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→Factors Involved in the Development of Disease
====Factors Involved in the Development of Disease====
====Factors Involved in the Development of Disease====
There are three factors which conspire with each other to produce disease
1. Animal - its nutritional and immune status, modified by
a. recent or concurrent disease
b. previous exposure to the agent(s) responsible
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2. Agent(s) - a. most do not cause a uniform pattern of disease: host defences are important
b. its capacity to produce disease depends upon
i. the dose and /or
ii. the virulence of the agent
c. several agents may be involved; usually one agent debilitates, allowing others
to exert a greater effect within the body
d. the presence of an agent does not necessarily mean it is the cause of the
disease.
e. the absence of a pathogenic (disease producing) agent from the tissues may
be due to
i. clinical therapy and/or
ii. host defence systems
3. Environment - a. overcrowding of animals
b. mixing animals from differing origins allows 'carriers' (animals which
harbour the pathogenic agent but which do not show signs of disease) to
infect susceptible animals
c. changes in management routine
====Types of Agents Causing Disease====
====Types of Agents Causing Disease====
====Aspects of Disease====
====Aspects of Disease====