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==Pathogenesis==
==Pathogenesis==
MAP is primarily spread through herds via faecal-oral transmission, contaminated water, in utero and through infected milk and colostrum. Following ingestion of M. paratuberculosis, infection begins in the ileum. Following uptake by the Peyer's Patches, M. paratuberculosis infects macrophages in the gastrointestinal tract and lymph nodes.
MAP is primarily spread through herds via faecal-oral transmission, contaminated water, in utero and through infected milk and colostrum. Following ingestion of M. paratuberculosis, infection begins in the ileum. Following uptake by the Peyer's Patches, M. paratuberculosis infects macrophages in the gastrointestinal tract and lymph nodes leading to a granulomatous inflammatory response.
There are '''three''' stages of infection in Johne's disease.
There are '''three''' stages of infection in Johne's disease.
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.
==Gross Pathology==
==Gross Pathology==
[[Image:johnes disease proliferative ileitis.jpg|thumb|right|150px|Proliferative ileitis in 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)]]
There are many large macrophages (epithelioid macrophages) in mucosa, submucosa and lymph nodes.
There are many large macrophages (epithelioid macrophages) in mucosa, submucosa and lymph nodes.
The mesenteric lymph nodes are pale and enlarged (though not necrotic), and the lamina propria is infiltrated by sheets of macrophages with some lymphocytes. Acid-fast bacteria are found in the macrophages and giant cells, and this is detected by Ziehl-Neelson stain.
The mesenteric lymph nodes are pale and enlarged (though not necrotic), and the lamina propria is infiltrated by sheets of macrophages with some lymphocytes. Acid-fast bacteria are found in the macrophages and giant cells, and this is detected by Ziehl-Neelson stain.
==Diagnosis==
==Diagnosis==