Key Points –
– Chronic incurable infectious wasting disease
– Intestinal disease – chronic ill thrift
– Young animals the most susceptible, but a disease of older animals
– Long disease incubation period
– Diagnostic tests are poor and slow
– Significant economic losses through deaths, loss of production (meat, wool). Annual death rates can be up to 25%.
– Largest prevalence of Ovine Johne’s is southern NSW and central-eastern Vic
– There is evidence of cross-species transmission from sheep to cattle
What is Johne’s Disease?
Johne’s disease is an incurable, chronic infectious wasting disease that affects predominantly ruminants (sheep, cattle, goats, alpaca, deer). There are 2 separate strains – a cattle strain and a sheep strain.
Clinical signs in sheep are generally aged 2-3yo, poor doing, with progressive weight loss unresponsive to improved nutrition or drenches, and sudden death. Sheep do not have diarrhoea.
Clinical signs in cattle are generally aged 3-7yo, poor doing, with progressive weight loss and have profuse watery diarrhoea. The disease is more common in dairy breeds.
The bacteria causing Johne’s disease takes up to 12 weeks to culture which means that testing for disease can be a long process. The organism can survive for a long period (just over a year) in the soil. Eradication is difficult.
How do my livestock get the disease?
Transmission is through faeco-oral route (ie. sheep shedding the virus in their faeces that gets ingested by other sheep). 1 sheep shedding the virus can infect 10,000 sheep. Transmission can also occur if teats are contaminated during suckling, or contaminated water or other surfaces.
Johne’s can enter a flock through introduced animals – due to the long incubation period, by the time the disease is diagnosed the original source may be uncertain.
How can I test for the disease?
This continues to be a major challenge.
- Flock tests are better than individual tests
- Faecal culture – dung pellets from >350 sheep, culture in pools of 50. Wait 3 months for a result.
- Blood test – less accurate, need to test more numbers, but simple and quicker result
- Mainly blood test for serology.
- Post Mortems are very useful for detecting Johne’s disease. The veterinarian will be focusing on the gastrointestinal tract and sending parts of the intestines and lymph nodes to pathologists for analysis.
- Abattoir surveillance – cost effective and practical
What can I do to prevent the disease?
- Talk to your veterinarian about the Sheep or Cattle MAP accreditation program to become ‘Monitored Negative’. Repeat testing every 2 years.
- Health Statements – buy or agist stock with a high assurance level
- Dairy enterprise – assess calf rearing strategies, minimise calf scours
- Pasture Management – pasture spelling, lambing flocks on low contaminated pasture, wean lambs onto low contaminated pasture, rotational grazing
- Vaccination for Sheep – ‘Gudair’ – killed vaccine, >90% efficacy with a reduction in mortality and shedding. Single dose at 4-16 weeks of age. There is a high percentage of vaccine site reactions, and there can be serious wounds for humans for 12-18mths when injected
- Early weaning, tight lambing