JOHNES DISEASE

Jeff Fyffe BVSc MRCVS MACVSc

 
 

Johnes disease is an enteritis of cattle, sheep, goats, alpacas and deer. Other wild ruminants are also susceptible. It is often referred to simply as JD for short.

The disease causes slow emaciation and in cattle chronic diarrhoea is also a common symptom.

JD is caused by Mycobacterium paratuberculosis but several different strains are known to exist. The sheep strain differs from the cattle strain and it is very difficult to grow in the laboratory.

JD occurs in all temperate climates of the world where the moisture levels are constant. It can occur in some tropical areas.

Deer are susceptible to both the cattle and sheep strains.

The Disease In Cattle and Sheep

Cattle become infected at around 30 days of age but clinical signs do not show until after they are 3 years old with older stock resistant to the infection.
Sheep may become infected at any age but the disease is not apparent until at least 2 years of age.
The disease is acquired by eating food or water contaminated by the faeces of diseased or carrier animals.
In cattle emaciation, swelling under the jaw, “pea-soup” diarrhoea dehydration and weakness are all seen at various stages of the disease. Sheep, however, show weakness, emaciation and often soft un-pelleted faeces. The emaciation that occurs in all animals is due to the loss of protein from the body into the bowel.

The Disease In Deer

In deer JD has a variable onset from a slow insidious wasting disease to a rapid progressive disease and a rapid death. The disease can develop from one year of age. Nothing is known about the resistance of older stock. Weight loss is the most common sign while diarrhoea is less common.
Affected animals retain their winter coat and develop patchy hair loss.
The disease can be confused with any chronic wasting disease including liver fluke, intestinal parasites, lungworm, cancer, intestinal obstructions and mineral deficiencies (particularly copper deficiency).

In the United Kingdom the disease is particularly virulent and can be difficult to control or eradicate.
In New Zealand, by contrast, the disease is present on a relatively low number of farms despite the high sheep population.
These three observations suggest that there may be different strains of JD in the three countries.

Environmental Contamination

The bacterium Mycobacterium paratuberculosis, survives well in cool moist conditions for up to 12 months. After ingestion some animals will become resistant to the disease but will continue to excrete the bacteria in their faeces - these are known as carrier animals.
When stressed these carrier animals may relapse and develop JD.

Treatment

There is no cost effective treatment. The disease MUST BE NOTIFIED to the relevant Agricultural Departments in Australia.

Vaccination

Vaccination is only used in heavily infected cattle herds in Victoria and in high incidence sheep areas in New Zealand. Vaccination will not prevent infection of animals - it only stops the development of clinical JD. Vaccinated animals still carry live organisms.

Diagnosis

The diagnosis of JD in cattle is based on clinical signs and the finding of the causative organisms at autopsy. It takes up to FIVE months to grow Mycobacterium paratuberculosis in the laboratory from either faeces or autopsy samples.

Only 50% of cattle faecal samples will give a positive growth even though the animals are infected.
There are several blood test available as well as a skin test ( similar to that for tuberculosis) available.
Each type of blood test has its good and bad points in that some are more sensitive than others and false positive results can be obtained. This means that the blood test will show positive even thought the animal is actually negative.

In sheep less than 10% of infected animals will produce positive growth when the faeces are tested.
This then provides us with a problem in deer since they can have either cattle or the sheep strains of Mycobacterium paratuberculosis.
The disease is NOT transmissible to humans.

Should Australia Be Concerned?

The short answer is “Yes”.  If present it would cause considerable difficulty for individual farmers as well as considerable economic loss. Any animal that shows loss of weight that is unresponsive to treatment should be submitted for autopsy and diagnosis.

Johnes Disease Control Program

A national program to control further spread of ovine Johnes disease in and by susceptible species (sheep, goats and deer) has been instituted.
Fallow Deer are exempt from the “susceptible species” list since there has never been a reported case of JD in this species.

The National Ovine Johnes Disease Committee has been established comprising the Wool Council, Sheepmeats Council, Goat Industry Council and the DIAA.
The National OJD Program will commence in 1988. Disease Control Zones with movement restrictions are to be introduced. The system of zoning will have no effect on animals going to slaughter.

Movement of susceptible species between zones will require herd testing, either by Enhanced Vendor Declaration (EVD) involving testing of a sample of 50 animals by an approved Veterinarian, or by participation in a Market Assurance Program (MAP). The MAP will cover both bovine and ovine strains.

Eradication of ovine OJD from Australia is the long-term objective, subject to demonstration within the next six years of the effectiveness of decontamination of land by destocking.
The DIAA has agreed to remain in the National OJD Program until 2003 unless there is clear evidence that Australian deer herds are infected with OJD.

Zones

There will be two basic zones:

  1. Control Zone defined as an area thought to be free of the disease but subject to ongoing testing and eradication.

    2.  

     

  2. Protected Zone defined as 100% of properties and 100% of animals known to be JD free.
There is to be no movement of stock from a Control Zone to a Protected Zone without an EVD or MAP except for slaughter.

Zones In States By 1998