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Johne’s Disease:
An Emerging Issue
for the
Dairy Industry
Lecture 5
Topics
•Organism Involved
•Legal Status
• Prevalence
•Symptoms/Economic Consequences
•Diagnosis/Testing
•Transmission
•On Farm Control
•Processor Controls
•Potential (Unproven) link to Crohn’s Disease
•Implications for Dairy Sector
Introduction
“Johne’s disease is not at all widespread.
It does occur, however, and as the years go
by it will become more and more common
and will places a great tax on the cattle
industry”
Beach and Hastings 1922
Johne’s Disease
- Chronic intestinal tract disease
- Long incubation, 2 to 6 yrs
Causal Bacterium
MAP - mycobacterium (avium)
paratuberculosis
Related to some TB organisms
MAP
• Causes contagious infectious disease (Johnes)
• Causes chronic inflammation of intestine
•thickening of intestinal wall, impairs nutrient
absorbtion
•long incubation (2-6yrs)
•affects cattle, sheep, goats, deer, (wildlife)
•non treatable
Legal Position
• Compulsory notifiable since 1955
• Slaughter of an infected animal or suspected of
being infected (e.g. recent progeny and
compensation)
• Post 1992 - Single Market - unrestricted
importation from Europe (many dairy animals
imported)
• Voluntary import protocol
Prevalence in Ireland
• 1932 - 1982 = 92 animals (mainly imported)
• 1995 = ~7 animals
• 2001 = 54 animals in16 herds (26 from 1 herd)
• 2002 = 100 animals/34 herds (+ 1 herd
depop.)
MAP an Imported Problem
• DVO investigations frequently reveals import
connection
• Random sample (2000)
3 counties, 143 herds
30% herds animal positive (ELISA)
• Research project (2001/02)
1 county,100 herds
> 50% herds showing molecular signal
International Prevalence
•Denmark: almost half herds positive
•Holland: 50 -80 percent herds infected?
•New Zealand 16 - 50
•Imported stock are a high risk
Clinical Symptoms
<5% of infected animals develop clinical symptoms
•Not known what triggers clinical cases (stress)
•Non clinical animals can: can be carriers/shedders
•Symptoms vary - not easy to diagnose
•Intermittent or persistent scouring
•Progressive weight loss/ Drop in milk yield
•Unhealthy appearance/rough coat
•Appetite normal until well advanced?
Economic Consequences -Animals
•Ill thrift
•Reduced milk production (6-16%)
•Increased Mastitis?
•Reproductive performance?
•Premature culling/Increased Replacement Costs
•Lower cull slaughter wt
•Veterinary costs
Diagnosis/Testing/ Vaccination
•Veterinary diagnosis of clinical cases (difficult?)
•Faecal culture: slow (16wks to culture MAP), expensive
•PCR Test (Polymerase Chain Reaction) detect DNA
•ELISA (Enzyme Linked Immunosorbent Assay) detect
antibodies to screen milk or blood - false positives
•Specificity (false positive), sensitivity (False negatives)
Vaccination interfere with TB testing
Transmission primary mode of infection
Ingestion of contaminated faeces from infected
animal shedding M.paratuberculosis:
feed, water, bedding, dirty teats, dirty surfaces etc
Calves most vulnerable to picking up infection
Other Transmission Routes
•Colostrum /Milk if dam has advanced clinical disease
•In utero ( if cow has advanced clinical disease, 20 -50 of
foetuses will be infected)
•Using colostrum from other herds
•Spreading manure from other herds
• Semen?
Contagious, spreads silently over a long time
Severity of Shedding
Advanced Clinical Disease
•Heavy shedder up to 500bn organisms/day
• 36% of clinical cows will shed in milk/colostrum
Light shedders • 9% of samples infected
Survival of MAP Organism
MAP can survive for a long time outside animal
Cattle Faeces: 246 days
Water: up to 17 months
Soil: pH (acidity) seems to be a factor.
Class Exercise
Johnes Risk Assessment
Categorise Irish dairy herds on the basis of their risk of
having Johnes.
Categories:
High Risk
Moderate Risk
Low Risk
Risk Assessment Profile for Johnes
Highest Risk: Herds with imported animals
High Risk: Herds with offspring of imported animals
Moderate Risk: Herds with bought in animals
Low Risk: Closed Herds
Class Exercise
Objective at farm level is to block
transmission from the
MOST infectious to the
MOST susceptible
MOST of the time
Develop a checklist of key control practices to block
Johnes transmission in a dairy herd
On Farm Controls
• Replacement Heifer Rearing/Sourcing
• Infected colostrum or milk
• Ingestion of faecal material
• Housing contaminated with adult faeces
• Pasture used by adults and calves
• Spreading manure on pastures grazed by calves
• Infected water supplies
Replacement Policy
“Keep infection outside”
•Replace from within own herd
• Don’t retain heifers from suspect cows
•Purchase only from ‘clean’ herds
Young Calves (Repl. Heifers)
• Wash cows teats and udder before milking colostrum
• Separate calf from cow as soon as possible after birth
•Clean bedding to minimise faecal contact
•Offer roughage (hay) to stop calves eating bedding
• Avoid contact with faeces from adult herd
Calf Feeding Policy
• Do not bulk colostrum
- dam’s colostrum only
- colostrum from cows with at least 6 lactations
• Do not feed bulk whole milk to replacement heifers
-feed milk replacer to female calves?
Housing and Hygiene
• House calves away from adult cows
• Do not use equipment or utensils which have
been in contact with adult cows to feed
heifer
calves
• Do not allow replacements on to adult cow
pasture
Water Supply
• Adult cattle may infect a pond or stream
- prevent access to such sources
• Provide a clean water supply for all stock
Prevention - Summarised
• Hygiene at calf rearing
• Contact between calves and adult herd
•Not feed bulk whole milk to replacements
•Manage manure
Processor Controls
•Pasteurisation temperature & duration critical
•MAP is a heat resistant organism
•Pasteurisation Regulations: 72 C -15 secs
•Low levels of MAP found in pasteurised milk
•FSAI recommend pasteurisation @72 C -25sec
Is Johnes a Food Safety Issue
Crohn’s Disease is a bowel disease in humans
Overall incidence 5.6 cases per 100,000
Severe and very unpleasant condition
Cause unknown, maybe infectious agent like MAP
MAP (Johnes) organism foundin Crohn’s
No firm link established, evidence inconclusive -but
worrying
Class Exercise
Johnes Control: What are the responsibilities of:
- Department of Agriculture
- Processors
- Vets/Farm Advisers
- Farmers
_
Herd Bio-security
• Bio security – protecting herd health
• Protect against disease and parasites
• Two levels: individual farm
national biosecurity
• Certain diseases/parasites can have major:
economic, financial and food chain
consequences.