Equine Flu Transmission Examined in Report

Public health authorities are looking into how equine influenza spread among 5,000 horses during an outbreak in Australia in 2007. Although the team identified a few possible methods for spreading the virus, including spread by birds and other animals, they reported in a recent review that they were unable to prove whether these potential transmission scenarios occurred.

"The virus is thought to be transmitted through direct contact with infected horses and contaminated equipment or indirectly from contact with droplets generated when the animals coughed or sneezed over a short distance," said Paula J. Spokes of the New South Wales Department of Public Health Officer Training Program. But in some instances during this outbreak, horses became infected without a clear mode of transmission.

"The speculation that birds might have served as carriers strikes me as plausible," said Tom Chambers, PhD, head of the OIE Reference Laboratory for Equine Influenza at the University of Kentucky's Gluck Equine Research Center, who commented on the report. "However, none of the Australian horses were vaccinated. In the USA, effective vaccines are available. If a horse is vaccinated using vaccines containing appropriately protective virus antigens, then we can hope and expect that transmission by birds would be unimportant, even if biologically possible."

The team also investigated the possibility of windborne spread of the virus.

"It was suggested that windborne spread of the virus had occurred in some areas over long distances," Spokes said. "Long distance windborne spread of infection has not been reported for human influenza virus transmission, so it was important to understand how the virus was spread in these conditions."

They showed the virus was unlikely to have been spread by the wind, which Chamber said was good news. "Whether flu has the ability to be transported downwind over long distances (greater than 40 yards) and still cause infections is a question that I and others have raised from time to time with no good evidence to answer it," Chambers noted. "So it comes as a bit of relief to see that these unexplained transmissions are not associated with wind direction."

Regardless, good infection control is imperative during a disease outbreak. "Restricting the movement of horses and horse associated equipment is important," Spokes noted. "Ensuring that humans that have been working with horses do not spread the disease to other properties is also important."

The study, "Investigation of equine influenza transmission in NSW: Walk, wind or wing?" was published in the September/October NSW Public Health Bulletin. The abstract is available on PubMed.

About the Author

Marie Rosenthal, MS

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