Johnes

Question 1

what is johnes disease?
What causes johnes?
what is it charaterised by?
what is the course of the disease?
when do animals get infected with johnes?

Answer 1

• Incurable disease of cattle and other ruminants
• Caused by Mycobacterium avium subsp. paratuberculosis (MAP)
• Characterised by wasting and diarrhoea
• Granulomatous enteritis
  Slow/long course:
  infection –> carriage –> sublinical –> clinical (likehood of sheddign bacteria increases throughout this course)

80% of infections occure in frist month of life

Johne’s disease is also known as “paratuberculosis”

Question 2

what human disease has johnes been accociated with?

Answer 2

Crohn’s disease in humans (MAP found in Crohns patients and healthy guts)
Can find MAP in pasteurized milk
Still (currently!) no convincing evidence of causality

Potential major reputational risk to dairy/meat industries

Question 3

what are the sources of infection of johnes?

Answer 3

• faeces from shedding cattle (slurry on pasture can keep pathogen for 6 months)
• colostrum/milk from infected cattle
• faeces from shedd ign goats/sheep (can infect cattle)
• enviroment and fomite spread
• wildlife resrvoirs

Question 4

what are the clinical signs of Johnes?

Answer 4

• Diarrhoea
  
  • Intermittent becoming chronic
• Decreased production
  
  • i.e. milk yield
• Weight loss/emaciation
• +/- oedema (e.g. “bottle jaw”)
• Disease normally develops at 2-6 years of age

Question 5

what are the differentials for Weight loss and diarrhoea?

Answer 5

• Liver fluke
  
  • peripheral oedema
  • very similar clinical apperance to johnes
• Peritonitis
  
  • May find other signs (abdo pain, pyrexia), but not always
  • TRP (“hardware disease”) especially difficult to diagnose, but normally no D+
• Displaced abomasum
  
  • Normally much more acute and with decreased yield more evident/severe, but can be intermittent/chronic
• Abdominal neoplasia - rare
• Chronic salmonellosis - rare
• Parasitic gastroenteritis - rarely causes clinical signs in cattle
• copper deficiency - normally milder group signs (eg infertility)

Question 6

How is johnes diagnosed?
what are the pros and cons of the methods?
when are they used?

Answer 6

• detect MAP in faeces (bacterial shedding)
  
  • PCR
  • directly demonstrates risk of transmission
  • MAP only intermittently shed in faeces, so sensitivity quite poor (20-65%) (better in clinical cases)
  • used as confirmatory test
  • pooled samples occationally used as herd-level diagnostic
• Detect immume responce to MAP
  
  • Currently only detection of Ab In milk or blood
  • Generally higher Se (20-90%) than faecal testing
  • Sp slightly lower (~97 - 99%)
  • cheaper and quicker than faecal testing
  • Blood testing mostly for individual clinical cases and beef herd screening
  • Milk testing commonly used for dairy herd screening - Often uses lower “threshold” for positive

Question 7

how is johnes managed?

Answer 7

individual basis: no treatment, prognosis hopeless, major risk to othe ranimals (esp calves)

Herd level:
Main goal is to minimize exposure of youngstock (< 1yr?) to potential sources of infection
- Slurry
- Colostrum, milk
- Fomites and pasture
- Other species

MAP can survive in the enviroment for over a year
Direct vertical transmission is also possible

Johnes management plan: (needed for many milk buyers)
- know your johnes risk
- know johnes disease status
- create a mangement plan

there are very few johnes naive farms, for these farms biosecurity is the main priority (buying in johnes free cattle is hard)