Johne's Disease

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Also known as: Midges
The most important veterinary species Culicoides


Paratuberculosis/ 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.

    • May be seen in zoo ruminants and goat herds.
    • Particularly prevalent in Channel Island breeds.
    • Is now also becoming a problem in Limousin breeds.
  • Produces a chronic proliferative enteritis.
  • Is usually fatal, since the disease cannot be got rid of.
  • 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.
  • Mycobacterium is excreted in urine and milk as well as in the faeces.

Clinical

  • Clinical signs develop in older cows after calving i.e. 3 to 4 years of age.
  • BUT animals are infected as calves less than 6 months old
    • The disease develops very slowly.
  • Clinical signs include:
    • Ongoing, chronic profuse diarrhoea.
      • Paint like consistency.
    • Hindquarters and tail-caked with faeces
    • Faeces also splattered on walls.
    • Animal gradually fades away and dies over the course of months.

Pathogenesis

  • Organisms get in through the M-cells of Peyer's patches.
  • Mycobacteria invade macrophages and cause a granulomatous inflammatory response.
  • Death results from:
    • Damage to the mucosa.
      • Nutrients cannot be absorbed.
    • Inflammatory loss of protein

Pathology

Gross

Johnes Disease (Courtesy of Bristol BioMed Image Archive)
  • Quite typical
  • Cows appear very emaciated.
    • Depends on how long the disease has been there.
    • Not very much to see!
      • Fat is pale and oedematous, and there is not much of it.
  • Signs are confined to the terminal small intestine (especially the ileum) but are characteristic.
    • Diffusely thickened mucosa
      • Transverse, corrugated ruggae with reddened crests.
        • Cannot extend the gut to remove these (i.e. they are permanent ruggae).
      • Velvety mucosal surface.
      • Mucosa may take on a 'corn-on-the-cob' appearance in advanced cases.
        Proliferative ileitis in Johnes disease (Courtesy of Bristol BioMed Image Archive)
    • Serosal oedema.
    • Distended lymphatics.
  • Enlarged mesenteric lymph nodes.
  • Changes are milder in sheep and goats.
    • Often missed.
    • May produce small areas of necrosis not usually seen in cattle.
    • Sheep may get a pigmented form.

Histologically

Histological appearance of Johnes disease (Courtesy of Bristol BioMed Image Archive)
  • Many large macrophages (epithelioid macrophages) in mucosa, submucosa and lymph nodes.
    • Mesenteric lymph nodes are pale and enlarged (though not necrotic).
  • The lamina propria is infiltrated by sheets of macrophages with some lymphocytes.
  • Acid-fast bacteria are found in the macrophages and giant cells.
    • Detected by Ziehl-Neelson stain.
    • Bacteria act like foreign body producing a type IV hypersensitivity reaction.
  • Sheep have two different forms.
    1. Paucibacillary
      • Many T cells
      • Few bacilli
    2. Multibacillary
      • Many macrophages
      • Many bacilli in macrophages
      • Few lymphocytes

Diagnosis

  • Diagnosis is by
    • Histology
    • Serological tests
      • ELISA & AGID
    • Culture of organisms
    • 60% of cases have lesions in colon and rectum and can be diagnosed by rectal biopsy.