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CASE NOTES


Surveillance for changing endemic diseases

Are we using the passive surveillance from District Veterinarians and private veterinary practitioner disease investigations to best manage changes in endemic diseases in NSW's extensive grazing industries?

Shaun Slattery, District Veterinarian, North West Local Land Services

Posted Flock and Herd July 2023

In recent decades, a risk assessment approach to priority setting for public animal health has resulted in a focus on surveillance to maximise the early detection of Emergency Animal Diseases (EADs)1. EADs are generally exotic diseases that have the potential to cause a serious loss of market access, or a large-scale epidemic of national significance. They also include some diseases already present in Australia that have market and/or zoonotic implications2.

The NSW DPI Strategic Plan 2022-20303 reflects this priority setting, with three of the four of the Biosecurity strategic components directed at EADs and their plant and environmental equivalents. Likewise, the LLS State Strategic Plan 2020-20304 has its three listed Biosecurity services similarly focused (the fourth is Animal Welfare). This focus flows to the various subservient Animal Biosecurity plans and agreed policies and procedures. It is also apparent in the DPI Animal Biosecurity staff structures, team naming and current priority programs.

This approach is entirely appropriate and could be justified alone on the current ABARES estimate that a large multi-state foot-and-mouth disease outbreak would have a direct economic impact over 10 years of $80 billion5.

Key investments to maximise the early detections of EADs are the state-wide network of District Veterinarians and the NSW Animal and Plant Health Laboratories (APHL). These are funded through landholder LLS rates and state government funding respectively. They are a major investment, and maximising returns on this investment is a reasonable expectation of both the NSW government and industry.

While the priority purpose of the District Veterinarian surveillance network and the APHL is to ensure the early detection of EADs, the overwhelming majority of investigations performed by District Veterinarians and testing by the NSW APHL (including for private veterinary practitioner investigations) where EADs are excluded lead to the diagnosis of an endemic disease. Of the endemic diseases, again a very high proportion of diagnoses are for unregulated, non-market impacting diseases.

The author suggests that NSW could maximise the value of this 'side product' of EAD surveillance by implementing coordination, analysis and communication to industry and livestock managers on changes in endemic disease occurrence and distribution.

A focus on changes in endemic diseases of extensively grazed livestock is suggested as: there is potentially the greatest benefit to industry through adjustment of existing industry extension services and practices; individuals and industries do not have access to information on endemic disease detection at the state level; and passive surveillance data is generated by the District Veterinarian surveillance network and submissions to APHL by private veterinary practitioners. The author contends that passive surveillance, while having well-known limitations for accurately determining disease incidence, is very well suited for estimating changes in disease incidence, both regionally and over NSW as a whole.

Australia already has robust and industry-funded programs for major endemic diseases. These include both research and extension. Examples include the Paraboss and associated websites6, development of new vaccines7 and the AWI Flystrike Extension Program8. These work well where livestock enterprises are managing known and established diseases for their region. However, significant preventable losses often occur when there are changes in endemic diseases and livestock managers take too long to implement the appropriate management. That is, there are losses that could be prevented by appropriate notice to industry and livestock managers of new endemic disease risks.

The potential gains to the NSW livestock industries are significant. MLAs Priority list of endemic diseases for the Australia red meat industry — 2022 update9 found the Australian cattle industry has three conditions each causing over $100M per year in losses and another seven causing $50-100M each year. Similarly, the Australian sheep industry had seven conditions causing greater than $100M per year and another three causing $50-100M each year. Another 18 conditions across both industries cause significant losses.

With climate change we are entering a period of increasing degree and speed of change in endemic diseases. Not only does climate change shift the regions where environmental conditions are suitable for an endemic disease, there will be changes within livestock grazing enterprises in response to climate change that will generate its own set of changes to endemic diseases.

Modern agriculture, like all industries, has an increasing rate of change. We are seeing changes to enterprises (e.g., movement to meat sheep breeds) and use of new technology (e.g., increased use of self-feeders, new pastures, and fodder crops). We are seeing new disease treatments and preventatives that have largely eliminated some conditions, while also seeing the failure of previous key products due to resistance.

Thus, endemic diseases are increasingly changing in their incidence and presentation, including susceptible animals, favourable environmental conditions, clinical signs, and pathogenicity. These changes can be regional, with a disease either previously unknown or rarely serious in a region becoming common. Movements in external parasites linked to climate change are one example. In other cases, changes in the organism, livestock genetics or enterprise management see endemic diseases change across broader areas, for example the spread of Theileria strains more likely to cause disease.

To prevent losses, industry needs to have notice to adapt their programs and individual livestock managers need to receive suitable advice on new conditions. In some circumstances, new strategies or technical solutions may need to be developed.

The reverse is also true with some conditions no longer causing serious economic loss.

Significant historical examples of changes in endemic diseases include:

It is appropriate for government to deliver this endemic disease surveillance as there is a market failure similar to EADs, with neither individual livestock enterprises nor industry able to deliver this function. Further, industry is already contributing significantly through LLS rates and payment for endemic disease testing at the APHL.

As mentioned above, the DPI Strategic Plan3, has three of the four Biosecurity strategic priorities directed at emergency pests, weeds and diseases. The fourth strategic priority is 'Work in partnerships to minimise impacts to primary industries and the environment from endemic biosecurity threats'. Unfortunately, none of the nine deliverables address surveillance for endemic livestock diseases. This emphasis is reflected in the policies and procedures on management of significant endemic diseases15,16 with a focus on notifiable diseases.

Likewise, the Local Land Services State Strategic Plan 2020-20304 does not address surveillance for endemic diseases.

This prioritisation has led to the current situation where large numbers of livestock disease investigations are conducted and then recorded in the Livestock Health Management System (LHMS) by District Veterinarians and Biosecurity Officers, but there is no coordinated epidemiological assessment of this very large and unique dataset. In 2022, 3,076 Animal Disease Investigations were recorded in LHMS17.

A process for delivering information about the occurrence of endemic disease of livestock in NSW could be implemented without significant diversion of resources away from EADs. Any investment would be a few percentage points of that already invested in the District Veterinarian network and APHL. Further, greater use of the LHMS surveillance data and closer ties to industry and landholders could enhance the ability of DPI and LLS to respond to any major EAD. It would raise the recognition of the District Veterinarian network, APHL and DPI epidemiology capacity, improving EAD surveillance objectives. Finally, invaluable skills for EAD response could be developed through the use of surveillance data for endemic diseases. These include case management systems, epidemiological analysis, decision making and communication to all levels of industry.

A reporting system for reporting on the occurrence of endemic diseases should include the principles of: using both qualitative and quantitative intelligence; ensuring there are clear and known responsibilities for staff and organisations delivering parts of the program, including a program lead; focusing on the priority endemic diseases identified by the MLA but with opportunity to include identified regional priority endemic diseases; and strong engagement with industry at all levels from individual enterprises to industry research and extension bodies including MLA, AWI and academia.

The system requires the following:

The use of risk assessment to manage hazards is a two-stage process. The first step requires considering potential impacts and likelihood. While the potential impacts of changes in endemic diseases are far less than EADs, they are far more likely to occur, particularly in the face of climate change. The second step is the proportionate application of resources to minimise impacts. The minimal additional resources required to monitor for changes in endemic diseases suggests risk assessment would find we are underfunding endemic disease surveillance.

References

  1. NSW DPI Policy - Biosecurity - Management of animal biosecurity in NSW www.dpi.nsw.gov.au Accessed April 2023
  2. Animal Health Australia, EADRA p4 www.animalhealthaustralia.com.au Accessed April 2023
  3. NSW DPI Strategic Plan 2022-2030 www.dpi.nsw.gov.au Accessed April 2023
  4. NSW LLS State Strategic Plan 2020-2030 www.lls.nsw.gov.au Accessed April 2023
  5. Australia DAFF www.agriculture.gov.au Accessed April 2023
  6. Paraboss www.paraboss.com.au Accessed April 2023
  7. MLA From idea to impact - commercialisation opportunities www.mla.com.au Accessed April 2023
  8. AWI Flystrike Extension Program www.wool.com Accessed April 2023
  9. MLA, Shepherd R, Webb Ware J et al. Priority list of endemic diseases for the red meat industry - 2022 update. Published 30 June 2022 www.mla.com.au
  10. NSW DPI Primefact. Buffalo flies and their control. www.dpi.nsw.gov.au Accessed April 2023
  11. NSW DPI Primefact. Nodule worm of sheep. www.dpi.nsw.gov.au Accessed April 2023
  12. Poe I (2023) Theileria orientalis on the North Coast. Posted on Flock and Herd January 2023 www.flockandherd.net.au
  13. McKenzie RA (2002) Irritant diterpenoids of Pimelea spp. - simplexin (& huratoxin) in Toxicology for Australian Veterinarians pp 205-210 (Ross A McKenzie)
  14. St George TD, Baldock C et al. The history of bluetongue, Akabane and ephemeral fever viruses and their vectors in Australia. AHA 2001. P74 espace.library.uq.edu.au
  15. NSW DPI Policy - Biosecurity - Endemic diseases of animals www.dpi.nsw.gov.au Accessed April 2023
  16. NSW DPI Procedure - Biosecurity - Managing significant endemic diseases of animals www.dpi.nsw.gov.au Accessed April 2023
  17. Analysis of LHMS data by Power BI. Accessed April 2023

 


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