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Australian veterinary journal2024; 102(7); 342-352; doi: 10.1111/avj.13331

Horse populations are severely underestimated in a region at risk of Hendra virus spillover.

Abstract: To identify the size and distribution of the horse population in the Northern Rivers Region of NSW, including changes from 2007 to 2021, to better understand populations at risk of Hendra virus transmission. Methods: Census data from the 2007 Equine Influenza (EI) outbreak were compared with data collected annually by New South Wales Local Land Services (LLS) (2011-2021), and with field observations via road line transects (2021). Results: The horse populations reported to LLS in 2011 (3000 horses; 0.77 horses/km) was 145% larger than that reported during the EI outbreak in 2007 (1225 horses; 0.32 horses/km). This was inconsistent with the 6% increase in horses recorded from 2011 to 2020 within the longitudinal LLS dataset. Linear modelling suggested the true horse population of this region in 2007 was at least double that reported at the time. Distance sampling in 2021 estimated the region's population at 10,185 horses (3.89 per km; 95% CI = 4854-21,372). Field sampling and modelling identified higher horse densities in rural cropland, with the percentage of conservation land, modified grazing, and rural residential land identified as the best predictors of horse densities. Conclusions: Data from the 2007 EI outbreak no longer correlates to the current horse population in size or distribution and was likely not a true representation at the time. Current LLS data also likely underestimates horse populations. Ongoing efforts to further quantify and map horse populations in Australia are important for estimating and managing the risk of equine zoonoses.
© 2024 The Authors. Australian Veterinary Journal published by John Wiley & Sons Australia, Ltd on behalf of Australian Veterinary Association.
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Publication Date: 2024-04-03 PubMed ID: 38567676DOI: 10.1111/avj.13331Google Scholar: Lookup
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Summary

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Horse populations in the Northern Rivers Region of New South Wales are much larger than previously reported, indicating that risk assessments for Hendra virus spillover may have underestimated the true threat.

Research Purpose and Importance

  • Objective: To identify the size and distribution of horse populations in the Northern Rivers Region of NSW from 2007 to 2021.
  • Why it matters: Accurate estimates are crucial for understanding risk areas for Hendra virus transmission from horses to humans and other animals.

Data Sources and Methodology

  • Three main data sources were analyzed:
    • 2007 Equine Influenza (EI) outbreak census data
    • Annual horse population data (2011-2021) collected by New South Wales Local Land Services (LLS)
    • Field observations recorded in 2021 through road line transects using distance sampling methods
  • Comparisons were made between these datasets to detect changes in population size and distribution over time.
  • Linear modeling was used to estimate the likely true horse population in 2007 based on observed trends.
  • Environmental predictors such as land use types were analyzed to explain variations in horse density.

Key Findings

  • Reported data disparity:
    • 2011 LLS data showed about 3,000 horses (0.77 horses/km), which is 145% higher than the 1,225 horses (0.32 horses/km) reported in 2007 during the EI outbreak.
    • This discrepancy indicates that the 2007 census likely underestimated the true horse population at that time.
  • Population growth and estimates:
    • From 2011 to 2020, LLS data showed only a modest 6% increase in horse numbers, indicating relative stability in recent years.
    • Linear modeling suggested that the actual horse population in 2007 was at least twice what was reported, implying undercounting in the EI outbreak data.
    • Distance sampling in 2021 estimated the current horse population at approximately 10,185 horses (3.89 horses/km), with statistical confidence intervals ranging from 4,854 to 21,372 horses.
  • Spatial distribution and habitat associations:
    • Horse densities were found to be higher in rural cropland areas.
    • The best predictors for horse densities included the proportions of conservation lands, modified grazing lands, and rural residential areas.

Conclusions and Implications

  • Past data from the 2007 equine influenza outbreak is no longer reliable for estimating current horse population size and distribution.
  • Even recent LLS data likely underestimates the actual horse population in the region.
  • Underestimating horse populations can lead to insufficient risk assessments for Hendra virus spillover events, which can threaten both animal and human health.
  • Continuous, refined efforts to quantify and geographically map horse populations are essential for effective management of equine zoonotic diseases in Australia.

Cite This Article

APA
Linnegar B, Kerlin DH, Eby P, Kemsley P, McCallum H, Peel AJ. (2024). Horse populations are severely underestimated in a region at risk of Hendra virus spillover. Aust Vet J, 102(7), 342-352. https://doi.org/10.1111/avj.13331

Publication

Australian veterinary journal
ISSN: 1751-0813
NlmUniqueID: 0370616
Country: England
Language: English
Volume: 102
Issue: 7
Pages: 342-352

Researcher Affiliations

Linnegar, B
  • Centre for Planetary Health and Food Security, Griffith University, Nathan, Queensland, Australia.
Kerlin, D H
  • Centre for Planetary Health and Food Security, Griffith University, Nathan, Queensland, Australia.
Eby, P
  • Centre for Planetary Health and Food Security, Griffith University, Nathan, Queensland, Australia.
  • School of Biological, Earth, and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia.
  • Centre for Large Landscape Conservation, Bozeman, Montana, USA.
Kemsley, P
  • North Coast Local Land Services, Wollongbar, New South Wales, Australia.
McCallum, H
  • Centre for Planetary Health and Food Security, Griffith University, Nathan, Queensland, Australia.
Peel, A J
  • Centre for Planetary Health and Food Security, Griffith University, Nathan, Queensland, Australia.

MeSH Terms

  • Animals
  • Horses
  • Henipavirus Infections / epidemiology
  • Henipavirus Infections / veterinary
  • New South Wales / epidemiology
  • Hendra Virus
  • Horse Diseases / epidemiology
  • Horse Diseases / virology
  • Disease Outbreaks / veterinary
  • Population Density

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