BJD Frequently Asked Questions

The majority of Australia’s cattle herds are not infected with bovine Johne's disease (BJD). However the disease is currently endemic in the high rainfall zones and irrigated districts of south-east Australia, mainly in dairy herds.

It is not technically feasible or economically justified to eradicate BJD nationally in the foreseeable future. Instead, a national approach to BJD management is being implemented to reduce the spread of BJD to other herds and other parts of the country.

These steps are being taken to reduce the spread of BJD for a number of different reasons:

• Producers who are located in Free and Protected Zones or who have herds in low risk sectors or in the Market Assurance Program (Cattle MAP) want to minimise the chances of their cattle being infected with the disease. This is because they want to retain market access. They may also want to avoid the disease surveillance and control programs that may be required if BJD occurred within their zones or herds.
• Producers with infected herds want to be able to regain market access for cattle and land. The beef cattle industry wants to minimise restrictions on the trading of cattle without compromising the free status of the majority of Australian herds and the possibility of jeopardising international market access in the future.
• The dairy industry wants to protect market access for its products, particularly on the international market.

Many factors influence Johne's disease and its control. Success in managing the disease depends on understanding all these issues and ‘playing to one's strengths’. Farmers need to keep an eye out for opportunities and threats and stay focused on the long-term goal of controlling the disease.

Producers in Australia often raise the following questions about the disease and its control.

1. Are BJD bacteria endemic in sheep, cattle and other domesticated species in Australia?
2. Is managing the disease the best option for JD?
3. Have surveys for BJD ever been carried out?
4. How is the disease spread?
5. Is it true that most beef herds don't have JD?
6. How can you tell the difference between animals that are infected, infectious or diseased?
7. Is it feasible to eradicate BJD with current tools?
8. Is a vaccine available?
9. What action is the rest of the world taking to control BJD?
10. Is it true that the BJD screening test is only 20% accurate?
11. Why is action warranted?
12. Is it true that BJD has only a minor effect on production and health at the farm level?
13. Are cattle with BJD likely to be culled for age before they start shedding the bacteria?
14. How long do the bacteria live in the environment?
15. Who is responsible for making the rules about JD?
16. What is the rationale behind BJD zoning in Australia?
17. Why are there different requirements for stock movements within Australia and internationally?
18. How are vets working on the program able to improve it?

1. Are BJD bacteria endemic in sheep, cattle and other domesticated species in Australia?

BJD is only endemic in the south-eastern dairy industry and in some herds of beef cattle, goats and deer in south-eastern Australia.

It is rare or absent in most of the country, and this restricted distribution is a major factor that is driving the national control of BJD in Australia, and has driven programs by States and Territories for many years.

Johne's disease was first identified late in the 19th century and was first recorded in Australia in an imported bull that was in quarantine in 1911. The first detection in Australian cattle was in dairy cattle in Victoria in 1925. BJD is now endemic in the south-eastern dairy industry. All the evidence to date indicates that it is uncommon in the pure beef industry, in herds where there has been little contact with dairy cattle. But there have been some notable exceptions where beef breeding herds have been endemically infected and, in turn, infected clients’ herds.

Johne's has occurred in goat herds for some time. However much of the endemic infection in the dairy goat industry appears to have been controlled by improved management programs for Johne’s disease (and Caprine Arthritis-Encephalitis or CAE) in the 1980s and early 1990s.

Spread first occurred in alpaca and deer in the 1990s. The alpaca industry encouraged a market-assurance approach and no Johne’s disease has been detected in alpaca since the mid-1990s. Spread from stud red-deer herds has caused concern in the deer industry. The deer industry has supported the development of diagnostic tests suited to deer and a market assurance program, but technical difficulties and a major downturn in the industry have delayed their implementation.

The bacterium causing the disease is cattle-type Mycobacterium paratuberculosis. There is a relatively narrow spectrum of sub-types of Mycobacterium paratuberculosis in Australia and these have differences in their DNA that can be distinguished in the laboratory. Historically, different strains of M. paratuberculosis have evolved that are primarily adapted to sheep or cattle. Although cross-infection from sheep to cattle and from cattle to sheep has been detected in Australia, research and investigations indicate that it does not occur readily. However, it is possible that a strain adapted to both species could evolve here if ovine Johne’s disease (OJD) or BJD was left uncontrolled in a mixed population. The situation will continue to be monitored to determine if it is important in the spread and persistence of infection on farms.

2. Is managing the disease the best option for JD?

Some herd owners want to eradicate Johne's disease so that they can sell breeding cattle or land without restrictions. However, many farmers opt to manage the infection on farm, especially in the dairy industry in regions that are endemically infected. The National BJD Strategic Plan (2008/09–2010/11) emphasises the importance of on-farm management, especially on dairy farms, to reduce the incidence of new infections and the contamination of land and milk.

Calf rearing programs such as the JD Calf Accreditation Program (JDCAP) and the Three Step Calf Plan offer low cost practical means for on-farm management on dairy farms, and have additional benefits for calf health and productivity. Calf management is being incorporated into dairy farm QA programs and can earn points in the National Dairy BJD Assurance Score.

3 Have surveys for BJD ever been carried out?

Animal Health Australia, the Cattle Council of Australia, the Australian Lot Feeders' Association and the south-eastern states put a big effort into a survey of beef herds in south-eastern Australia in 2000–01. Unfortunately the survey had to be stopped in July 2001 because it was not going to meet its agreed objectives.

At that time, about 13 000 cattle had been tested in 81 herds selected for the first stage of the survey.  (A further 17 selected herds had previously tested negative for the Australian Johne’s Disease Market Assurance Program for Cattle [CattleMAP]). Only 19 of the 13 000 cattle, or 0.15%, reacted to the screening ELISA test. This indicated that the prevalence of infection in the tested herds was probably very low. Four of these reactors, in four different herds, were confirmed as infected (one herd being in Victoria and the three others in northern NSW).

The survey had been planned to find out how low the prevalence of BJD was, with a view to easing movement restrictions. Although early results were encouraging, the overall proportion of owners who were participating was only two-thirds of those selected and the rate of testing was very slow.

Surveys have been carried out in other areas (e.g. Western Australia, Queensland, New South Wales) in the past 15 years to better understand their JD situations or to support their claims as low-risk areas.  These surveys have not found infection.

4. How is the disease spread?

Johne’s disease is mainly spread between farms and regions by the everyday movements of domestic livestock.

Where a farm environment is heavily contaminated by faeces from infected animals, any animals in that environment could be exposed to the disease-causing bacteria Mycobacteria paratuberculosis. The level of exposure will influence whether susceptible animals become infected and, in turn, themselves become sources of further contamination.

Where Johne's in farm animals is under control, environmental contamination is greatly reduced. This lessens the risk of any animals becoming infected and further spreading infection, including wild mammals and birds.

The bacteria survive in water for months and even for over a year. Where water is heavily contaminated by M. paratuberculosis, this could lead to infection of susceptible animals that consume enough of it. So, heavily contaminated drainage from infected properties should be regarded as a real risk. The potential for long-distance spread downstream is not known but is thought to be low, as the bacteria are killed by heat and sunlight and have to compete with other microbes.

Work in Scotland has found that M. paratuberculosis was common in rabbits in one heavily-infected region and in animals that preyed on them, including birds. However, contamination rates by rabbits were estimated to be only about one hundredth of the contamination from infected cattle. In Australia several hundred rabbits from BJD and OJD infected properties have been examined without any sign of JD being found. The bacteria can also be found in a range of wild animals in parts of Europe and North America.

Where clinical cases of Johne's disease were found in rabbits in Scotland, the bacteria have also been cultured from the guts of predators and carrion-eating birds, especially crows. The results indicate that, in such circumstances, birds could probably pass bacteria in their droppings and contaminate pasture but very few birds appear to actually become infected.

5. Is it true that most beef herds don't have BJD?

The number of beef herds known to be infected with BJD in Australia is very low, with less than 150 herds currently infected. However, the impact on a business can be severe if BJD is introduced into a beef herd, particularly for herds selling breeding animals. Minimising the risk of this occurring by sourcing cattle from herds that can demonstrate a low risk of being infected is the most effective precaution that producers can take when introducing animals. Herds that are in the CattleMAP , have been tested negative, and those that meet the Beef Only declaration are low risk.

6. How can you tell the difference between animals that are infected, infectious or diseased?

The diagnostic challenge of JD is detecting animals that are sub-clinically infected before they start to become infectious. This is one of the reasons that the Australian program focuses more on herd risk and herd-level assurance.

Animals that are shedding the bacteria in their faeces are infectious and will give a positive result on faecal culture. Many will also be positive on the ELISA test, particularly those shedding large numbers of bacteria.

Animals that are clinically diseased can be shedding billions of bacteria per gram of faeces. Such animals are almost always positive to either the absorbed ELISA or faecal culture tests, or to both.

7. Is it feasible to eradicate BJD with current tools?

The national program and control programs in southern Australia clearly state that they are not trying to eradicate BJD. Instead they aim to manage it in endemic areas and reduce spread to unaffected areas. However there are cases where BJD has been successfully eradicated from individual infected herds and this is an appropriate path to take in those areas and livestock industry sectors (such as alpaca and beef cattle) that have a BJD free or low-risk status.

Since 2004, the Financial and Non-Financial Assistance Program, funded from the Cattle Transaction Levy, has assisted many beef producers to undertake eradication programs on their own properties so as to improve their herd status for trade or other purposes.

8. Is a vaccine available?

A killed vaccine, like the vaccine that is registered for sheep in Australia, is now also being trialled for cattle. As in sheep, the vaccine is likely to delay or dampen down the rate of development of the infection, the rate of shedding and also the rate of onset of clinical disease.

Current vaccines for Johne’s disease are not sufficiently effective to use in non-infected herds in low risk areas in the expectation that they will prevent a herd becoming infected. Australian and overseas research programs will hopefully develop more effective vaccines in the future.

9. What action is the rest of the world taking to control BJD?

During the past decade both the International Dairy Federation and the World Organisation for Animal Health (Office International des Epizooties or OIE) have reviewed the JD situation with a view to achieving more consistent approaches to the management of Johne's disease. In the past five years, two large collaborative research programs have commenced in the USA and the European Community with government funding.

The Netherlands and several states in the USA have had control programs operating in dairy herds for several years, while Sweden has eradicated BJD and Japan is undertaking an eradication program. France has on-farm control programs in place. The USA also has national standards for assurance and control programs overseen by USDA. Canada decided to take a national approach to controlling Johne's disease in 2001.

In The United Kingdom, Mycobacterium paratuberculosis was cultured from approximately 2% of pasteurised milk samples in a survey in 2000. Since then, Food Standards Agency and the Agricultural Department have reviewed Johne’s disease surveillance and control and contamination in milk. Surveillance was found to be inadequate to define the scale of the JD problem and a national prevalence study is now underway. Recommendations were also made on developing tests and the use of herd assurance programs to identify low risk herds and reduce the spread of the disease.

New Zealand is often cited as one country that is similar to Australia but is not worrying about Johne's disease. The New Zealand Government has deregulated its control because it considers that Johne's disease is an endemic production disease that the industry should manage as it sees fit. In contrast to Australia, the disease is widespread in NZ. An economic analysis in 1998 concluded that, for the dairy industry where 60% of herds are estimated to be infected, ‘Johne's disease is a relatively significant disease’ costing about $19 million per annum. Led by the deer industry, the NZ livestock industries have started taking a collaborative approach, with research currently being conducted by the Ministry of Agriculture and Forestry (MAF) and universities.

10. Is it true that the BJD screening test is only 20% accurate?

There are two measures of accuracy related to how good a test is at correctly identifying infected and non-infected animals – test sensitivity and specificity.

Test sensitivity for BJD – that is, the ability to detect infected animals – is low because the growth of the bacteria and development of JD in infected animals is slow. The lower the sensitivity of the test, the greater the number of infected animals that test negative (i.e. a higher false negative rate). Tests for antibodies in blood and for bacteria in faeces are usually negative in the early stages of infection.

A review of the ELISA antibody test in 2000 concluded that, in early infection, the test detected about 20% of infections, and in advanced disease it detected 80%. On average, this review recommended a figure of 30%. A subsequent analysis of the Victorian program indicated that the sensitivity in subclinically infected cows, mostly in seasonal dairy herds, is probably less than 20%.

Test specificity refers to how good a test is at correctly giving negative results for non-infected animals. Johne's tests are highly specific and give very few false positives. In southern Australia, the ELISA usually gives only 2–3 false positive results per 1000 tests. Culture and histopathology should be 100% specific when conducted according to the Australian and New Zealand Standard Diagnostic Procedures (i.e. no false positives).

11. Why is action warranted?

Animal Health Australia has commissioned two economic studies of the costs and benefits of BJD control in recent years, but these have not produced useful cost-benefit indices. This was largely because the models could not predict the rates of spread of Johne's between herds under different control options.

Even though the costs are unknown, Australia has endorsed a national strategic plan for the following reasons:

• Though the evidence to date does not support the theory that M. paratuberculosis is involved in causing Crohn's disease in people, the possibility and the concern that exists in some groups makes it prudent to manage BJD to reduce any real or perceived threats.
• Australia is a major trader in livestock and livestock products in a global market where several of its major markets and competitors are implementing JD control programs.
• The vast majority of Australia and its herds are not infected with the insidious, untreatable disease that BJD is and there is no advantage to them or to the nation for them to become infected. 
• Johne's can cause significant mortality and reduced productivity in intensive management systems if left uncontrolled.
• As aspects of control programs have a negative impact on business and management options for affected herds' assistance measures are needed to support people who are contributing to the national goals by cooperating with the program.

12. Is it true that BJD only has a minor effect on production and health at the farm level?

U.S. research has found that BJD causes milk production losses of about 10–20% and high culling rates in dairy herds as the disease progresses. Under Australian conditions, BJD usually has only a minor effect on production and health at the farm level.  The prevalence of infection within the herd is usually low and it is uncommon to see animals that appear sick in infected herds. However, the rate of infection can increase and visibly sick animals can become more common if Johne's disease infection is not controlled in the herd.

The prevalence of infection in beef cattle is much lower than in dairy herds but some infected breeding herds have experienced sporadic deaths caused by Johne's disease over several years, sometimes in animals that have been sold to clients' herds.

13. Are cattle with BJD likely to be culled for age before they start shedding the bacteria?

Most infected dairy cattle are culled before they break down with obvious disease. However a large proportion of infected cattle do shed bacteria in adult life and can infect calves in the herd. This occurs particularly in infected dairy herds with poor calf management and in infected beef herds with higher stocking rates (especially at calving).  Here the degree of effective contact between adults with advanced infection that are shedding high numbers of bacteria and calves is high enough to result in considerable spread. In Canada, beef herds have as much JD as dairy herds, probably due to concentrated winter calving management.

Although the grazing management in beef herds in Australia is usually not as intensive as in dairy herds, calves are run with adult cattle for much longer. An introduced infected bull can infect the unweaned calves of cows with which he is joined.

14. How long do the bacteria live in the environment?

The bacteria causing Johne's disease (Mycobacterium paratuberculosis) are tough and can live for months – and even for more than a year under the right conditions. But most of these microorganisms do die off fairly quickly in the environment. The main factors that reduce their viability have been identified by recent research in Australia as sunlight and heat. Survival is probably also affected by chemicals and competition with other microbes. Research shows that under normal summer conditions around 90% of M. paratuberculosis bacteria die within six weeks. However in moist shaded conditions the bacteria can survive for over 12 months.

15. Who is responsible for making the rules about JD?

Animal health is a state responsibility under the Federal Constitution. However, JD control operates under several nationally agreed standards which are endorsed by the committee of chief veterinary officers, known as the Animal Health Committee (AHC). This committee meets in person twice a year and more frequently by teleconference. National Johne's policies are developed in consultation with industry groups through AHC's Technical Advisory Group:

• Standard Definitions and Rule (SDRs)
  These comprise nationally accepted minimum standards and practices upon which the states and territories formulate disease control programs to suit their circumstances. Under the SDRs, zoning allows different but appropriate levels of response to infection.
  

• Market Assurance Programs (MAPs)
  These are nationally agreed and audited QA programs for low-risk herds that are managed to reduce the risk of infection and are tested negative. Veterinarians are trained to a national standard and approved for MAPs.
  

• Australian and New Zealand Standard Diagnostic Procedures (ANZSDPs)
  These describe standards for how tests are conducted and interpreted. Laboratories have to be approved to test for JD and participate in regular performance testing of standard specimens that are circulated around these laboratories.
  

National agreement has also been reached in the development of the Beef Only category and the National Dairy BJD Assurance Score. There are also national coordinated and collaborative approaches to JD awareness and communication, and to research.

Most states have BJD steering or review committees that comprise government, industry and sometimes other interested groups or individuals in developing appropriate approaches and plans. Policies will continue to be improved as better information becomes available.

16. What is the rationale behind BJD zoning in Australia?

Zoning is not unique to JD. It is an internationally recognised tool for managing the spread of infectious diseases. Australia has acted to enforce zones quickly for major disease emergencies, such as equine influenza in 2007.

BJD zone classifications are defined under the Standard Definitions and Rules according to the level of infection and the level of disease control that is to be exercised in an area. Before national standards were initiated in the mid 1990s, states and territories took various approaches to JD concerning movement restrictions and quarantine. This has affected the distribution of the disease, and also the control programs applied today; so there are real differences between the states.

BJD zone boundaries are not simply state borders. Zone boundaries must be based on transparent and easily recognised political or physical barriers and the boundaries often do not follow state boundaries. The Control Zone extends from Victoria into South Australia and New South Wales and the Protected Zones then extends north to Queensland and the Northern Territory. In NSW, three coastal districts remain Control Zones because the known level of Johne's disease is too high for them to become Protected Zones. These districts have both recognisable political (Rural Lands Protection Boards [RLPB]) and geographic (mountain) boundaries.

Some political boundaries coincide with effective physical barriers such as deserts and the Bass Strait, so it is logical that state lines be used in such circumstances to separate areas of different risk. Western Australia is classified a Free Zone as it has historically eradicated any episodes of BJD and has recently undertaken surveillance to support its disease-free status. On the other hand, mainland Tasmania has done little to control BJD or survey for it in dairy cattle and is classified a Residual Zone. Flinders Island, however, has demonstrated its low risk status and has recently been declared a Protected Zone (PZ). Like other PZs it will have to take strong steps to control any BJD that is detected there.

What is true is that BJD zones in south-eastern Australia principally reflect the distribution of JD in dairy cattle. The development of the Beef Only declaration has facilitated the movement of low risk beef cattle moving from the Residual and Control Zones northwards into Protected Zones.

17. Why are there different requirements for stock movements within Australia and internationally?

Parts of Australia have a far better Johne's status than most other developed cattle industries in the world so they have sensibly tried to protect that advantage for many years. In contrast, many infected countries do little or nothing to control the spread of infection within their borders and therefore, under international trade rules, cannot justify restricting imports on the basis of BJD status.

The World Organisation for Animal Health (OIE) has wisely deleted its outdated standard for certification from the Terrestrial Animal Health Code.  If, as expected, the future emphasis is on herd or area level assurance risk, Australia will be well placed to enhance its trading position compared to most of our competitors.

18. How are vets working on the program able to improve it?

Under the national Accreditation Program for Australian Veterinarians (APAV), accredited vets can be approved by the Chief Veterinary Officer (CVO) in each state for official programs. These programs involve testing, assigning herd status and certification where the approved vets, in effect, act as agents for the CVO. As such, they are in relatively privileged positions and they undertake to raise issues or provide comments about APAV or about the operational programs with Animal Health Australia or with the particular CVO managing the program in the state or territory.