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CASE NOTES

Plus ça change, plus c'est la même chose

Dan Salmon, retired District Veterinarian

Posted Flock and Herd July 2023
Introduction

The public animal health service of NSW has a proud history of achievement in the control and eradication of infectious diseases in domestic livestock and the control of unacceptable chemical residues.

Sheep scab, sheep catarrh, foot-and-mouth disease, contagious bovine pleuropneumonia, cattle tick, enzootic bovine leucosis of dairy cattle, swine fever, bovine tuberculosis, bovine brucellosis, avian influenza, swine influenza, equine influenza, Newcastle disease and virulent footrot of sheep have all been subject to successful control and eradication programs.

Chemicals such as dichlorodiphenyltrichloroethane (DDT), dieldrin, arsenic and chlorfluazuron produced residues in livestock that caused human health and/or environmental problems and were therefore not acceptable to the market. These chemicals no longer cause any market rejection of livestock products mainly due to the efforts of the NSW animal health service.

On the other hand, there have been some programs that have not been successful. These have ranged from relatively minor wastes of resources to unmitigated disasters with long-term adverse effects.

In considering the genesis and implementation of these programs we might find some guidance in how to avoid repeating the mistakes of the past.

All of the following comments are based on personal experience with only a vague memory for actual dates, so if anyone should be forced to provide a reference for them, they should be attributed to Salmon (2023) pers. comm.

I will look at some of our false steps in the rough order that I came across them.

1. Sheep lice

For much of the 19th and 20th centuries, Australia rode on the sheep's back. At the same time, Australia was not the only passenger on the backs of sheep.

Bovicola ovis, the sheep body louse, was an important parasite that reduced the amount and quality of wool produced, with subsequent severe economic effect. The damage was such that sheep body lice were included in the Stock Diseases Act 1923 as a notifiable disease.

This legislation change was followed by sixty years where significant resources were devoted to inspecting sheep for lice, quarantining flocks detected with lice, inspecting sheep for release from quarantine and prosecutions for breaches of the Act: all with no measurable effect on the prevalence of lice.

In fact, analysis hinted that the number of flocks in quarantine was directly proportional to the number of Inspectors looking for lice.

Eventually sheep lice was removed from the list of notifiable diseases for which quarantine was imposed. There was an uproar: it was quite popular among producers who were not actually in quarantine.

After the furore settled down, life went on. It seemed to me that prior to, as well as following, deregulation of lice, the incidence of infestations rose and fell with the price of wool and whether lice had developed resistance to the latest family of pour-on lousicides.

2. Cancer eye, lumpy jaw and wooden tongue

An interesting group to lump together. It was even more interesting that they were all notifiable diseases for which compensation was paid.

Compensation did seem a little bizarre if one considers the epidemiology of these diseases. None of them were conditions where the removal of infected animals would be likely to change their incidence.

Their inclusion in the list of diseases in the Cattle Compensation Act was a result of the tuberculosis (TB) control program and the robust exchange of opinion that passes to-and-fro across the sandstone curtain.

In the day, cattle compensation was funded by a levy on producers based on the number of cattle that they stated in their Return of Land and Stock to the Pastures Protection Board as well as stamp duty on cattle being slaughtered. Beef producers, particularly those west of the Great Dividing Range, made the case that TB was a disease of dairy cattle on the coast and their levies would be subsidising coastal dairy farmers. This conclusion was later found to be not as definite as it seemed at the time.

So, to pacify some sectors of the cattle industry, it was deemed necessary to pay compensation for cattle with cancer eye, lumpy jaw or wooden tongue. These conditions, that were ubiquitous if sporadic, presented little risk to other cattle and could be treated with surgery or antimicrobial therapy. The trade-off was funding to pay compensation to remove TB reactors that could have continued to spread infection for some years, infecting humans as well as other cattle.

When cancer eye, lumpy jaw and wooden tongue were removed from the Cattle Compensation Act list, all three conditions faded to obscurity and were controlled by breeding and antibiotics.

3 Bovine brucellosis

The Bovine Brucellosis eradication program was very successful.

It was aimed at a disease that caused significant production losses, produced serious disease in humans and was foreshadowed by our overseas markets to be a trade barrier.

It was a national program with strong industry support and a robust funding model.

What could go wrong?

Most of the problems were minor and easily fixed, but the program started off with a major miscalculation.

Because infected animals could live for years and calve normally while spreading infection, any beast that reacted to the blood test was fire-branded with 'R' on the withers.

When abattoir workers became aware of the fact that these animals were infected with a disease that was a major occupational health problem in the meat industry, they refused to slaughter them.

The result was a period of several years during which the reactors continued to spread the disease. The impasse was resolved by an ex-gratia payment of $25 for each reactor killed. It was not bad money for a breeding cow in the day, so most of the reactors were rendered for meat meal.

4 Bovine Johnes disease (BJD)

At the beginning of my professional career, BJD was thought to be a disease confined to Channel Island breeds of cattle with three known infected herds in NSW: one on the South Coast and two on the North Coast.

The official approach to BJD in those days was a little conflicted. It was a notifiable disease and compensation was payable for infected animals. It was recognised that the technology of the time had little to offer by way of control and so no real action was taken in the infected herds.

As time passed and more infected herds were identified there was concern in the cattle industry and the official animal health services across Australia about the spread of the disease. Predictably the level of concern was directly proportional to the local prevalence: the representatives of the beef industries of Queensland and Western Australia, where the disease had never been diagnosed, were the most concerned while the representatives of the dairy industry in Victoria, a hotbed of infection, were the least concerned. Because the prevalence in NSW varied by region and sector the level of concern also varied.

Controls on infected herds in NSW increased progressively until they were all placed in quarantine and prevalence zones were proclaimed.

The dynamics of zoning were interesting, calling to mind the domino theory of the spread of Communism in Southeast Asia in the 1960s.

Queensland, believing their cattle population to be free from BJD, proclaimed the state to be a Protected Zone. Producers in northern NSW saw their markets being affected, so they agitated to become Protected. Producers in central NSW and then southern NSW also sought Protected status.

There was a flurry of activity, with the Market Assurance Program being developed. It had two drawbacks: it was expensive, and there was a risk that previously unidentified infection would be diagnosed.

Predictably the industry separated into three camps:

The activists in the first two camps had quite robust discussions as to the relative merits of deregulation of the disease versus maintaining a rigorous control program.

The matter was resolved when BJD was diagnosed in Queensland with evidence of significant opportunities for the disease to have spread. This detection reduced the value of BJD as a non-tariff trade barrier and the new approach to BJD followed.

Cattle producers now manage their own risk to BJD. Predictably the results vary, but they all have the tools to reduce the risk of introducing the disease and limit the economic impact of the disease if it is present.

This management approach seems to be working and will only be subject to change if BJD becomes a public health or international trade issue.

5 Ovine Johnes disease (OJD)

The OJD program was one of our less successful control programs.

It cost a lot of money, alienated a significant number of sheep producers, caused a lot of quality animal health professionals to leave the sector and did little to control the disease.

If, at the beginning, we had the testing and surveillance tools that we have now, we could have made a better fist of it.

On the other hand, if we had known that the vaccine was as effective as it turned out to be, we almost certainly would have gone straight to a management approach.

When the first cases of OJD were diagnosed in the Central Tablelands of NSW in 1980, consultation between the sheep industry, the Department of Primary Industries and other stakeholders resulted in the decision to not make any official response to the disease. This decision was based on the fact that OJD was a relatively minor disease in other parts of the world, there was no reliable test and that there was no available strategy to combat the disease.

Like many pests and diseases before it, OJD found Australian conditions and sheep much more suitable for its development and spread than had been the case in other parts of the world.

As OJD spread and the losses began to mount up there was a push from the sheep industry to do something about it. This push came from the producers in the areas where the disease was common who wanted to control the spread, producers in areas where the disease had not been diagnosed who did not want their flocks to become infected and a somewhat more cynical group who saw a competitive advantage for their sheep over sheep from areas of higher prevalence.

Once the program started, it quickly acquired a life of its own: a frenzy of testing, tracing, quarantine, and the usual interstate movement restrictions.

There was a lot of high-quality research activity, off the top of my head:

Despite everything, the disease continued to spread inexorably. It became an important limitation on production in areas where the climate and topography suited it. In other areas disease was less aggressive. Whether differences in disease expression by environment were because the disease spread much less aggressively in those environments or because the type of sheep bred in the endemic areas were less suited to the environment and therefore less likely to be moved into the low-prevalence regions remains a topic of robust discussion.

While diagnostic tests and control measures improved there was an active program in some sectors of the sheep industry to deregulate, which was ultimately successful. The efficacy of the vaccine has reduced mortalities to an acceptable level and producers who do not believe that their flocks are infected have tools available that may reduce the risk of their flocks becoming infected.

As usual there was plenty of blame to go around:

The end result was a loss of confidence of many sheep producers in the public animal health service, many good professionals left the service, and the management of the service became gun-shy at the prospect of trying to do anything.

Discussion

In his novel Anna Karenina, Leo Tolstoy stated: "Happy families are all alike; every unhappy family is unhappy in its own way".

The same could be said for disease control programs.

Despite the multifaceted ways in which we can blunder, there are a few themes that can reduce the risk of repeating past fiascos, or at least limit the extent of disaster.

In my view the most important components are risk management, epidemiology and communication.

Risk management is relatively easy once a risk has been identified, it is just a matter of estimating likelihood and consequences. The real difficulty of risk management is to identify the possible risks. It now seems obvious that at a time when a significant number of abattoir workers were sick with brucellosis the industrially active unions of the day would have something to say, but that did not enter the 1970's risk profile.

Arthur Wellesley, the first Duke of Wellington, said: "Time spent on reconnaissance is seldom wasted", and that applies as much to disease control as it does to warfare.

If we'd had a good handle on the prevalence of sheep lice or OJD it is likely that there would have been a different approach.

Any attempt to regulate a disease should be accompanied by a rigorous epidemiological review. It is my view that surveillance must be a well-designed program of active investigation.

In my opinion, passive surveillance is frequently unreliable. William Wright, a 19th Century clergyman, said: "The absence of evidence is not evidence" and this is especially true if one considers the tolerance of Australian farmers to loss alongside the suspicion of the official animal health service that follows failed control programs.

Then there is communication. It is vital every step of the way. It must go in all directions so that every significant stakeholder feels as if they have a stake in the program. If they are being ridden over roughshod, they must at least know that they have had the opportunity to make their case and have it seriously considered before it was rejected.

For any major project the vast majority of stakeholders must share a vision of what the outcomes of the program are and the actions that are likely to be necessary to achieve them.

One of the problems with stakeholder engagement is the difference between doing things and getting things done. Taking the time and effort to determine the outcomes that stakeholders want rather than the activities that they believe are needed is a very constructive communication exercise. At the same time, it is important to have robust two-way communication: letting industry know what we are achieving as well as finding out what they think about it.

The communication program for OJD had a lot of very good features, it was unfortunate that by the time it was rolled out, attitudes had hardened so that no level of communication seemed adequate.

I have not mentioned compensation. There is an eminent body of opinion that adequate compensation is a vital component of any successful animal disease control program. I do not agree that it is essential.

In programs such as the brucellosis and tuberculosis eradication campaign and various responses to exotic disease incursions it was nice to be able to throw money at a disease until it went away. On the other hand, the footrot control program never had a compensation component: producers saw the value in getting rid of infected sheep (or flocks) because the vision of not having to contend with footrot, sometimes for the first time in generations, was so appealing.

That is not to say that it is reasonable to order the destruction of apparently healthy animals without adequate compensation, so in many cases it is essential, just not all of them: the big issue is a shared vision of disease control.

There is also the sad fact that the word 'compensation' seems to be a trigger for some producers. It is amazing how the pedigree and production of an animal seems to increase on an almost logarithmic scale if there is a chance that the taxpayer will pay to have animals killed, even if they are likely to die fairly soon anyway.

A further complication is the fact that the Australian Constitution prohibits States from raising excise, which is the simplest way of raising money for compensation. This limitation means that compensation is likely to be confined to national programs in the future. There was an attempt to fund OJD in a way that would be less likely to stimulate a High Court challenge, and to be honest, it was a dog's breakfast.

Despite knowing the components of a successful program, we should not allow the good to be sacrificed to the perfect. Samuel Johnson said: "Nothing would ever be attempted if all possible objections must first be overcome". Any attempt to control a disease involves a massive learning curve. The tests, surveillance and vaccination for OJD would not have been achieved anywhere nearly as quickly, if at all, if there had not been an official program.

That is important. The OJD program may have been a disaster, but something had to be done. Over a 50-year period in disease control the only times that I have seen farmers in tears on stage was when they were telling us how their hoggets died of OJD.

The downside is that if you do it right, the knowledge that you gain will be worthless and I have found that by the time I start to understand a disease it disappears on me.

 

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