Johnes Disease Flashcards
What are the clinical signs of Johne’s disease?
Profuse diarrhoea
Weight loss
Remain bright and eating
Individual animals affected
What are the production losses associated with Johne’s disease?
Clinical cases - loss through culling and production losses Subclinical cases = over 50% of total losses * reduced milk yield * mastitis and high SCC * lameness * infertility * LDAs * increased culling rate
What are the routes of Johne’s disease transmission?
Oro- faecal = major route
Colostrum and milk
In uterus
When is the most ‘at risk’ period of a cow acquiring Johne’s?
Newborn calf between 0-4 weeks
For every clinical case, how many other animals can you expect to be infected and shedding into the environment?
10-25
At what age to clinical signs begin to show and what is the peak age of clinical infection?
Over 3 years of age
Peak age - 5 years
What factor may cause a Johne’s infected cow to switch from a th1 response to a th2 response?
Stress
Describe the pathogenesis of Johne’s disease.
- Infection acquired in early life
- MAP enters macrophages
- Th1 immune response occurs which controls MAP infection
- Stressor occurs
- Th1 response switches to a humoral immune response
- Antibodies are produced against MAP = loss of immune control
- MAP proliferates and the animal is shedding
- Anergy - end stage disease, complete loss of control
What categories of shredders are there?
Low shredders
High shedders
Super shedders
What diagnostic tests are there for Johne’s and what do they tell you?
Faecal culture / PCR - detects shedders
ELISA - detects antibody levels = high probability they are shedding
What is the gold standard test for Johne’s disease?
Faecal culture or PCR
Sensitivity - 50-60%
But takes time and cannot pick up the infected but non-infectious group
What test must you use to pick up the infected but not infectious group of animals?
Gamma interferon test
What is the ELISAs strengths and weaknesses?
Good for detecting infectious animals - good for control
Poor for detecting infected but non infectious animals
- but ELISA inky detects 40% of faecal culture positive animals
How can you change calf management to reduce the risk of calves becoming infected?
Snatch calving Don't feed pooled colostrum Feed the dam's colostrum Clean calving pens Individual calf hutches Keep young stock separate from adults No waste milk feeding
How can you reduce the risk of calves getting Johne’s from colostrum and milk?
Collect colostrum from heifers / young cows / ELISA negative
Feed frozen colostrum
Do not feed pooled colostrum
Pasteurise waste milk and colostrum (25s not 15s for Johne’s)
What are the two strategies of Johne’s control and what must you combine them with?
IMPROVEMENTS IN HYGIENE
- Test and cull
- Test and manage
Describe a test and cull strategy for Johne’s management.
Preform an annual ELISA test on all animals under 2 years old
- cull all positives
- cull all recent daughters of positives
Poor ELISA sensitivity
If not combined with other measures, management is likely to fail
Describe a test and manage strategy for controlling Johne’s disease.
Milk ELISAs are performed 3x a year and cows categorised
Low risk (green) - currently non infectious Medium risk (yellow) - low level shedders High risk (red) - high level shedders
These cows are managed separately at calving
MUST BE WITH IMPROVED HYGIENE
What beef breeds have Johne’s problems?
Welsh black
Limousin
What is different about beef cattle Johne’s management to dairy management?
Pedigree herds have Cattle Health Scheme
If Johne’s free it will be declared on the Cattle Health Certificate
What should you advise a beef farmer when purchasing?
Only buy from low risk herds (CHECS 1)
No history of disease
Test negative on at least 3 occasions
ELISA test the whole herd for bull purchase
How can a beef farmer improve his farm management to prevent to spread of Johne’s?
Outdoor calving
Cull daughters
Clip and clean teats before calving
Ensure bull is free from disease
What should you advise a farmer to do to maintain good biosecurity to keep Johne’s out?
Only buy from clean herds - test negative on 3 occasions
ELISA test whole herd for bull purchase
*testing an individual can lead to false confidence
Vaccinate - reduces shedding, new infections and cases
- 1 to 28 days of age in the brisket
What test might MAP affect?
To testing
Falsely increases the size of the M. avium top lump
How long should you wait between TB testing and ELISA testing?
60 days
How should you manage calves born to shedding cows?
Snatch and wash
Or Euthanise
