EEE Hammers Florida; Veterinarians Recommend Vaccinating

Eastern equine encephalomyelitis (EEE) virus is quite active this year, and more than 120 cases have been reported in Florida. The state veterinarian's office in Tallahassee, Fla. predicts levels equal to 2003 in which there were 200 cases of EEE in horses. 

During the 2003 outbreak, most of the infected horses were not vaccinated and were younger than three years of age. Horses that were vaccinated but became ill were also vaccinated less frequently overall. Some had only primary immunizations while others had primary immunizations and only yearly boosters. Vaccination against EEE should be performed at a minimum of two times per year and three times is recommended during years of high activity.

All horses that have not been previously vaccinated for EEE should receive two initial injections one month apart. Foals should be vaccinated at four, five, and six months of age if the mares have been vaccinated previously. If there is questionable immunity in the foals, vaccination can commence as early as two to three months.

Some EEE vaccines can be obtained over the counter. If any vaccine becomes warm while transported, it can be rendered inactive after only a short period; therefore, owners run the risk of inappropriate vaccination when performing their own immunizations.

Death loss resulting for EEE infection in horses is as high as 90%, and of the remaining 10% that survive, less than 1% perform at original levels again. In the 2003 outbreak, 100 owners of EEE survivors responded to a follow-up survey performed by the University of Florida and funded by the USDA and Florida State Department of Agricultural Services (the study is not yet published, but has been presented at two public health meetings). The total value of only these 100 horses was close to $250,000 and, in total, veterinary costs came to $40,000 for EEE treatment. The cost spent on vaccination was less than $4,000 for those 100 horses in the subsequent year.

Clearly the cost of vaccination per horse is much lower than EEE monetary and emotional losses to owners.

About the Author

Maureen Long, DVM, PhD, Dipl. ACVIM

Dr. Maureen Long is Associate Professor in the Department of Infectious Diseases and Pathology at the University of Florida and teachings microbiology and immunology. Her research focus is infectious disease of horses.

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