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Also known as: '''''Paratuberculosis
Caused by '''''M avium'' subsp. ''paratuberculosis''
Johne's disease refers to the condition caused by the mycrobacterial infection. Calves are most commonly affected by this condition, and can be infected via a number of routes. They may be infected by ingestion of infected manure, or via transmammary infection. In addition, calves may also be infected in vitro, or may ingest the bacteria via colostrum.
==Introduction==
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==
''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.
'''Stage 1''': This often goes unnoticed, as it is subclinical. It typically affects animals less than two years of age, and will advance to stage II, only a few months later.
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]].
The organism is viable in the environment for long periods of time and has a long incubation period with clinical signs appearing in cattle over 2 years of age.
'''Stage 3''': Advanced infection. Animals will show clear clinical signs, including weight loss, decreased milk production, and a severe reduction in appetite.
==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.
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.
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'''.
===Pathogenesis===
==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 sixteen 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.
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.
Other possible tests include:
*Serology of serum including complement fixation tests
*Histopathology of intestines and lymph nodes
*Isolation and identification of mycobacteria from faeces and tissues
*Ziehl-Neelson-positive smears
*Intradermal tuberculin test
*** Fat is pale and oedematous, and there is not much of it.
*DNA probes for detection in faeces
* Signs are confined to the terminal [[Small Intestine - Anatomy & Physiology|small intestine]] (especially the [[Ileum - Anatomy & Physiology|ileum]]) but are characteristic.
* Changes are milder in sheep and goats.
** Often missed.
** May produce small areas of necrosis not usually seen in cattle.
====Histologically====
==Gross Pathology==
[[Image:johnes disease histological.jpg|thumb|right|150px|Histological appearance of 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)]]
Lesions are usually localised to the terminal portion of the ileum. Lymphocytes and macrophages accumulate in the lamina propria and submucosa, resulting in marked thickening and folding of the intestinal wall. 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 .
Infected animals may also have enlarged mesenteric lymph nodes.
==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. Separation and isolation of calves from affected dams is also recommended.
The disease in mainly controlled by slaughter of affected animals, detection and slaughter of subclinical shedders using faecal culture, DNA probes and ELISA.
Inactivated adjuvanted vaccines are available and reduce shedding of mycobacteria but do not eliminate infection.
[[Category:Enteritis,_Granulomatous]]
[[Category:To_Do_-_Clinical]]
{{Learning
[[Category:To_Do_-_Max]]
|literature search = [http://www.cabdirect.org/search.html?it=any&q1=%28title%3A%28%22Johne%27s+disease%22%29+OR+title%3A%28%22Johnes+disease%22%29+OR+title%3A%28Paratuberculosis%29%29+AND+od%3A%28cattle%29&calendarInput=yyyy-mm-dd&occuring1=freetext&show=all&rowId=1&rowId=2&rowId=3&options1=AND&options2=AND&options3=AND&occuring3=freetext&occuring2=freetext&publishedend=yyyy&la=any&publishedstart=2000&fq=sc%3A%22ve%22&y=5&x=67 Johne’s disease in cattle publications since 2000]
[http://www.cabdirect.org/search.html?rowId=1&options1=AND&q1=%28%28title%3A%28%22Johne%27s+disease%22%29+OR+title%3A%28%22Johnes+disease%22%29+OR+title%3A%28Paratuberculosis%29%29+AND+%28od%3A%28sheep%29+OR+od%3A%28goats%29%29%29+&occuring1=freetext&rowId=2&options2=AND&q2=&occuring2=freetext&rowId=3&options3=AND&q3=&occuring3=freetext&publishedstart=2000&publishedend=yyyy&calendarInput=yyyy-mm-dd&la=any&it=any&show=all&x=40&y=10 Johne’s disease in sheep and goats publications since 2000]
|full text = [http://www.cabi.org/cabdirect/FullTextPDF/2005/20053177366.pdf ''' Mycobacterium paratuberculosis/Johne's disease: review & update.''' Whitlock, R. H.; Eastern States Veterinary Association, Gainesville, USA, Proceedings of the North American Veterinary Conference. Large animal. Volume 19, Orlando, Florida, USA, 8-12 January, 2005, 2005, pp 79-80]
}}
==References==
* Jones, T. C., Hunt, R. D., King, N. W. (1997) '''Veterinary Pathology''' ''Wiley-Blackwell''
* Merck & Co (2008) '''The Merck Veterinary Manual (Eighth Edition)''' ''Merial''
{{review}}
[[Category:Enteritis,_Bacterial]][[Category:Enteritis, Proliferative]][[Category:Intestinal Diseases - Cattle]][[Category:Alimentary Diseases - Sheep]][[Category:Alimentary Diseases - Goat]]
[[Category:Enteritis,_Granulomatous]][[Category:Deer]]
[[Category:Brian Aldridge reviewing]]
[[Category:Mycobacterium_species]]