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)
