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==Description==

==Description==

Johne's Disease is a contagious and chronic disease of ruminants caused by the bacteria ''[[Mycobacterium avium subsp. paratuberculosis]]'' (MAP). 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 bacteria ''[[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.

==Pathogenesis==

==Pathogenesis==

MAP is primarily 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 usually become infected through ingestion of contaminated milk or colostrum. Environmental factors such as overcrowding and dirty pens 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 are usually infected via ingestion of contaminated milk or colostrum. Environmental factors such as overcrowding and dirty pens 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.