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Johnes disease

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Johne’s disease is a chronic gastrointestinal infection of adult ruminants characterised by diarrhoea, weight loss, emaciation and eventual death.

What is Johne's disease

Johne’s disease is caused by Mycobacterium avium subspecies paratuberculosis, often known as Map, and is a chronic gastrointestinal infection of adult ruminants characterised by diarrhoea, weight loss, emaciation and eventual death. It is not notifiable in Great Britain although it is in Northern Ireland. It has a worldwide distribution.

Consequences of Johne’s disease

The financial losses from reduced milk yield and early culling are significant. In addition the health and welfare of affected animals is compromised. Infected cattle are more susceptible to other diseases such as mastitis and, because they have difficulty maintaining body condition, their fertility is poor. There is the possibility of transmission to humans via contaminated milk. Concern has been raised that mycobacterium avium subspecies paratuberculosis (MAP) may be causing CROHN’s disease in humans as pathology is similar. However various studies have failed to demonstrate a causative effect.

How is MAP spread

Diseased animals pass large numbers of MAP in their faeces, so a single animal can pose a high risk to susceptible animals and to calves in the herd. Diseased animals may also excrete MAP in milk and colostrum. Cattle remain susceptible throughout their lives but are most vulnerable in the first few months of life. Calves may be infected in the womb but are more commonly infected via:

  • drinking contaminated colostrum
  • ingesting dung that may be present on unclean teats
  • contaminated feed; and
  • contaminated environment or water supplies.

How to spot Johne’s disease

MAP is a slow growing organism. After infection, it may be years before the infected animal becomes ill. At the early stages of infection, the only way to confirm whether an animal has Johne’s Disease is to carry out blood tests. These do not detect all infected animals, but at this stage are more likely to identify infection than tests for the organism itself. Signs of the disease are rarely seen before two to three years of age. Generally, there is a period of reduced milk output or fertility well before the animals begin to show signs of advanced disease. These signs include persistent and profuse diarrhoea and significant weight loss, and are seen most commonly in animals at three to five years of age. Once signs of disease have developed, examination of a dung sample through a microscope is a useful way to confirm the diagnosis.