With the mosquito season approaching, officials from the Massachusetts Department of Agricultural Resources (DAR) are advising horse owners to take preventative measures to protect animals against mosquito-borne diseases like West Nile virus (WNV) and Eastern equine encephalitis (EEE).

Annual vaccinations should be administered during the spring to ensure animals are protected prior to the peak arboviral season beginning in late July and August (in Massachusetts). Owners are urged not to wait until positive cases are reported in their area, since it can take several weeks for an animal to be fully protected by a vaccine.

"It is important to stay a step ahead of these diseases and administering vaccinations in a timely manner is the best way to protect our equine population," said DAR Commissioner Greg Watson.

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