Johne's disease in sheep is an infectious and incurable wasting disease. It is caused by the bacteria Mycobacterium paratuberculosis.
Note: The management of endemic sheep disease, Ovine Johne’s Disease (OJD) or Johne’s Disease (JD), change in South Australia on 1 July 2019. For details, see South Australian Ovine Johne's Disease Management Program page.
Clinical signs of OJD
OJD is an insidious and progressive disease. It is not easily detectable and often no clinical signs are evident for the first few years.
Clinically affected sheep progressively lose weight (wasting) and usually die or are euthanised 3 to 8 months from clinical signs being observed.
The classic clinical sign of OJD is a distinct ‘poor’ tail end of the mob.
Due to a long incubation period, healthy looking animals can spread the disease bacteria for some time before becoming clinically affected. A slight increase in deaths and wasting from the disease may not be noticeable initially and may be mistaken for sheep already in poor condition due to old age or having internal parasite issues.
It is likely OJD will already be well established within a flock before deaths are noticed that are obviously attributable to the disease.
The level of disease in a flock is influenced by:
- management practices
- higher rainfall
- higher stocking rates.
Note, once the clinical phase occurs the condition is always fatal.
How OJD spreads between animals
OJD usually enters a flock when:
- new infected sheep enter a flock
- stray infected sheep enter a flock
- sheep eat pasture or drink water contaminated by faeces from infected sheep and other susceptible species
- co-grazing with infected cattle and other species which are infected with Johne's disease (such as goats and alpacas).