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Introduction to General Pathology (view source)
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==Introduction==
==An Introduction to General Pathology==
* The term '''pathology''' is derived from:'''Pathos''', or suffering and '''Logos''', or reasoning/logic.
* The term '''pathology''' is derived from:
* Pathology is defined as the study of disease including:
* Pathology is defined as the study of disease including:
** '''Aetiology''' - causal factor(s)
** '''Aetiology''' - causal factor(s)
==Lesions==
==Lesions==
* Lesions are the abnormalities or changes seen in living tissues due to disease, and can be observed in:
* Lesions are the abnormalities or changes seen in living tissues due to disease.
** The live animal
** The live animal
** Tissues surgically removed from the live animal
** Tissues surgically removed from the live animal
*** Biopsy/ excision
*** Biopsy/ excision
** Animals soon after death
** Animals soon after death
*** Necropsy, post-mortem examination.
*** Necropsy or post-mortem examination.
===[[Recognition and Description of Lesions - Pathology|Description of Lesions]]===
===[[Recognition and Description of Lesions - Pathology|Description of Lesions]]===
Descriptions of lesions are very important. Whole organs, tissues or individual lesions are described under headings such as:
*# Size
*# Size
*# Shape
*# Shape
===Definition and Type===
===Definition and Type===
'''Disease''' is a definite morbid (illness producing) process, having a characteristic train of symptoms or signs.
* May affect the whole body or any of its parts.
* The disease's aetiology, pathology and prognosis may be known or unknown.
There are two main categories of disease:
*# '''Acute''' - characterised by sudden onset and short duration.
*# '''Acute'''
*#* The outcome of acute disease may be:
*#* The outcome of acute disease may be:
*#** Death
*#** Death
*#** Resolution due to host defence response or clinical therapy
*#** Resolution due to host defence response or clinical therapy
*#** Progression to chronic disease
*#** Progression to chronic disease
*# '''Chronic'''
*# '''Chronic''' - characterised by insidious onset and protracted course.
*#* The outcome of chronic disease may be:
*#* The outcome of chronic disease may be:
*#** Progressive destruction of tissue
*#** Progressive destruction of tissue
===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.
*# '''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
*# The dose
*#** The virulence of the agent
*# 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:
*# Clinical therapy
*# Host defence systems
*#** Clinical therapy
*# '''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.
*#** Host defence systems
*# '''Environment''', for example:
===Types of Agents Causing Disease===
===Types of Agents Causing Disease===
# '''Infectious organisms'''
# '''Infectious organisms'''
#* [[Viruses|Viruses]]
#* [[Viruses|Viruses]]
===Aspects of Disease===
===Aspects of Disease===
There are many aspects of a disease that must be considered in order to understand it in full.
*# '''Incidence''' refers to how much of the disease is present, where the disease is found and in what species is the disease seen?
*# '''Incidence'''
*# '''Aetiology''' refers to the causal agent(s) and includes predisposing factors
*# '''Transmission''' describes how a disease is spread between individuals, and includes the important question 'is the disease zoonotic'?
*# '''Pathogenesis'''describes how the causal agent(s) exert their effect within the body.
*# '''Diagnosis''' - this is reached on considering the clinical history and findings with reference to the clinical examination and the presence of any pathology. Confirmation is reached by monitoring the respone to treatment or by biopsy or post-mortem examination
*# '''Aetiology'''
*# '''Transmission'''
*# '''Pathogenesis'''
*# '''Diagnosis'''
*# '''Prognosis and Treatment'''
*# '''Prognosis and Treatment'''
*# '''Control and Prevention'''
*# '''Control and Prevention'''
==Post-Mortem Examination==
==Post-Mortem Examination==
* Post-mortem examination (PME) investigates the observable structural changes in the animal.
* Post-mortem examination (PME) investigates the observable structural changes in the animal.
* Information relating to the disease within the body or specific tissue is gained from PME.
* Information relating to the disease within the body or specific tissue is gained from PME.