Wild birds are the reservoir for the virus, which is transmitted by mosquitoes.
Limiting exposure to mosquitoes and controlling mosquitoes are fundamental in preventing the disease. The purpose of this document is to guide veterinary practitioners and field personnel in investigating and reporting suspect cases of WNV infection in equine. Nine of those horses died or had to be euthanatized. An additional 36 horses on Long Island were found to have been exposed to WNV and developed antibodies to the virus, but did not develop clinical illness. To prevent exposure of equine to WNV, it is necessary to prevent their exposure to mosquitoes.