Johnes

Pathogen and transmission

·    Mycobacterium avium subsp. paratuberculosis

·    INITIAL INFECTION (young calves pre-weaning – susceptibility decr. with age) ® CARRIAGE (pathogen in gut, animal clinically well) ® SUB-CLINICAL (some shedding of bacteria, some CS, e.g. decr. production) ® CLINICAL (lots of bacteria shed, more CS, e.g. D+, weight loss)

·    Host response: cell mediated immunity early, then decreases  ® bacteria can proliferate and shed in gut  ® ab response

Sources of infection:

·    Colostrum/milk from infected cattle

·    Faeces from shedding cattle (shed earlier and incr. conc than milk, incr. bacteria shed as dz progresses)

·    Faeces from shedding goats/sheep

·    Environment and fomite spread (persistent in environment)

·    Wildlife reserves – deer, rabbits

History

·    What is their current Johne’s status?

·    Do they routinely test? What do they do if they find a positive?

·    Do they maintain a closed herd or buy in?

·    What’s their calf management like? Snatch calving? Use pooled colostrum?

·    Incidence rate of scour?

Clinical signs

·    Develop at 2-6yr

·    Bubbly D+ - intermittent progressing to chronic

·    Reduced production, e.g. decr. milk yield

·    Weight loss

·    Oedema – brisket, bottle jaw

Investigations

·    Detect MAP in faeces

o  PCR (as culture slow) of pooled samples

o  Shows presence of bacterial sedding and therefore risk of transmission

o  High spec. but low sens. as MAP intermittently shed (risk of false -ves, but sensitivity increases in late clinical dz)

·    Detect immune response to MAP

o  Detecting antibodies (ELISA) in milk or blood – used for individual animal cases

o  Higher sens. but lower spec.

o  Cheaper and quicker

·    Blood sample for serology – low albumin, normal globulin

Treatment and control

·    Clinical cases – poor prognosis, risk to other animals – either cull, or breed to beef stock

·    At herd level

o  Regular bulk milk a/b testing

o  Don’t breed from positive cases

o  Minimise exposure of youngstock to potential infection sources – fomites, pasture, slurry/faeces, milk/colostrum, remove from dam, don’t pool colostrum

·    Prevent spread within farm

o  Regular faeces removal

o  Clean calving areas – calve red/ambers separately to greens, ‘snatch’ calve

o  Reduce fomite spread – border biosecurity, clean PPE

o  Teat disinfection, don’t pool colostrum

o  Maintain closed herd – don’t buy in infected cattle

o  Test colostrum for cleanliness and quality

·    National Johne’s management plan

o  Biosecurity, protect and monitor

o  Improved farm management

o  Improved farm management and strategic testing

o  Improved farm management, test and cull

o  Breed to terminal sire

o  Firebreak vaccination