Boise, Idaho - The Idaho State Department of Agriculture (ISDA) has confirmed multiple cases of equine West Nile virus (WNV) in three horses in Canyon County. 

The three cases are unrelated to one another, and the horses reside at three separate facilities in the county. All three horses are recovering and under the treatment of a veterinarian, however none of the three horses had previously been vaccinated for WNV.   

The most common signs of WNV in horses are fever and weakness, usually in the hindquarters which sometimes is characterized by a widened stance, stumbling, leaning to one side and toe dragging. Mental conditions such as fearfulness, lip-smacking, chewing movements and fine muscle tremors may be noticed. Paralysis and inability to stand may follow in extreme cases of WNV infection.  

West Nile is most commonly spread to people and horses through the bite of an infected mosquito. The public should continue to take precautions in areas with WNV-carrying mosquitoes and precautions should extend to animals.  

The ISDA recommends two essential protections for equines and small camelids; vaccination and physical precautions.  

“The West Nile virus vaccination continues to be an essential preventive measure and should be given annually to all horses to provide an adequate level of protection from the virus,” said Idaho State Veterinarian Dr. Scott Leibsle. “Nearly 98 percent of horses that test positive for West Nile are non-vaccinated or under-vaccinated. Horse owners should speak with their veterinarians about the West Nile vaccine and other annual core vaccinations to develop an annual booster schedule. Horses that have been vaccinated for WNV in previous years must receive an annual booster; a one-time vaccination is not enough.”  

 Physical WNV precautions include using fans and repellants to keep mosquitoes away from equines. Additionally, horse owners should remove standing water on or near their property whenever possible.  

Additional information about the virus and a map of known affected counties is available from the Idaho Department of Health and Welfare.

For questions regarding control of mosquito populations, contact your local mosquito abatement district.