PORTSMOUTH — The state Department of Environmental Management has determined that a horse that died over the weekend was a victim of rabies. Portsmouth police report that the horse was located at the Newport Polo Club Office and Arena at 2503 East Main Road.

A call to the club was not returned.

Scott Marshall, DEM veterinarian, said they were notified of a female horse "acting aggressively" on Saturday night. The horse's regular vet attempted to treat it Sunday afternoon, Mr. Marshall said, but could not get close enough as the horse would "reportedly charge if you get near it."

DEM planned to go out and sedate the horse for testing but it died Sunday night. The horse's vet removed its head for testing and the body was buried. DEM concluded from testing on Tuesday morning that the horse had died from rabies.

The virus is usually transmitted through a bite, traveling through the nervous system from the bite origin until it reaches the brain. It is produced in the salivary glands where it can infect other mammals. Rabies can be difficult to detect because it mimics other diseases, Mr. Marshall said, and the incubation period varies greatly from animal to animal. Once it infects the brain, it will kill the animal within days.

"If (the horse) is bitten at the tip of the tail, it has a longer incubation period," he said. "But if the horse is bitten on the nose, it reaches the brain faster."

Mr. Marshall said the horse must have been bitten by a rabid animal to have contracted the virus but the club's operator reported no finding of any "wound of unknown origin or of (the horse) coming into contact with another animal."

The horse's vet reported to Mr. Marshall that its rabies vaccination had lapsed. Mr. Marshall said vaccinations are required for publicly-shown horses but not for privately-owned horses.

The dead horse shared a paddock with another horse, Mr. Marshall said, adding that DEM is working to determine whether any other animals in the club were infected but he has not been able to reach anyone at the club.

The Department of Health is looking into whether there was any contact with humans in which the virus could have been transmitted.

The federal Center for Disease Control reports that less than 10 percent of reported rabies cases occur in domestic animals.

BY JILL RODRIGUES

jrodrigues@eastbaynewspapers.com