Mosquitoes that feed on EEE-infected birds can transmit the virus to humans, horses, and other birds. | Photo: iStock

Both La Fargeville horses, an 11-year-old grade mare and a 2-year-old grade colt, were unvaccinated. They began experiencing clinical signs on July 25 and were euthanized due to poor quality of life as a result of ataxia (loss of control of bodily movements), depression, and recumbency (down and unable to rise). The colt also experienced seizures and photophobia (light sensitivity). Veterinarians submitted brain samples from the animals to the Wadsworth Center laboratory, which confirmed EEE in both. Tests for rabies and West Nile virus (WNV) were negative. The veterinarian noted that similar signs were detected last year but the owner declined to have the horses tested. Neither horse had any history of travel off the farm.

The horse in Evans Mill, an unvaccinated 6-year-old Standardbred mare, began experiencing clinical signs on July 26 and was euthanized July 28 due to poor quality of life. Signs included loss of appetite, falling, head-pressing, and leaning. Brain and blood samples sent to both Cornell University and Wadsworth labs were negative for rabies and WNV, positive for EEE, and are pending for arboviruses. The horse had no recent travel off the farm.

EEE 101

Eastern equine encephalomyelitis is caused by the Eastern equine encephalitis virus, for which wild birds are a natural reservoir. Mosquitoes that feed on EEE-infected birds can transmit the virus to humans, horses, and other birds. Horses do not develop high enough levels of these viruses in their blood to be contagious to other animals or humans. Because of the high mortality rate in horses and humans, EEE is regarded as one of the most serious mosquito-borne diseases in the United States