Equine West Nile virus cases have been reported in two Colorado counties by the State Veterinarian’s Office on Sept. 10. A 2-year-old Quarter Horse mare in Pueblo County tested positive for WNV on Sept. 9 after showing signs of ataxia, anorexia, and abnormal mentation starting on Sept. 2.
In Montrose County, an unvaccinated 4-year-old Quarter Horse gelding on a private farm also tested positive for WNV. The horse displayed symptoms such as weakness, ataxia, teeth grinding, and muscle twitching. Both horses are currently affected but alive.
EDCC Health Watch is a marketing program by the Equine Network that uses information from the Equine Disease Communication Center (EDCC) to create and distribute verified equine disease reports. The EDCC is an independent nonprofit organization funded by industry donations to provide accessible infectious disease information.
WNV 101
West Nile virus is transmitted to horses through mosquito bites. While not all infected horses show symptoms, those that do may exhibit:
- Flulike signs such as mild anorexia and depression;
- Involuntary twitching of fine and coarse muscles and skin;
- Hypersensitivity to touch and sound;
- Changes in mental activity, giving the impression of daydreaming or disorientation;
- Intermittent drowsiness;
- Propulsive walking without control;
- Spinal signs like asymmetrical weakness; and
- Asymmetrical or symmetrical ataxia.
There is no cure for West Nile virus in horses, but some can recover with supportive care. Mortality rates in equines can range from 30-40%.
Research has shown that vaccines are effective in preventing WNV. Horses previously vaccinated need an annual booster shot, while veterinarians may recommend two boosters annually in areas with prolonged mosquito seasons. Unvaccinated horses require a two-shot vaccination series within three to six weeks. It takes several weeks for horses to develop immunity after vaccination.
In addition to vaccination, owners should reduce mosquito populations and limit exposure by:
- Eliminating stagnant water sources;
- Regularly cleaning and refilling water buckets and troughs;
- Keeping horses indoors during peak mosquito activity times;
- Using approved mosquito repellents for horses.