It’s a good idea to consider vaccinating horses against Eastern Equine Encephalitis (EEE). The wet weather is increasing mosquito populations that vector this disease to humans and horses.  There have been cases of EEE in horses this year.  We see cases every year despite vaccinations being very effective.

This disease cycle is interesting.  The virus circulates in bird populations near swampy areas.  Mosquitoes spread it between birds.  Then mosquitoes that feed on both birds and other hosts can vector this disease outside the normal cycle.  Humans and horses are commonly infected but are terminal hosts.  This means mosquitoes biting humans or horses can’t become infested with the virus and move it to other animals.  Birds are the reservoir of this virus.

I personally had a horse contract EEE.  This was due to a vaccine handling error on my part.  I placed the vaccines in my back pocket on a warm day to carry the vaccines to the horses.  She was the last horse vaccinated that day.  The heat decreased the efficacy of the vaccine.  I now carry vaccines in a small cooler with an ice pack while vaccinating horses in my barn.  The mortality rate in horses is 90% for this disease.  I was blessed that my girl survived with very little lasting issues.

Since mosquitoes are the vector of this virus, controlling this disease in horses is two-fold.  First, vaccinate against it.  UF Large Animal Hospital’s, Dr. Sally DeNotta, recommends vaccinating Florida horses 2 to 3 times per year with one vaccination being in the spring.  Horses that have never been vaccinated or have an unknown vaccination history, should be vaccinated then receive a booster 4-6 weeks later to elicit the appropriate immune response.

The next step to controlling EEE is mosquito management.

• Empty containers around the yard and barn that hold water after rain.
• Use a mosquito larvicide such as Bti dunks in water troughs.  Read the label and choose one that is safe for livestock drinking water.
• Clean water troughs weekly.  If you see wiggly larvae in your water troughs, you are breeding mosquitoes.  Dump it out!
• Insect repellent for you and your horses is a good idea, especially during low light hours.

We see an increase in mosquitoes following rain events like tropical storms and hurricanes.  This leads to cases of EEE in horses.  Protect your horses by vaccinating and controlling mosquitoes.  For more tips on mosquito management, we have this EDIS publication.  For more information on vaccination in Florida, we have this EDIS publication.

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