modified by:
*#*** Recent or concurrent disease
*#*** Recent or concurrent disease
*#*** Previous exposure to the agent(s) responsible
*#*** Previous exposure to the agent(s) responsible
*# The disease-causing agent(s).
*# '''The disease-causing agent(s)'''.
*#* Most do not cause a uniform pattern of disease
*#* Most do not cause a uniform pattern of disease
*#** Host defences are important in determining the presentation of the disease.
*#** Host defences are important in determining the presentation of the disease.
*#** The dose and /or
*#** The dose and /or
*#** The virulence of the agent
*#** The virulence of the agent
*#* Several agents may be involved.
to exert a greater effect within the body
*#** Usually one agent debilitates, allowing others to exert a greater effect within the body
*#* The presence of an agent does not necessarily mean it is the cause of the disease!
disease.
*#* A pathogenic agent may be absent from the tissues, due to:
*#** Clinical therapy and/or
*#** Host defence systems
*# Environment - a. overcrowding of animals
b. mixing animals from differing origins allows 'carriers' (animals which
b. mixing animals from differing origins allows 'carriers' (animals which
harbour the pathogenic agent but which do not show signs of disease) to
harbour the pathogenic agent but which do not show signs of disease) to