WNV, EEE Identified in Massachusetts Horses

According to the Massachusetts Department of Agricultural Resources (MDAR), both West Nile virus (WNV) and Eastern equine encephalitis (EEE) have been identified in resident horses.

A horse in Ludlow tested positive for WNV on Aug.13 and has since been euthanized due to complications from the disease. On Aug. 23, a horse from Georgetown was confirmed positive for EEE and has since died from complications associated with the disease.

In horses, clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations (twitching); 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%.

Mosquitoes carry the disease from birds to horses. A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. Its fatality rate 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. Sixty equine EEE cases were confirmed in the United States in 2011, according to USDA Animal and Plant Health Inspection Service equine disease surveillance.

Animal owners are reminded that there are USDA licensed vaccines available to protect horses from WNV and EEE. In addition to vaccination, owners should reduce potential mosquito breeding sites on their property by eliminating standing water from containers such as buckets, tires, and wading pools, especially after heavy rains.

Horse owners should consider keeping horses in indoor stalls during times of peak mosquito activity between dusk and dawn to reduce their risk of exposure to mosquitoes. Use of approved mosquito repellents is also recommended.

If an animal is suspected of having WNV or EEE, owners should contact their veterinarian immediately. The presence of these diseases must be reported to MDAR's Division of Animal Health by calling 617/626-1795 and the Department of Public Health by calling 617/983-6800.

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