Maine state veterinary officials are reminding owners that now is the time vaccinate horses to help protect them from rabies and mosquito-borne diseases such as Eastern equine encephalitis (EEE) and West Nile virus (WNV).
Vaccinating horses annually against rabies, EEE, and WNV is one of the most important ways to protect them from these dangerous diseases, which can cause neurologic signs and lead to death, especially in unvaccinated animals. Maine Department of Agriculture, Conservation, and Forestry officials are cautioning against complacency; even though there were no cases of rabies, EEE, or WNV in Maine horses last year, annual vaccination is safe, effective, and essential to maintain protection against these potentially deadly infections, they say.
Rabies—a zoonotic disease that can be spread from animals to humans—is caused by a lyssavirus that affects the neurologic system and salivary glands. Horses are exposed most commonly through the bite of another rabid animal.
In horses rabies’ clinical signs are variable and can take up to 12 weeks to appear after the initial infection. Although affected horses are sometimes asymptomatic, an infected horse can show behavioral changes such as drowsiness, depression, fear, or aggression. Once clinical signs appear, there are no treatment options.
Rabies can only be diagnosed postmortem by submitting the horse’s head to a local public health laboratory to identify the rabies virus using a test called fluorescence antibody. Thus, ruling out all other potential diseases first is very important in these cases to avoid potentially unnecessary euthanasia.
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. 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 for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations; hyperesthesia (hypersensitivity to touch and sound); changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional somnolence (drowsiness); propulsive walking (driving or pushing forward, often without control); and "spinal" signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia. Equine mortality rate can be as high as 30-40%.
Horse owners can also minimize the chances of their horses interacting with the wildlife species that commonly transmit the rabies virus by cleaning up potential food sources for these animals such as trash, grain, and food left out for barn cats.
In addition to vaccinations, horse owners also need to reduce the mosquito populations and their possible breeding areas. Recommendations include removing stagnant water sources, keeping animals inside during the bugs’ feeding times, which are typically early in the morning and evening, and using mosquito repellents.
Owners whose horses are showing signs of these diseases are urged to contact their veterinarian immediately. Suspicion of rabies, EEE, or WNV infection in horses should be reported to the Maine State Veterinarian’s office immediately at 207/287-7615.