What is Bovine Johne’s Disease?

Johne’s disease (JD) is an infectious incurable wasting disease of cattle caused by the C strain of the bacterium Mycobacterium paratuberculosis. It is a notifiable disease in Australia and has been heavily regulated in the past. Most regulations have now been relaxed, with the exception of Western Australia and the Northern Territory.

In Victoria, control of the disease is now managed by individual producers using available tools such as the Johne’s Beef Assurance Score (J-BAS) to profile risk.

In Australia, JD has been known to affect beef and dairy herds, predominantly in the medium to high rainfall zones of southern Australia. The prevalence is higher in dairy herds but beef herds can be affected and this has previously caused loss of interstate trade due to restrictions.

Learn more about changes to Bovine JD Management here.

Impact of Johne’s Disease in Beef Herds

It is estimated that JD costs the Australia beef industry around $2.8million annually (). Individual farm losses vary, but on most infected farms there is little in the way of direct losses. Occasionally, farms with high stocking rates can experience significant mortalities but this is the exception rather than the rule.

Financial losses can be high in herds that require live animal access to sensitive markets like Western Australia, the Northern Territory or some overseas countries.

Losses in individual herds include:

• Death
• Reduced body weight contributing to reduced fertility in the final months of life and
• Potential for a loss of markets in some areas. Although this has reduced recently with decreased regulation.

Different Strains of Johne’s Disease

There are three strains of JD seen in Australia: ovine (sheep), bovine (cattle), and the recently discovered bison strain. Traditionally the bovine strain can be found in beef and dairy cattle of southern Australia while the bison strain have been found in cattle in northern Australia.

Over the last few years more sheep strains have been found in beef cattle to the extent that some areas where cattle and sheep co-graze, more ovine strains are found in beef cattle than bovine strains. Because of this, we no longer refer to Ovine Johne’s Disease (OJD) or Bovine Johne’s Disease (BJD) in beef cattle, just JD.

Clinical Signs

Many infected animals never breakdown with disease. Infected animals usually develop signs of disease after five years of age, which is usually associated with some form of stress.

Infected animals develop a scour that is unresponsive to treatment and gradually waste over three to four months. The affected animal remains bright and alert during this time.

Age-Related Immunity

Infected animals shed mycobacteria in their faeces, with animals showing clinical signs producing the most environmental contamination.

Cattle are usually infected as calves and may develop clinical signs, on average, five to six years later. When or if an animal breaks down with clinical disease depends on the age of infection and the amount of bacteria ingested. Young animals in a heavily contaminated environment tend to break down earlier than animals exposed to lower levels of contamination.

In cattle, a prounounced age-related resistance develops with animals older than one year old becoming much more difficult to infect.

Risk Factors

Beef cattle properties become infected by the introduction of infected animals. In Victoia, dairy cattle and sheep present the highest risk for bringing infection onto a property. Beef cattle can also pose a risk, and risk profiling tools like J-BAS or vaccination can be used to reduce the risk.

Diagnosis

If you suspect JD, a veterinarian will be able to confirm a diagnosis with a blood test, post mortem examination, or faecal culture of PCR.

The available diagnostic tests for JD are of limited sensitivity in young or individual animals but can be quite effective as a herd profiling tool.

Pooled faecal culture (PFC), or High Throughput PCR tests (HT-J PCR), on pools of five samples are the most sensitive tests for screening for JD. Faecal culture can take two to five months with PCR taking around seven to ten days.

The ELISA blood test is reasonably sensitive in animals showing clinical signs but has a lower sensitivity in preclinical infected animals and occasionally may give a false positive.

Vaccination

Silirum® vaccination for JD in cattle is available in Victoria. The vaccine is highly effective at reducing clinical cases and shedding.

In Victoria, Silirum® is currently subsidised for infected herds, at least until the end of 2019. Vaccinated cattle need to be permanently identified with a three-hole ear punch and vaccination status recorded on the National Livestock Identification System. Silirum® may cause cross reaction with TB testing and JD blood testing and treated stock are prohibited from some live export markets because of the potential for false positives in these tests.

Before proceeding with a vaccination program, check the economics of doing so in your herd. The highly reactive vaccine must be administered by an approved vet or under their direct supervision.

Prevention

In Victoria, the greatest risk for JD in beef cattle is co-grazing with sheep or dairy cattle. When agisting or buying stock, biosecurity practices are important to help reduce the risk of JD infection. To assess their JD risk:

• Request an Animal Health Declaration when purchasing sheep or cattle
• Only buy stock with an equivalent or higher J-BAS
• If buying sheep, purchase low risk or approved vaccinates. Remember this may still hring in infection.
• Reduce the chance of strays bringing in infection by ensuring boundary fences are stock proof.

Further Resources

Changes to BJD Management

Agriculture Victoria – Bovine Johne’s Disease

Dairy Australia – Bovine Johne’s Disease

Meat & Livestock Australia – Johne’s Disease

The New South Wales Department of Primary Industries – Johne’s Disease in Cattle

Zoetis Animal Health – Silirum® Vaccine