Animal Health Australia (AHA) coordinates industry-funded projects to manage Johne’s disease (JD) in sheep, cattle, goats and alpaca.
Our projects work to protect Australia’s favourable JD status and reduce the impacts of the disease and its control measures on the livestock industries.
What is Johne’s Disease?
JD is a serious wasting disease that affects various species of animals. In Australia, JD has been found in cattle, sheep, goats, deer and camelids.
JD infections are caused by the bacterium, Mycobacterium paratuberculosis, which live mainly in animal intestines, but can survive in the outside environment for several months.
JD bacteria affect animals by causing a thickening of the intestinal wall resulting in a reduction in the normal absorption of food. The infected animal is hungry and eats, but cannot absorb any nutrients. This results in wasting and finally death. Diarrhoea and bottle jaw are also common signs in cattle.
A number of strains of M. paratuberculosis have been identified and it is recognised that they are all capable of infecting a number of ruminant species.
Johne’s disease in Australia
Australia is in the fortunate position of having relatively little Johne’s disease compared to most developed agricultural countries.
Large areas of Australia are Johne’s disease-free, and a high proportion of Australia’s livestock populations have no known infection.
Australians are actively involved in international organisations and research dealing with Johne’s disease (see International Colloquium on Paratuberculosis).
AHA manages the National Johne’s Disease Project (NJDP), a cooperative initiative of the Australian livestock industries, governments and veterinarians.
Johne’s disease in cattle
Cause of JD
JD is caused by M. paratuberculosis, which lives mainly in the intestines of infected animals. It causes the intestinal wall to thicken and reduces the normal absorption of nutrients from grazing. An infected animal can eventually starve to death.
Johne’s disease may be transmitted between cattle and sheep, where co-grazing occurs and one of the two species becomes infected.
The bacteria causing JD are resilient and can live for a long time in the environment. Research in southern Australia showed that heat and sunlight destroyed the bacteria; under normal summer conditions in paddocks and waterways, around 90% of the bacteria die within 6 weeks. But in moist, shaded conditions, JD bacteria can survive for longer than 12 months.
Cattle infected with JD excrete the bacteria in their manure. The bacteria contaminate pasture and watercourses, spreading infection to other cattle sharing the same paddocks or yards.
Eradicating JD from an endemically infected herd is difficult.
Clinical signs and symptoms of JD
Most cattle are infected as calves but often do not show any symptoms of JD for many years. They are likely to excrete the JD bacteria before developing clinical signs.
The numbers of infected cattle in a herd may start out low, but the rate of infection can increase significantly if JD is not controlled. In addition to the risk of spreading the disease, visibly sick and dying animals can cause animal welfare issues and reduce enterprise production.
The most common signs of JD in cattle are:
- chronic diarrhoea (scouring)
- eventual death.
Not all infected cattle show these signs; some just fail to reach their full productive potential.
First signs of JD in dairy cattle are:
- a drop in milk production
- then weight loss and—in most cases—scouring.
This would occur even though you are feeding the cattle well. Bottle jaw (soft fluid swelling under the lower jaw) can also be seen in the early stages.
First likely sign of JD in beef cattle is weight loss, with or without concurrent scouring.
Johne’s disease in sheep – ovine Johne’s disease
Cause of ovine Johne’s disease (OJD)
OJD is an incurable, infectious wasting disease of sheep that can result in significant economic losses on infected farms due to sheep deaths and lost production of sheepmeat, lambs and wool, when not managed.
OJD is caused by the sheep strain of the bacterium M. paratuberculosis, which leads to the intestinal wall slowly thickening, causing reduced absorption of nutrients from the intestine. This eventually leads to severe loss of condition. An infected sheep can waste away and die.
Sheep infected with OJD excrete the bacteria in their manure, contaminating pasture and water supplies and spreading infection to other susceptible sheep.
Eradicating OJD from an endemically infected flock is difficult.
Clinical signs and symptoms of OJD
OJD is often not diagnosed in a flock until a significant proportion of the flock is already infected and deaths are occurring.
There is often no sign for the first few years, which is why OJD may be referred to as a ‘silent but costly disease’.
Infected sheep can be shedding the bacteria in their manure for a considerable period (sometimes years) even though the flock still looks healthy, but they are contaminating the pasture and infecting other sheep.
The first sign of the disease in a mob is usually a distinct ‘tail’, with sheep ranging in condition from good to very poor, then the sheep in the ‘tail’ start dying.
The number of sheep in this classic ‘tail’ may be constant, but it’s comprised of different animals over time, eroding flock numbers and profits.
OJD-infected sheep continue to eat and drink normally until they are too weak to graze, and eventually die.
Scouring may occur, but is not a common feature of Johne’s disease in sheep.
In some large flocks, the number of deaths may only be appreciated when big discrepancies occur in counts of adult sheep.
When obvious OJD deaths are noticed, the disease is likely to be well established. It will take the producer some years to get the situation under control, during which time deaths will continue.
The best place to look for the disease is in 2 and 3-year olds, but sheep from weaners through to older adults can also die from the disease.
- National BJD Strategic Plan Review
- Disease movement requirements for livestock
- National Johne’s Disease Project (NJDP)
- Johne’s disease in cattle—diagnosis and management of JD
- Ovine Johne’s Disease —diagnosis and management of OJD
- Goat health—includes Johne’s disease management
- Johne’s disease coordinators in Australian states and territories
- Market assurance programs (MAPs) for Johne’s disease