Two horses residing near Groveland in Lake County, Fla., have died after contracting Eastern equine encephalitis (EEE), according to a Dec. 9 press release from the Lake County Health Department. Neither horse had been vaccinated for the disease, the press release said.

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. The fatality rate for EEE in horses is 75-95%. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care. Horses that survive might have long-lasting impairments and neurologic problems.

Clinical signs of EEE include moderate to high fever, depression, lack of appetite, cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (aggression, self-mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs, such as head-pressing, circling, blindness, and seizures.

According to the USDA Animal and Plant Health Inspection Service National Animal Health Surveillance System (NAHSS), 92 cases of EEE were confirmed in Florida in 2010, including six in Lake County. Only three cases had been reported statewide as of Oct. 24, which marks the latest tracking update from the NAHSS