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===Pathogenesis===
 
===Pathogenesis===
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* Organisms get in through the M-cells of [[Peyer's Patches - Anatomy & Physiology|Peyer's patches]].  
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Organisms penetrate the M-cells of the [[Peyer's Patches - Anatomy & Physiology|Peyer's patches]].  
* Mycobacteria invade macrophages and cause a granulomatous inflammatory response.
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Mycobacteria invade macrophages and cause a granulomatous inflammatory response.
* Death results from:  
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Death may result from:  
 
** Damage to the mucosa.
 
** Damage to the mucosa.
*** Nutrients cannot be absorbed.
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**Nutrients cannot be absorbed.
 
** Inflammatory loss of protein
 
** Inflammatory loss of protein
*** I.e. a [[Protein Losing Enteropathy|protein losing enteropathy]] (hypoalbuminaemia).
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===Pathology===
 
===Pathology===
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====Gross====
 
====Gross====
 
[[Image:johnes disease proliferative enteritis.jpg|thumb|right|150px|Johnes Disease (Courtesy of Bristol BioMed Image Archive)]]
 
[[Image:johnes disease proliferative enteritis.jpg|thumb|right|150px|Johnes Disease (Courtesy of Bristol BioMed Image Archive)]]
* Quite typical
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* Cows appear very emaciated.
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The infected host appears emaciated.
** Depends on how long the disease has been there.
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** Not very much to see!
   
*** Fat is pale and oedematous, and there is not much of it.   
 
*** Fat is pale and oedematous, and there is not much of it.   
 
* Signs are confined to the terminal [[Small Intestine - Anatomy & Physiology|small intestine]] (especially the [[Ileum - Anatomy & Physiology|ileum]]) but are characteristic.  
 
* Signs are confined to the terminal [[Small Intestine - Anatomy & Physiology|small intestine]] (especially the [[Ileum - Anatomy & Physiology|ileum]]) but are characteristic.  
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