Most American owners are aware of the increased number of West Nile virus (WNV) cases confirmed in the U.S. horse population this year. What they might not know is how the virus affects horses in other countries.

Australia and New Zealand

According to C.J. (Kate) Savage, BVSc (Hons), MS, PhD, Dipl. ACVIM, WEVA Oceanic delegate, a similar virus–Kunjin–is endemic in parts of Australia.

"(Kunjin) is antigenically and genetically similar to WNV and was reclassified as a subtype of WNV in 1999 (WNV/Kunjin)," she said.

Parts of Australia suffered a large equine WNV/Kunjin outbreak in 2011, she said, after which Frost et al. identified a new WNV strain as the cause.

"Results showed that most of the cases were caused by a new strain of WNV, which has been termed WNV(NSW2011)," Savage explained. "This is most closely related to WNV/Kunjin. However, the new strain appears to invade nervous tissue to a greater degree than the original Kunjin virus."

Neighbor New Zealand (NZ) remains WNV-free to date; however, risk of the disease spreading to the island nation is a concern. "In 2004, New Zealand scientists looked at the possibility of WNV getting into NZ and becoming endemic," Savage explained. "It was thought that vectors and hosts were present, so great awareness was necessary."


Sandro Barbacini, DVM, Italian WEVA board member, said that Italy experienced WNV outbreaks several years ago.

"The outbreaks were in Northern Italy staring from the Ferrara area, very close to the delta of the Po River&#