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| ====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 |
| + | 10 |
| + | 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==== |