Changes

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''' - in particular, the animal's nutritional and immune status, which may be modified by recent or concurrent disease, and/or previous exposure to the agent(s) responsible.

#'''The individual animal''' - in particular, the animal's nutritional and immune status, which may be modified by recent or concurrent disease, and/or 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. The host defences are important in determining the presentation of the disease. An agent's capacity to produce disease depends upon the dose and the virulence of the agent.  

Most do not cause a uniform pattern of disease. The host defences are important in determining the presentation of the disease.

 

An agent's capacity to produce disease depends upon the dose and the virulence of the agent.  

Bear in mind that several agents may be involved - often one agent debilitates, allowing others to exert a greater effect that normal within the body. The presence of an agent does not necessarily mean it is the cause of the disease! On occasions, a pathogenic agent may be absent from the tissues, due to either clinical therapy or the action of the host defence systems

Bear in mind that several agents may be involved - often one agent debilitates, allowing others to exert a greater effect that normal within the body. The presence of an agent does not necessarily mean it is the cause of the disease! On occasions, a pathogenic agent may be absent from the tissues, due to either clinical therapy or the action of the host defence systems

 

#'''Environment''', for example: in the overcrowding of animals, mixing animals from differing origins and interaction with carriers are allowed to infect susceptible animals. Carriers are animals which harbour the pathogenic agent but do not show signs of disease. Changes in management routine may also affect susceptibility to disease.

3. '''Environment''', for example: in the overcrowding of animals, mixing animals from differing origins and interaction with carriers are allowed to infect susceptible animals. Carriers are animals which harbour the pathogenic agent but do not show signs of disease. Changes in management routine may also affect susceptibility to disease.

===Types of Agents Causing Disease===

===Types of Agents Causing Disease===