Eastern Equine Encephalitis and West Nile Virus:
Vaccinate or Not

August, 2010
Sonja C. Crawford, Hendry County Extension Agent II, 4-H/Livestock

With many of the cattle ranches using horses to gather their herd, vaccinating against Eastern Equine Encephalitis (EEE) and West Nile Virus (WNV) is important. EEE and WNV are both viral diseases that are spread by mosquitoes. The mosquitoes become infected when they first feed on infected wild birds and then later on horses. These viruses are not spread from horse to horse, but are carried by the biting mosquitoes. Both of these diseases are somewhat similar in the way they are transmitted and with symptoms of the disease.

EEE and WNV affect the central nervous system. Symptoms may include, but not limited to, unsteadiness, difficulty in rising after lying down, depression, listlessness, twitching, and blindness. There is no known treatment for these viruses once infected. EEE is most life threatening than WNV; however, both diseases have killed a number of horses in Florida over the years.

Most of the horses that were infected by EEE or WNV did not receive vaccination within the last six months. If you vaccinated last year, you still need to give a booster shot this year. Preventive vaccinations are available through a licensed veterinarian as well as through most livestock supply dealers. Licensed veterinarians will assure that viable vaccine is utilized and injections are properly administered. Mistakes in vaccination protocol by well-meaning horse owners can result in ineffective protection in an animal that was thought to be risk free. All too frequently, owner vaccinated horses develop apparent cases indicating that the animal was improperly vaccinated or was vaccinated with vaccine that had lost its protective properties. Properly administered vaccinations are effective for only one year, thus, booster shots are required on an annual basis. Newly vaccinated animals require a two-shot series administered 2-4 weeks apart before protection can be guaranteed. Foals should be re-vaccinated during summer to ensure protection during the first year of life. For more information, contact your local veterinarian.

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