Katie Hennessy

Eastern Equine Encephalitis Cases High This Year

As of November 3, 2021, the state of Florida has had 18 confirmed cases of Eastern Equine Encephalitis (EEE). We discussed this topic back in January, but due to the high case numbers this year, it is worth revisiting the topic. Usually rare, 2021 has had a relatively large number of equine cases which is concerning as this disease is often fatal. Most of the affected horses this year were either under-vaccinated or hadn’t received any vaccine against EEE. 


The virus that causes EEE is transmitted via mosquito bites. All of the cases this year presented to the veterinarian with neurological signs such as depression, difficulty walking, muscle twitches, recumbency or inability to stand. More than 90% of horses with EEE die within just three days of showing signs and those that survive are left with permanent neurological issues that may be severe enough to warrant euthanasia. 


If vaccinated with the complete protocol followed by the recommended boosters, your horse has less than 0.2% risk of developing this nasty disease. Appropriately vaccinated horses are also less likely to develop a severe illness than unvaccinated/under-vaccinated animals. In adult horses that have been vaccinated regularly, twice a year is appropriate. For unvaccinated adult horses, they should have 2 doses 3-4 weeks apart and then twice a year after. Foals should be vaccinated between 4-6 months with 2 doses, 4 weeks apart and then boostered at 10-12 months of age. 


For more information speak with your veterinarian or check out the AAEP and EDCC factsheets. Suspected and confirmed cases of EEE must be reported to the State Veterinarian’s Office, if you have any concerns about your horse please contact your veterinarian immediately. 

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