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:

The continual spread of Buffalo Fly since they first entered NSW in 1978¹⁰;
The disappearance in the 1960s of nodule worm (Oesophagostomum columbianum) as a major endemic disease with the introduction of modern anthelmintics¹¹;
Selenium deficiency in the NSW Northern Tablelands with the introduction of pasture improvement and widespread use of superphosphate fertilisers;
The spread of Theileria strains capable of causing clinical disease from early 2000s from the mid-North Coast to most of NSW¹²;
The increase in Pimela poisonings of cattle as enterprises moved from sheep to beef in response to economic drivers¹³;
The emergence of closantel-resistant Haemonchus contortus strains in northern NSW, making the highly effective and widely used Wormkill program no longer effective; and
The patterns of transmission for Bovine Ephemeral Fever moving from sweeping epidemics in 1972, with ever increasing areas moving to cyclic epidemic waves and endemic foci¹⁴.

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 diseases^15,16 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:

Investigation of cases by District Veterinarians and private veterinary practitioners (already occurring)
Testing at NSW APHL (already occurring)
Entry of investigations into LHMS (occurring for LLS investigations)
Maintenance and enhancement of LHMS, including development of case definitions for the MLA priority diseases and ensuring accurate and complete data entry into LHMS by LLS staff (requires responsible staff)
Epidemiological analysis of LHMS data to establish state-wide and regional norms for priority endemic diseases (requires responsible staff)
Systems to ensure any anecdotal intelligence from LLS or AHPL is passed onto those responsible for analysis (requires systems for efficient information flow) or for additional regional or emerging diseases to be included for monitoring
Regular analysis for any changes in the priority endemic diseases and prompt publishing of reports (requires responsible staff)
A communications and liaison strategy (mostly utilising existing staff and systems) that ensures:

LLS, NSW APHL and private veterinary practitioners are aware of relevant trends
Results are communicated to industry extension and research bodies such as MLA, AWI and academia
Where appropriate, local livestock managers are provided with advice on risks from any changes in endemic disease incidence or severity and appropriate management steps.

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

NSW DPI Policy - Biosecurity - Management of animal biosecurity in NSW www.dpi.nsw.gov.au Accessed April 2023
Animal Health Australia, EADRA p4 www.animalhealthaustralia.com.au Accessed April 2023
NSW DPI Strategic Plan 2022-2030 www.dpi.nsw.gov.au Accessed April 2023
NSW LLS State Strategic Plan 2020-2030 www.lls.nsw.gov.au Accessed April 2023
Australia DAFF www.agriculture.gov.au Accessed April 2023
Paraboss www.paraboss.com.au Accessed April 2023
MLA From idea to impact - commercialisation opportunities www.mla.com.au Accessed April 2023
AWI Flystrike Extension Program www.wool.com Accessed April 2023
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
NSW DPI Primefact. Buffalo flies and their control. www.dpi.nsw.gov.au Accessed April 2023
NSW DPI Primefact. Nodule worm of sheep. www.dpi.nsw.gov.au Accessed April 2023
Poe I (2023) Theileria orientalis on the North Coast. Posted on Flock and Herd January 2023 www.flockandherd.net.au
McKenzie RA (2002) Irritant diterpenoids of Pimelea spp. - simplexin (& huratoxin) in Toxicology for Australian Veterinarians pp 205-210 (Ross A McKenzie)
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
NSW DPI Policy - Biosecurity - Endemic diseases of animals www.dpi.nsw.gov.au Accessed April 2023
NSW DPI Procedure - Biosecurity - Managing significant endemic diseases of animals www.dpi.nsw.gov.au Accessed April 2023
Analysis of LHMS data by Power BI. Accessed April 2023