West Nile virus (WNV) remains a threat to horses. However, with the right vaccine and preventive measures, it’s not too late for horse owners to help protect their horses against this life-threatening disease.

West Nile encephalomyelitis is an inflammation of the central nervous system that is caused by an infection with WNV. It is transmitted by mosquitoes–which feed on infected birds or other animals–to horses, humans, and other mammals. As of Sept. 3, 33 states have reported 186 cases of WNV in horses, with Louisiana and Texas having the most confirmed cases–26 and 16, respectively.

The number of reported WNV cases fell from 1,069 in 2006 to 146 in 2010, and the decline is said by health experts to reflect both vaccination and naturally acquired immunity.

"It is a good sign that the number of cases has declined over the last decade; however, there has been an increasing number of both human and equine cases, especially over the last couple months," said Tom Lenz, DVM, MS, senior director of equine technical services for Pfizer Animal Health