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Organisms penetrate the M-cells of the [[Peyer's Patches - Anatomy & Physiology|Peyer's patches]].  
 
Organisms penetrate the M-cells of the [[Peyer's Patches - Anatomy & Physiology|Peyer's patches]].  
 
Mycobacteria invade macrophages and cause a granulomatous inflammatory response.
 
Mycobacteria invade macrophages and cause a granulomatous inflammatory response.
Death may result from:  
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Death may result from: damage to the mucosa, not absorbing nutrients, or inflammatory loss of protein.
** Damage to the mucosa.
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**Nutrients cannot be absorbed.
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** Inflammatory loss of protein
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The infected host appears emaciated.
 
The infected host appears emaciated.
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*** Fat is pale and oedematous, and there is not much of it.   
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Fat is pale and oedematous, and only present in small amounts.   
* 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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Signs are confined to the terminal [[Small Intestine - Anatomy & Physiology|small intestine]] (especially the [[Ileum - Anatomy & Physiology|ileum]]) but are characteristic. It has diffusely thickened, velvety mucosa surface and transverse, corrugated ruggae with reddened crests. Infected animals may also have enlarged mesenteric lymph nodes
** Diffusely thickened mucosa
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*** Transverse, corrugated ruggae with reddened crests.
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[[Image:johnes disease proliferative ileitis.jpg|thumb|right|150px|Proliferative ileitis in Johnes disease (Courtesy of Bristol BioMed Image Archive)]]
**** Cannot extend the gut to remove these (i.e. they are permanent ruggae).
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*** Velvety mucosal surface.
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Changes are milder in sheep and goats, than seen in cows, and is symptoms are often missed.
*** Mucosa may take on a 'corn-on-the-cob' appearance in advanced cases.[[Image:johnes disease proliferative ileitis.jpg|thumb|right|150px|Proliferative ileitis in Johnes disease (Courtesy of Bristol BioMed Image Archive)]]
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** Serosal oedema.
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** Distended lymphatics.
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* Enlarged mesenteric lymph nodes.
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* Changes are milder in sheep and goats.
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** Often missed.
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** May produce small areas of necrosis not usually seen in cattle.
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** Sheep may get a pigmented form.
      
====Histologically====
 
====Histologically====
 
[[Image:johnes disease histological.jpg|thumb|right|150px|Histological appearance of Johnes disease (Courtesy of Bristol BioMed Image Archive)]]
 
[[Image:johnes disease histological.jpg|thumb|right|150px|Histological appearance of Johnes disease (Courtesy of Bristol BioMed Image Archive)]]
* Many large macrophages (epithelioid macrophages) in mucosa, submucosa and lymph nodes.
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** Mesenteric lymph nodes are pale and enlarged (though not necrotic)
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There are many large macrophages (epithelioid macrophages) in mucosa, submucosa and lymph nodes.
* The lamina propria is infiltrated by sheets of macrophages with some lymphocytes.
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The mesenteric lymph nodes are pale and enlarged (though not necrotic), and the lamina propria is infiltrated by sheets of macrophages with some lymphocytes.
* Acid-fast bacteria are found in the macrophages and giant cells.
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Acid-fast bacteria are found in the macrophages and giant cells, and this is detected by Ziehl-Neelson stain.  
** Detected by Ziehl-Neelson stain.  
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** Bacteria act like foreign body producing a type IV hypersensitivity reaction.
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Bacteria act like foreign bodies producing a type IV hypersensitivity reaction.
* Sheep have two different forms.
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Sheep have two different forms:
*# '''Paucibacillary'''
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1. '''Paucibacillary'''; many T cells, and few bacilli.
*#* Many T cells
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*#* Few bacilli
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2.  '''Multibacillary''': Many macrophages, many bacilli in macrophages, and few lymphocytes.
*# '''Multibacillary'''
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*#* Many macrophages
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*#* Many bacilli in macrophages
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*#* Few lymphocytes
      
===Diagnosis===
 
===Diagnosis===
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* Diagnosis is by
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Diagnosis is by; Histology, Serological tests, [[ELISA]] and AGID.
** Histology
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** Serological tests
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60% of cases have lesions in [[Colon - Anatomy & Physiology|colon]] and [[Rectum - Anatomy & Physiology|rectum]] and can be diagnosed by rectal biopsy.
*** ELISA & AGID
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** Culture of organisms
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[[Category:Enteritis,_Bacterial]][[Category:Enteritis, Proliferative]][[Category:Cattle]]
** 60% of cases have lesions in [[Colon - Anatomy & Physiology|colon]] and [[Rectum - Anatomy & Physiology|rectum]] and can be diagnosed by rectal biopsy.[[Category:Enteritis,_Bacterial]][[Category:Enteritis, Proliferative]][[Category:Cattle]]
   
[[Category:Enteritis,_Granulomatous]]
 
[[Category:Enteritis,_Granulomatous]]
 
[[Category:To_Do_-_Clinical]]
 
[[Category:To_Do_-_Clinical]]
 
[[Category:To_Do_-_Max]]
 
[[Category:To_Do_-_Max]]
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