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Johne's Disease is caused by ''[[Mycobacterium avium subsp. paratuberculosis]]'', commonly seen in cattle, but known to affect all ruminants.  Common signs include enteritis and diarrhoea.

Johne's Disease is caused by ''[[Mycobacterium avium subsp. paratuberculosis]]''.  This chronic mycobacterial infection primarily affects the small intestine, and is most commonly seen in cattle, sheep and goats.

** May be seen in zoo ruminants and goat herds.

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.

** Particularly prevalent in Channel Island breeds.

 

** Is now also becoming a problem in Limousin breeds.

There are three stages of infection in Johne's disease.

* Produces a chronic proliferative enteritis.

 

* Is usually fatal, since the disease cannot be got rid of.  

'''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.

* Animals may sometimes be carriers without showing clinical signs.  

 

** Once disease is present in a herd, it is very difficult to get rid of it.

'''Stage 2''':  This is again a subclinical infection, usually affecting older heifers, or young adults. Infected animals are apparently healthy, but are shedding infection within their manure, infecting the environment.

* Mycobacterium is excreted in urine and milk as well as in the faeces.

 

'''Stage 3''': Advanced infection. Animals will show clear clinical signs, including weight loss, decreased milk production, and a severe reduction in appetite.

 

Animals with advanced '''stage 3''' will appear gaunt, and the meat is no longer deemed fit for human consumption.  Once the disease is present in the herd, it is ver difficult to get rid of it.

===Clinical===

===Clinical===