Vaccination Protects Horses from Deadly Mosquito-Transmitted Viruses

– The Department of Agriculture, Trade and Consumer Protection (DATCP) is encouraging horse owners to vaccinate their horses to protect the animals from mosquitos carrying the deadly West Nile Virus (WNV) and Eastern Equine Encephalitis (EEE). Last year, Wisconsin had a record 24 confirmed cases of each virus.

“It’s very sad to see horses affected by these viruses when vaccination can usually prevent illness. (EEE) is fatal in approximately 90% of clinical cases and (WNV) is fatal in approximately 30% of clinical cases,” said Dr. Julie McGwin, DATCP equine program veterinarian. According to the Equine Disease Communication Center, the number of cases of EEE reported by southern states has increased more this year than the same time last year.

WNV and EEE may cause encephalitis, or inflammation of the brain. Symptoms of encephalitis in horses include depression, appetite loss, drooping eyelids and lower lip, fever, weakness, twitching, paralysis or lack of coordination, aimless wandering, circling, and blindness. Horses may also go down, be unable to rise, exhibit seizures, or become unresponsive, especially with EEE, which can be fatal within 24 hours.

Horses that have never been vaccinated will need two doses of the vaccination initially, and then boosters at least annually. It takes at least two weeks to build up enough antibodies to protect the horse and the vaccine will not protect the horse if given after the horse is infected. Horse owners should check with their veterinarian to ensure their horse’s vaccines are current.  

Besides vaccination, other steps to limit a horse’s exposure to mosquitoes during warm weather include:

  • Remove items from surrounding property that could collect stagnant water such as old tires, tin cans, plastic containers.
  • Keep rain gutters clean and draining properly.
  • Clean and chlorinate swimming pools, outdoor saunas and hot tubs, and drain water from pool covers.
  • Turn wading pools and wheelbarrows upside down when not in use.
  • Empty and replace water in birdbaths at least once a week.
  • Consider keeping horses in the barn from dusk to dawn, when mosquitoes are most active.
  • Discuss using equine mosquito repellents with your veterinarian.

The virus is not contagious between horses. While humans may also be infected by WNV and EEE, the viruses do not pass directly between people and horses. Mosquitoes carry the viruses from infected birds and the only route of transmission is from a mosquito bite.

Because the viruses follow mosquito populations, the threat varies depending on the weather but normally starts in mid- to late summer and remains until the first killing frost. For more information about EEE and WNV and other horse diseases, visit DATCP’s website at https://datcp.wi.gov/Pages/Programs_Services/AnimalDiseases.aspx.



Robert graduated from Brandman University, where he got his bachelor’s degree in Business Administration. Born in Massachusetts, Robert’s family moved to Kentucky in 2005 where he spent his college life and worked as an insurance agent for four years. Now is the founder and team leader of the website.


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