Sheep johnes

Pathogen and transmission

·    Mycobacterium avium subsp. Paratuberculosis

o  Sheep are susceptible to both sheep and cattle strains

Transmission – faeco-oral, via milk/colostrum

·    Subclinical carriers shed bacteria ® infects youngstock

·    Clinical shedders (have ab) ® infects youngstock

History

·    Individual or herd problem? – individual = Johne’s, herd = fluke

·    Previous known incidences?

·    Seasonal problem?

·    What clinical signs?

o  Weight loss?

·    Any scour? – unlikely to be Johne’s if scour

·    Culling rate?

·    What do they do when they find a positive?

Investigations

Clinical exam of affected sheep:

·    BCS

·    Submandibular oedema, brisket oedema

Further investigations:

·    Blood sample for haematology and biochemistry – Johne’s = low albumin (differentiate from fluke – low albumin + globulin)

·    PM exam – granulated/inflamed intestinal lining

·    Serology/ELISA – ab will be low until clinical disease (around 2-3y)

·    Faecal PCR – but intermittently shed

Treatment

·    No treatment – cull

Control

·    Lamb thin/old/high risk ewes away from rest of flock

·    Select replacements from younger ewes

·    Cull low BCS ewes

·    Maintain good hygiene and clean bedding at lambing – reduce faeco-oral transmission

·    Vaccination – reduces shedding and clinical signs (but doesn’t prevent infection)

o  But not used as interferes with TB test results

Issues with control:

·    Low sensitivity of diagnostic tests

·    Hard to detect sub-clinical animals

·    Contact between sheep and cattle (co-grazing, slurry spreading)