One month after reporting the first case of Eastern equine encephalitis virus (EEEV) in a horse in Polk County, an additional horse with EEEV infection was reported the week of May 8-14 in Osceola County, according to Florida Arbovirus Surveillance.

Eastern equine encephalitis virus /CDC
Eastern equine encephalitis virus /CDC

The Equine Disease Communication Center (EDCC) offers more details: On May 13, a new EEEV case was confirmed in Osceola County, Florida. The two year old, unvaccinated Mustang had not been off the premises in over a year. Clinical signs began on May 6 and the horse was euthanized for humane reasons on May 7.

EEEV is a mosquito-transmitted disease that is much more severe than West Nile Virus (WNV).  The mortality rate in horses from WNV is reported at around 30%, while the rate for EEEV is almost 90%.  Infected mosquitoes are the primary source for EEEV.

The virus causes inflammation or swelling of the brain and spinal cord.  General symptoms include central nervous system signs such as: head pressing, convulsions, lack of response to facial stimulation, fever above 103 degrees, ataxia, paralysis, anorexia, depression and stupor.  Other symptoms may include irregular gait, teeth grinding, in-coordination, circling, and staggering.  All symptoms may not be exhibited by an infected horse.