West Nile virus causes serious neurological disease in horses with no treatment. Vaccination is highly effective at preventing this potentially fatal condition in regions where the virus is established.
WNV neurological disease causes significant suffering through progressive loss of muscle coordination, weakness that leads to inability to rise, and the distress of loss of normal function. Horses that develop severe WNV encephalomyelitis and become recumbent require intensive nursing care and face serious secondary injuries. The welfare trajectory for severely affected horses is often poor, with many requiring euthanasia. The welfare case for vaccination is compelling: WNV vaccination is among the most effective preventive measures available in equine medicine, the disease it prevents causes significant suffering, and the cost of vaccination is minimal compared to the cost of managing WNV-affected horses or the welfare cost of premature death. In endemic regions, WNV vaccination should be considered as essential as tetanus vaccination.