What are the intrinsic and extrinsic factors of an epidemic disease?
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Agents associated with disease can be categorized into two broad groups:
· "Living" agents, such as viruses, bacteria, rickettsia, protozoa, helminths, arthropods etc.
· "Non-living" agents, such as heat and cold, water, nutrients, toxic substances etc.
Since infectious diseases of livestock are generally regarded as being of prime importance in Africa, the following discussion is concerned principally with the determinants associated with the so-called living disease agents.
In instances of infectious disease, the presence or absence of the aetiological agent is the main determining factor in the epidemiology of the disease. Obviously, disease cannot occur in the absence of the agent, but, conversely, disease need not always result from the presence of the agent. This leads us to the important epidemiological distinction between infection and disease.
· Infection can be defined as the invasion of a living organism, the host, by another living organism, the agent.
· Disease can be defined as a derangement in the function of the whole body of the host or any of its parts.
· "Living" agents, such as viruses, bacteria, rickettsia, protozoa, helminths, arthropods etc.
· "Non-living" agents, such as heat and cold, water, nutrients, toxic substances etc.
Since infectious diseases of livestock are generally regarded as being of prime importance in Africa, the following discussion is concerned principally with the determinants associated with the so-called living disease agents.
In instances of infectious disease, the presence or absence of the aetiological agent is the main determining factor in the epidemiology of the disease. Obviously, disease cannot occur in the absence of the agent, but, conversely, disease need not always result from the presence of the agent. This leads us to the important epidemiological distinction between infection and disease.
· Infection can be defined as the invasion of a living organism, the host, by another living organism, the agent.
· Disease can be defined as a derangement in the function of the whole body of the host or any of its parts.
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