West Nile Virus Disease
West Nile virus (WNV) is a virus that is transmitted from migrating carrier birds to mammals through the bite of various mosquito species, particularly Culex species. Horses and humans have been known to be particularly affected by West Nile virus, which travels through the bloodstream to the brain and the spinal cord, resulting in an inflammation which can cause severe and potentially fatal neurological symptoms. Originating in Africa many years ago, the virus has spread throughout the world, and is now known to also occur in Australia, Asia, Europe, and North America. After being initially diagnosed in the United States in 1999, WNV rapidly became a nationwide epidemic which debilitated tens of thousands of horses, with a substantial mortality rate. Although this virus can only be transmitted directly by mosquitoes (not from horse to horse, nor from horses to humans) every unprotected horse is at risk, particularly during the mosquito season. WNV most recently began to re-appear in Europe in a new outbreak which started in Italy in 2008, where the disease continues to affect both horses and humans. There is no cure for West Nile virus disease, but individual horses can be protected through vaccination.