Johne's Disease

Question 1

Aetiology

Answer 1

• Mycobacterium avium paratuberculosis (MAP)
• Resistant to disinfectants and antibiotics
• Survives >1yr on pasture

Question 2

Transmission

Answer 2

• Oral infection (faeco-oral)
• Transplacental
• Via milk or colostrum
• localises in GIT
• Cell-mediated immune response first which may, or may not, eliminate MAP

Question 3

Chronic MAP

Answer 3

• Granulomatous enteritis
• Thickening of intestinal wall, especially terminal ileum
• Protein-losing enteropathy
• Decreased albumin, progressive weight loss, diarrhoea, oedema
• Usually bright and appetent until terminal stages

Question 4

CS

Answer 4

Dairy:
–	Reduced milk yield
–	Increased ICSCC
–	Reduced fertility
–	Poor body condition
–	Usually culled for poor performance

Beef:
–	Poor fertility
–	Small calf born
–	Calf does not do well
–	Poor condition
–	Diarrhoea (very watery, not dark/bloody)
–	Peripheral oedema

Question 5

Dx

Answer 5

– History & CS	
– Serum ELISA *
– Milk ELISA *
– Faecal PCR
– Faecal smear
– Faecal culture
– Post mortem and histopathology (gold standard)

Question 6

ELISA testing (5)

Answer 6

• Serology = Plain tube (red top)
• In clinical cases 80% positive predictive value
• Result given as % positive relative to control
–Positive control is 100%
• Thus values >100% possible (if more severe disease than the control was: more antibody than controlled had)
• Thresholds differ with labs (usually 40-50% for a positive)

Question 7

Other clinical Diagnostic Tests

Answer 7

• Faecal PCR for antibody
– Increased sensitivity
– More expensive

•	Faecal smear Zeihl-Neilsen
–	False negative very possible
–	Look for clumps of acid fasts
–	Faecal culture
–	‘Gold standard’
–	Can take several months
–	Expense (specialised media)

• Post mortem and histopathology
– Generally very reliable in clinical cases

Question 8

Tx

Control

Answer 8

Tx: none- cull

Control:
• Need to communicate well with farmer 
• Farm visit
          – Identify risk areas 
          – Identify risk management
          – Discuss control 
          – This is a long-term issue

Question 9

Spread

Answer 9

On farm:

• Dung: Udder, environment, slurry, water sources
• Milk
• To unborn calf

calves most susceptible

Question 10

• Control

- Management (5)

Answer 10

Test & cull:
– Removal of infectious animals
– Do not retain offspring for breeding – increased risk of being infected
– Prior to calving & manage +ves together

Management:
– Calf rearing
– Cleanliness
– Colostrum
– Replacement milk 
– Pasture / slurry

VACCINATION!

Question 11

Screening

• frequency (3)
• blood (4)
• milk (3)
• PCR (4)

Answer 11

• Blood test all animals > 2 years old annually
• Milk ELISA test quarterly
• ‘Johne’s accredited free’ = 3 x annual clear tests

Blood ELISA:
• Serology = Plain tube
• ~50% sensitivity
• False negatives possible
• After TB test, false positives occur

Milk ELISA:
•Screened quarterly via milk recording
• Less sensitive
• False negatives and false positives

PCR:
• More sensitive
• Useful in areas of high TB test freq
• More expensive
• Used as secondary test in some screening programmes E.g. follow-up to ELISA +ve in low prevalence herd

Question 12

Disease status accreditation

Answer 12

• Level 1: there have been three clear annual herd tests. This is the lowest level of risk.
• Level 2: There has a current clear herd test, but has not yet gained level 1 status.
• Level 3: At the most recent herd test there are reactors in the herd at the level of three percent or fewer.
• Level 4: There has been more than three percent reactors at its most recent herd test.
• Level 5: Those herds without a health plan for Johne’s disease and that do not adhere to the mandatory elements of the health plan are Risk Level 5. This is the highest level of risk and additionally applies to herds that carry out no testing.

Question 13

Control in Beef herds (7)

Answer 13

1. Identify status of breeding cattle
2. Separate into negative and positive cow groups
3. Biosecurity: establish (herd-level) status of animals coming in to herd
4. Hygiene at calving
5. Keep replacements from negative-test cows and from calves that have had less infection-pressure (i.e. calved at grass)
6. Slurry and / or manure management: not on pasture grazed by youngstock; esp slurry from known positives

as same as dairy plus don’t pool colostrum in herds with known Johne’s disease from cows with unknown / positive test status