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CASE NOTES

Climate and Disease

Nigel Brown, DV Glen Innes

Posted Flock & Herd January 2023

SUMMARY

This presentation considers not only the meteorological climate as it relates to disease development with the current spectre of anthropogenic climate change but also the financial, political, bureaucratic, social and emotional climates that influence disease development and control.

Introduction

The Epidemiological Triad of Host, Agent and Environment has underpinned veterinary concepts of disease for many years and was taught to UK undergraduates in the early 70's (personal observation). Understanding these inter-related components of disease development remains a critical component of disease control since it enables the most effective control mechanisms to be instituted. However, society superimposes other influences on disease development and control that need to be considered. This paper considers these aspects of disease and climate.

THE EPIDEMIOLOGICAL TRIAD

Essentially the three components of the Triad may be considered as -

From a property perspective, these are the fundamentals used to develop a farm biosecurity plan. And, because the same three aspects can also be taken into consideration when looking at problems with plants or weeds, they enable a producer to carry out a meaningful risk analysis of the livestock diseases, pests or weeds of concern at the same time.

Unfortunately, while the epidemiological triad described above is of value to disease development and diagnosis, society superimposes some significant influences on the environmental aspects of disease and on effective control mechanisms. Not only is there a significant influence being recognised because of changes in our weather, some of which are anthropogenic, but also the financial, political, bureaucratic, social and emotional climates are changing.

METEOROLOGICAL CLIMATE

Climate is the long term weather pattern in an area, typically averaged over 30 years. None of us can be insensible to modern references to "climate change" and, whatever our perspectives on change-over-time and man-made causes, we can acknowledge that climatic changes do occur and will lead to changes in disease in our own areas.

For instance, the rainfall of the last few months on Northern Tablelands has created major disturbances to the usual patterns of parasitic worm behaviour with phenomenal larval survival and egg-laying followed by heavy sheep losses. Tall, thick pasture has further reduced larval death with their protection from UV light and a permanently moist micro-climate down at ground-level. The same tall thick grass has also affected animal behaviour and many producers are commenting on how their sheep are grazing round their camps where the pasture regrowth is providing them with adequate feed in a much smaller area. Epidemiology suggests that the level of pasture contamination with worm eggs and larvae will therefore be much greater when concentrated in this smaller grazing area. At the same time, a significant uptake of 'Barbervax'® (Wormvax Australia Pty Ltd) to control Haemonchus accompanied by inadequate worm-egg monitoring and treatment regimes, has led to unusual but highly significant black scour problems (Trichostrongylus spp).

Similarly, survival of disease vectors such as Culicoides midges and Lymnaea tomentosa water snails will be influenced by local weather conditions both for their survival and distribution and is likely to lead to a surge in dependent disease in the future.

Similar considerations influence the development of so many diseases - mineral deficiencies aggravated by lowered intake in lush and rapidly-growing pastures for example iodine or magnesium, or lack of close grazing reducing significant soil intake for example selenium, toxins from verdant growth, such as blue-green algae on dams, St John's wort, assorted fungal staggers and many more.

While these issues are bread-and-butter to so many of us here today, the result of weather changes is to consider the result when certain diseases become endemic in an area where they were once an occasional arrival. If insect vectors are no longer killed by the frosts of a normal winter, diseases they carry do not disappear with them but remain endemic to the area. In some cases, this may be beneficial in that immunity is passed to newborn livestock every year rather than the notorious outbreak of disease every 7-10 years when immunity has faded. In others this may mean the need for added levels of vaccinal protection and/or fly control.

Now, Australia is certainly suffering a plethora of climatic incidents and the arrival of major livestock health problems. The detection of Japanese encephalitis virus (JEV) a few weeks ago highlights the concern over diseases brought in either by vectors, e.g. insects, birds and wildlife, or by infective particles brought-in on the wind. Transovarial spread of JEV and the presence of wild pigs pose a serious threat to small producers and rare breeds away from the large commercial enterprises. We are probably all familiar with the long-distance migration of waterfowl and their potential as a source of Avian Influenza virus in Australia (Figure 1) but what do we know of the migration of the various flying foxes inside their distribution across Asia. (Figure 2). This would appear to pose a significant risk of transboundary disease spread.

The role of both native and feral animals as a reservoir for infectious diseases is highly significant. The potential for our mammals, birds and insects to become a novel reservoir is possibly as significant as the arrival of traditional vectors because of changing climate.

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Fig 1. Migratory pathways of waterfowl
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Figure 2. World distribution of flying foxes

As a young student just after UK's 1967 Foot and Mouth Disease outbreak, I was taught that infection arrived through windborne spread on the stratosphere from the south of France which was the only place where that strain was present in the world at the time - 1400kms away. In late 1980's, the late Vic Simpson working for MAFF (Ministry of Fisheries and Food) in Cornwall told me over a beer that he had just carried out a post-mortem on a Daubenton's bat (Myotis daubentonii) with clinical signs of rabies (exotic to UK). His investigations confirmed the diagnosis and identified that the bat had flown about 450 kms over the English Channel from France with wind patterns of the time confirming a flightpath from a known outbreak in north-east France to where the animals was found in Somerset.

Following on from previous work by the Bureau of Meteorology, Australia, as well as the Australian Department of Agriculture, Fisheries and Forestry, modifications were made to the HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) source code decision support system to develop an aid in the risk evaluation of airborne animal diseases for Ireland (Lambkin et al., 2019). The system is a computer model that allows integration of atmospheric and disease data such as biological characteristics related to temperature, humidity, lifespan as well as atmospheric washout, and its primary objective is with Foot and Mouth Disease (FMD). Such an atmospheric dispersion system will assist emergency preparedness and aid confinement and eradication strategies during a disease outbreak.

FINANCIAL, POLITICAL AND BUREAUCRATIC CLIMATES

Closely intertwined, the influences of all three are affecting the way different parts of Australian society view livestock disease.

Undoubtedly, the god of our times is mammon. Profit appears to be the driver of many livestock transactions with the science underpinning productivity and performance being barely a consideration. For many producers, the adage 'Where there's live ones, there's dead ones' is alive and relevant with little thought being put into preventative disease control before entry onto a property.

Disease control schemes may be used by some producers, but we are probably all aware of many cases where breakdowns have occurred in footrot, B. ovis and Johne's disease to name three examples of control schemes plus many other diseases where even rudimentary understanding of disease could have prevented significant loss. Despite its broad scope, application of Biosecurity Act 2015 remains weak with elements such as Animal Health certificates and Commodity Vendor declarations not included in the routine psyche of many producers resulting in many animals sold through saleyards, property-to-property and through online sales with inadequate health information being provided to purchasers before they event. This inevitably gives producers the perspective that these are not important.

A classic case occurred on Northern Tablelands during the drought when the manufacturer of a concentrate ration for sheep found grape marc to be a cheap ingredient for his nuts. A ration was formulated and sold but, when yard-fed sheep of several purchasers subsequently died of copper poisoning, it was identified that vignerons apply copper sulphate to grapes to control both insects and parasitic fungi and that grape marc is highly contaminated. The manufacturer had not re-analysed copper content of his new product but sold it under his old label. None of the producers was prepared to support official action against the producer, each seeking individual settlement for losses incurred.

Across the Northern Tablelands, as well as every other LLS region, the reality of rising costs and labour hire means that an ageing workforce is trying to do more work with fewer staff. Standards of stockmanship and animal welfare are falling in many types of enterprise where there are usually inadequate management skills as highlighted during the recent drought. Attempting to buy the cheapest animals or fodder generally means getting those other people want to get rid of along with their imperfections, diseases and weeds. This last year's rain has allowed germination of many unusual seeds in our area which lifelong inhabitants have never seen before.

Throughout my career I have witnessed how many different countries have applied veterinary services and I sincerely believe that the mechanism found within NSW, although not perfect, is the best. By utilising private veterinarians, DPI and a field arm which has evolved from the program created to eradicate sheep scab, through Pastures Protection (PP) boards, Rural Lands Protection Boards (RLPB), Livestock Health and Pest Authorities (LHPA) to Local Land Services (LLS), it provides a widespread cadre of dedicated field staff with eyes and ears on the ground. In far too many states, territories and nations it has become politically and financially expedient to reduce government service and to allow the private sector to provide the necessary service. The UK was in dire straits when FMD reappeared in 2001 with very few veterinarians in government services and inadequate numbers of veterinarians from private practice prepared to work in disease control. Vast numbers of retired and overseas veterinarians were employed. Unfortunately, private service operates for a profit and much of rural Australia would provide inadequate recompense in the private domain were surveillance activities to be carried out by them, although, interestingly, the UK has long used a mechanism of appointing local veterinarians as Local Veterinary Inspectors for specific duties and at set rates.

SOCIAL AND EMOTIONAL CLIMATES

Experience on the Northern Tablelands, both in LLS and among private practitioners, indicates a very real social problem in finding veterinarians prepared to commit to a way of life. Now is not the time to enter a full discussion of life expectations of today's veterinarians and their partners except to suggest that an acceptable occupation and remuneration for both can be hard to find in many towns; one of my close single veterinary friends is intending to leave her practice in search of a partner. The role of a field officer who spends a significant amount of time in surveillance activities investigating disease outbreaks is, I believe, of critical importance in the present climate where there seems to be a greater requirement for clerical activity than ever in my career. Practical skillsets and a desire to work in the field remain critical components of a veterinary field service. It is therefore vital that those training tomorrow's veterinarians ensure that these expectations are met by appropriate student selection (which is frequently not achieved purely on exam results) and that employers continue to base staff selection on field-based criteria.

Conversely, an interesting result of COVID is that many people are wanting to move away from cities for a 'sea change' where they can use modern telecommunications to work from home. This means they can adopt a more rural lifestyle and create 'hobby farms' without understanding the risks of closer proximity to wildlife and disease vectors in areas with fruit-bearing trees, flying foxes, low-lying areas with mosquito activity, feral animals etc. Many diseases, including welfare issues, are often the result of their owners not understanding fundamentals of their animals' biology or disease control.

It is well recognised that the global spread of many infectious agents around the world is exacerbated by the mobility of individuals, albeit limited by COVID at the moment. A significant amount of biosecurity resources is expended in policing not only human traffic but also the vast amount of industrial container, courier and postal movements. In a modern society where user-pays, there is much to be said for visitors to Australia paying towards these services (although I hesitate to use the words 'biosecurity tax') and to increase the levels of inspection of high-risk freight such as international gifts to residents and other mechanisms for the entry of biosecurity matter.

There was much discussion in the UK about the Irish Republican Army (IRA) spreading FMD back in 1967 and, to a lesser extent, 2001 outbreaks. Disease associated with wars has been well-recognised throughout history with movement of livestock and food, for example rinderpest in Europe, and as a deliberate weapon, for example Mongols tossing the victims of the Black Death (yersiniosis) over the walls into a besieged Kaffa in the Crimea in 1347. Gruinard Island in the Inner Hebrides was used to trial a British plan to drop anthrax-infected cattle-cake over Germany to kill the livestock or humans eating their meat. Apparently, the plan was not adopted and, although officially declared free after unbelievable treatments involving formaldehyde and other toxic chemicals, some specialists believe the island remains infected.

Perhaps one of my greatest fears as a veterinarian is that disease control and eradication on a herd or flock basis may require extreme policies such as widespread slaughter. For instance, eradication of Foot and Mouth Disease would be critical for Australia to re-enter the world market. Options include slaughter and vaccination policies but given the recent social unrest in many countries over COVID vaccination, the ramifications for either do not bear contemplation. Widespread social-media exposure is now available for detractors of a slaughter policy and the propensity of some sections of the 'established media' to create dissent and arguments are both far more common than they were for the UK FMD outbreak and it was a growing problem then. It is perhaps inevitable that, were there to be an outbreak of a major notifiable disease with a fatal prognosis either through natural attrition or control strategies, that many owners of 'pets' would attempt to move them to a safer location, thereby risking disease spread, or else defy control measures and become a cause célèbre with immense social and political implications, probably with both legal and illegal activity.

EDUCATIONAL CLIMATE

Given the wide-ranging discussion above, the current educational climate for producers deserves closer examination. Whatever name it goes by, the role of veterinarians within LLS is primarily disease diagnosis and certification and with only a small amount of time given over to education. Problems highlighted by the drought clearly show how many producers and other livestock owners are unaware of many of the fundamentals of biosecurity and the epidemiology of disease, despite their critical importance in Australia's livestock health. There are many erudite and well-informed producers but, as an industry, livestock production needs to find a mechanism to raise levels of awareness and understanding of this critical aspect of our nation's wealth, history and culture. Graduate training provides some of this but, surely, LLS has a significant role to play. While personal communications can require several years for trust to develop, agriculture really needs a pro-active mechanism to provide fundamental knowledge to its players on the ground when so many health problems exist because of ignorance.

Conclusion

While the original Epidemiological Triad remains a valuable concept for disease aetiology and development, disease control is significantly dependent on various aspects of the environment. Not only is the meteorological climate a vital component of this but also the interrelated financial, political, bureaucratic, social and emotional climates of modern Australia.

There appears to be a widespread lack of understanding of the biology of diseases and their control which suggests that appropriate education is required to raise awareness of both underlying scientific principles and specific high-risk or high-profile exotic diseases such as FMD, African Swine Fever (still widely called 'flu'), lumpy skin disease and others.

Is LLS the right organisation to front such a move or should it be the role of other organisation?

As civil servants, there is much to be said for LLS staff to take the lead in the extension of well-known concepts and knowledge to provide a safe farming environment for our producers and a safe product for consumers of our livestock.

References

  1. Keith Lambkin, James Hamilton, Guy McGrath, Paul Dando and Roland Draxler, (2019) Foot and Mouth Disease atmospheric dispersion system. Adv. Sci. Res., 16, 113-117

 

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