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Also known as: '''''Paratuberculosis

| Also known as:

| '''Paratuberculosis

==Description==

==Description==

Johne's Disease is a contagious and chronic disease of ruminants caused by the bacterium ''[[Mycobacterium avium subsp. paratuberculosis]]''. Affected species include cattle, sheep, goats and camelids. The disease is present worldwide with the highest prevalence occurring in dairy cattle. In these animals the disease is responsbile for severe economic losses due to reduced reproductive performance, increased susceptibility to disease, reduced milk production and culling losses.

Johne's Disease is a contagious and chronic disease of ruminants caused by the bacterium ''[[Mycobacterium avium subsp. paratuberculosis]]''. Affected species include cattle, sheep, goats and camelids. The disease is present worldwide with the highest prevalence occurring in dairy cattle. In these animals the disease is responsible for severe economic losses due to reduced reproductive performance, increased susceptibility to disease, reduced milk production and culling losses.

==Pathogenesis==

==Pathogenesis==

''Mycobacterium paratuberculosis'' is spread through herds via faecal-oral transmission, contaminated water and in utero. Young animals less than a year of age are most susceptible to infection and this usually occurs via ingestion of contaminated milk or colostrum. Environmental factors such as overcrowding and poor husbandry may increase the risk of infection.  

''Mycobacterium paratuberculosis'' is spread through herds via faecal-oral transmission, contaminated water and in utero. Young animals less than a year of age are most susceptible to infection and this usually occurs via ingestion of contaminated milk or colostrum. Environmental factors such as overcrowding and poor husbandry may increase the risk of infection.  

Following ingestion of ''M. paratuberculosis'' and uptake by the Peyer's Patches, infection begins in the ileum. ''M. paratuberculosis'' infects macrophages in the gastrointestinal tract and lymph nodes leading to a granulomatous inflammatory response. This leads to malabsorption and a protein-losing enteropathy.

Following ingestion of ''M. paratuberculosis'' and uptake by the Peyer's patches, infection begins in the ileum. ''M. paratuberculosis'' infects macrophages in the gastrointestinal tract and lymph nodes leading to a granulomatous inflammatory response. This leads to malabsorption and a [[Protein Losing Enteropathy|protein-losing enteropathy]].

==Clinical Signs==

==Clinical Signs==

Infected animals may also have enlarged mesenteric lymph nodes.

Infected animals may also have enlarged mesenteric lymph nodes.

[[Image:johnes disease proliferative ileitis.jpg|thumb|right|150px|Proliferative ileitis in Johnes disease (Courtesy of Bristol BioMed Image Archive)]]

[[Image:johnes disease proliferative ileitis.jpg|thumb|right|150px|Proliferative ileitis in Johnes disease (Courtesy of Bristol BioMed Image Archive)]]

==Diagnosis==  

==Diagnosis==  

Diagnosis is difficult, particularly in the case of subclinical disease as there is no single test that will detect all stages of the disease. Bacterial culture is the most definitive test but is time-consuming, requiring up to twelve weeks for incubation.  

Diagnosis is difficult, particularly in the case of subclinical disease as there is no single test that will detect all stages of the disease. '''Bacterial culture''' is the most definitive test but is time-consuming, requiring up to twelve weeks for incubation.  

The most commonly used diagnostic test is the ELISA which detects antibodies to ''M. paratuberculosis'' in clinically affected animals. This is typically used in combination with post mortem and identification of the classic pathological lesions of the disease. Other commercially available tests include baceterial culture, PCR and agar gel immunodiffusion. Test sensitivity may be increased by using different tests in combination.

The most commonly used diagnostic test is the [[ELISA Testins|ELISA]] which detects antibodies to ''M. paratuberculosis'' in clinically affected animals. This is typically used in combination with post mortem and identification of the classic pathological lesions of the disease. Other commercially available tests include bacterial culture, PCR and agar gel immunodiffusion. Test sensitivity may be increased by using different tests in combination.

Diagnosis in sheep may also be complicated due to the disease occurring in two different types in these animals. Multibacillary disease is associated with large numbers of bacteria in the gut and a high antibody response. Paucibacillary disease is characterised by few or no bacteria within the alimentary tract and is associated with a low antibody response. Due to the different type of immune response occurring with each type of disease, there is no single test available to detect the presence of disease. Definitive diagnosis is provided following post mortem exam, histopathology and culture in order to determine the type of disease present.

Diagnosis in sheep may also be complicated due to the disease occurring in two different types in these animals. Multibacillary disease is associated with large numbers of bacteria in the gut and a high antibody response. Paucibacillary disease is characterised by few or no bacteria within the alimentary tract and is associated with a low antibody response. Due to the different type of immune response occurring with each type of disease, there is no single test available to detect the presence of disease. Definitive diagnosis is provided following post mortem exam, histopathology and culture in order to determine the type of disease present.

==Treatment==

==Treatment==

Several studies have reported an improvement in clinical signs following antimicrobial treatment of affected animals. However the same studies have shown that faecal shedding of the bacterium still occurs following treatment, therefore such treatment does not appear to be currently viable. Control measures are aimed at providing good hygiene and husbandry, maintaining adequate stocking densities and minimising exposure of young animals to the organism. Current recommendations include providing clean, manure-free areas for cows to calve and only administering pasteurised or test-negative colostrum to new born calves.

Several studies have reported an improvement in clinical signs following antimicrobial treatment of affected animals. However the same studies have shown that faecal shedding of the bacterium still occurs following treatment, therefore such treatment does not appear to be currently viable. Control measures are aimed at providing good hygiene and husbandry, maintaining adequate stocking densities and minimising exposure of young animals to the organism. Current recommendations include providing clean, manure-free areas for cows to calve and only administering pasteurised or test-negative colostrum to new born calves.

==References==

==References==

* Merck & Co (2008) '''The Merck Veterinary Manual (Eighth Edition)''' ''Merial''

* Merck & Co (2008) '''The Merck Veterinary Manual (Eighth Edition)''' ''Merial''

[[Category:Enteritis,_Bacterial]][[Category:Enteritis, Proliferative]][[Category:Cattle]]

[[Category:Enteritis,_Bacterial]][[Category:Enteritis, Proliferative]][[Category:Cattle]][[Category:Sheep]][[Category:Goat]]

[[Category:Enteritis,_Granulomatous]]

[[Category:Enteritis,_Granulomatous]]

[[Category:To_Do_-_SophieIgnarski]]

[[Category:Expert Review]]

[[Category:To_Do_-_Review]]