Weather's Effect on Equine Influenza Transmission Studied

Researchers from the Faculty of Veterinary Science at the University of Sydney, Australia, recently evaluated weather's effect on the transmission of equine influenza.

"We have demonstrated in non-laboratory conditions how air temperature, humidity and wind velocity influence the spread of influenza viruses. It puts us in a much better position to understand an actual outbreak of influenza in horse populations, under natural conditions," said Navneet Dhand, PhD, MACVSc, MVSc, BVSc&AH, GradCert, senior lecturer and principal investigator of the research project.

The research team analyzed data from the 2007 equine influenza outbreak in Australia in addition to data provided by the Australian Bureau of Meteorology for the same time period.

The researchers determined horses were more likely to get infected on days when relative humidity was low and less likely to get infected on days when the maximum daily air temperature was 20 to 25°C (68 to 77°F).

"The results will be invaluable in modeling the spread of influenza viruses in the unique Australian environment and landscape," said Simon Firestone, the lead author of the paper and PhD candidate at the University of Sydney's Faculty of Veterinary Science.

Additionally, the team found that horses residing on premises downwind of nearby infected premises were more likely to become infected. They also noted the risk was higher on days when wind speeds were greater than 30 kilometers per hour (about 19 miles per hour), substantiating numerous anecdotal reports of the wind-borne spread of equine influenza.

"This gives an important indication of how weather conditions can affect the spread of the equine influenza virus and therefore allow us to better predict the outcome of a future incident of the virus in Australia," said Dhand.

Australia's equine influenza outbreak occurred in 2007 following a breach in the quarantine of infected imported horses. Nearly 70,000 horses on over 9000 premises in New South Wales and Queensland were infected at a cost of over $350 million. The disease was eradicated within five months, mainly due to the fast introduction of a complete ban on horses being moved.

"By having a better idea of how the disease spreads, our findings will help animal disease authorities reduce the cost of outbreak management as well as the social impacts of the outbreak," Dhand said.

The research was conducted by a team which also included:

  • Michael Ward, BVSc (Hons 1), MSc, MPVM, PhD, FACVSc, professor and chair of veterinary public health from the University of Sydney;
  • Jenny-Ann Toribio, BVSc (Hons), PhD, MANZCVS, MEd(Higher Education), associate professor, from the University of Sydney;
  • Barbara Moloney, BVSc, MVS, MACVSc, technical specialist at the New South Wales Department of Primary Industries; and
  • Naomi Cogger, PhD, lecturer in Veterinary Epidemiology at the new Zealand's Massey University Epicentre.

It was a part of a jointly funded project supported by the Rural Industries Research and Development Corporation's Horse research program, and the Animal Biosecurity Cooperative Research Centre for Emerging Infectious Diseases.

The study, "The Influence of Meteorology on the Spread of Influenza: Survival Analysis of an Equine Influenza (A/H3N8) Outbreak," was published on April 21 on PloS One and can be viewed online.

About the Author

University of Sydney

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