Possible Cause of Unusual Neurologic Signs in Australian Horses Identified

Australian authorities might have identified the cause of unusual neurologic signs in horses in New South Wales, Victoria, and South Australia, according to a report from the New Zealand-based website Horsetalk.

Horsetalk indicated that researchers have found two different types of infection in affected horses: alphavirus infection (i.e., Ross River virus) and flavivirus infections (i.e., Murray Valley encephalitis virus or Kunjin virus).

Both alphaviruses and flaviviruses are arbovirus subtypes, meaning they are spread by mosquitoes.

Biosecurity South Australia (SA) indicated that the company has been actively involved in diagnostic testing and that it has tested or is currently in the process of testing about 100 affected horses.

Because serology (blood tests) is not the ideal source for virus isolation (due to the short time the live virus actually spends circulating through the blood), the company said in a statement on their website, "Biosecurity SA is focusing its efforts and resources on severe neurological cases where it might be possible to obtain brain tissue for virus culture, should the animal die or be euthanized."

Thus far, about 15 horses have died or been euthanized as a result of the associated severe neurologic signs.

In an interview with an Australian ABC affiliate, Rob Rahaley, BVSc, MVSc, PhD, Dipl. ACVP, chief biosecurity officer at Biosecurity SA, said, "There's been an increase of mosquito activity (this year) but why the virus appears to be more severe, at this stage, we're not sure, and there's a quite a bit of work going on to try and isolate the viruses and sequence them to see if there's been a bit of change in the virus in its genotype."

Veterinarians recommend using fly protection products (fly sheets, fly spray, etc) on horses in these areas. It is also advisable to try to keep horses inside during dawn and dusk (peak mosquito times) to help reduce their exposure to mosquitoes.

If a horse is exhibiting neurologic clinical signs the owner should consult a veterinarian immediately.

About the Author

Erica Larson, News Editor

Erica Larson, News Editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in three-day eventing with her OTTB, Dorado, and enjoys photography in her spare time.

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