Horses
Cases of WN virus disease in horses have been documented, either by virus isolation or by detection of WN virus-neutralizing antibodies in 1999, 2000, and 2001. Approximately 40% of equine WN virus cases results in the death of the horse. Horses most likely become infected with WN virus in the same way humans become infected, by the bite of infectious mosquitoes.
In locations where WN virus is circulating, horses should be protected from mosquito bites as much as possible. Horses vaccinated against eastern equine encephalitis (EEE), western equine encephalitis (WEE), and Venezuelan equine encephalitis (VEE) are NOT protected against WN virus infection. A West Nile virus vaccine for horses was recently licensed, but its effectiveness is unknown. Horses infected by WN virus develop a brief low-level viremia that is rarely, if ever, infectious to mosquitoes. There is no reason to destroy a horse just because it has been infected with WN virus. Data suggest that most horses recover from the infection. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.
- Owners should eliminate standing pools of water where bugs can breed and keep their animals stabled inside during the morning and evening when mosquitoes are more likely to be feeding.
- Clean water troughs weekly and eliminate stagnant water in puddles, buckets and tires.
- Screen windows, turn off lights at night, or use fluorescent lights, which do not attract mosquitoes.
Clinical symptoms seen in infected horses include:
- elevated temperature
- stumbling, lack of coordination
- weakness of the limbs or partial paralysis.
Of unvaccinated horses that exhibit clinical signs from the infection, one in three will most likely die from the infection. The symptoms of West Nile virus are similar to Western Equine Encephalitis, which owners typically vaccinate their horses against.
Although both humans and animals have died from the disease, most West Nile virus infections do not cause any illness in either humans or animals. Horses do not transmit the virus to humans or other animals.
The CDC states that there is no reason to destroy a horse just because it has been infected with West Nile virus. Data suggest that most horses recover from the infection. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.