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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 responsible 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. Subclinical carriers can occur, shedding organisms in their faeces.

==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 an intracellular pathogen that 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|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==

Cattle become infected by the bacteria as calves but do not display the clinical signs of disease until between two and five years of age. In addition animals may be affected subclinically before overt clinical signs are displayed.  

'''Cattle''' become infected by the bacteria as calves but do not display the clinical signs of disease until between two and five years of age. In addition animals may be affected subclinically before overt clinical signs are displayed.  

In the early stages, the disease is characterised by reduced milk production, reduced reproductive performance and increased susceptibility to infection or disease.

In the early stages, the disease is characterised by reduced milk production, reduced reproductive performance and increased susceptibility to infection or disease. There may be intermittent diarrhoea and weight loss.

In the later phases of infection, the clinical signs become more severe. The characteristic clinical signs are of watery 'pipe-stem' diarrhoea and severe wasting (despite maintenance of a good appetite). The disease is progressive and advanced cases may develop submandibular or ventral oedema due to a protein losing enteropathy.  

In the later phases of infection, the clinical signs become more severe. The characteristic clinical signs are of watery 'pipe-stem' diarrhoea and severe wasting (despite maintenance of a good appetite). The disease is progressive and advanced cases may develop submandibular or ventral oedema due to a protein losing enteropathy.  

The disease is similar in goats and sheep except diarrhoea is not a feature.

The disease is similar in '''goats''' and '''sheep''' except diarrhoea is not a feature. It is characterised mainly by weight loss.  

 

It may be rapidly fatal with weight loss and diarrhoea in some '''deer'''.

Lesions are usually localised to the terminal portion of the ileum.  The mucosal surface is diffusely thickened with transverse, corrugated rugae which do not disappear when the intestinal wall is stretched. In sheep and goats however, the lesions usually described are nodule formation with necrosis and calcification .

==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 testing|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.

The most commonly used diagnostic test is the [[ELISA testing|'''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. Separation and isolation of calves from affected dams is also recommended.

 

 

Inactivated adjuvanted vaccines are available and reduce shedding of mycobacteria but do not eliminate infection.

==Literature Search==

==Literature Search==

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

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

[[Category:Enteritis,_Granulomatous]]

[[Category:Enteritis,_Granulomatous]][[Category:Deer]]

[[Category:Expert Review]]

[[Category:Expert Review]]