Owners are being urged to vaccinate their horses. (CBC)

Nova Scotia appears to have its first case of a mosquito-borne virus that is almost always fatal to horses and in rare cases can kill people.

A case of Eastern equine encephalitis virus has been confirmed in a horse in southwest Nova Scotia, an official with the provincial Department of Agriculture said Monday.

Rob Kerr, a department veterinarian, said the horse was put down.

"It was acting oddly, according to the owner and the veterinarian," said Kerr. "It wasn't drinking water. It had some slight tremors."

The virus cannot be spread directly from horse to horse. Mosquitoes pick up the virus by feeding on infected birds, then pass it on when they feed on the blood of horses.

"There's a slight possibility it could be picked up from the horse by mosquitoes and then spread to other animals, but that's apparently very uncommon," said Kerr.

Veterinarian Brian Manuel said he saw the infected horse before it was euthanized.

"The mortality of this disease and its sudden onset, it is terrifying to both horse owners and for veterinarians to have this, now, in our region," he said.

Manuel said the sick horse's owner thought the animal was drunk from eating apples in a nearby orchard. It was staggering at first, but soon worsened.

"This horse progressed rapidly to where it was on the ground and couldn't get up on its hind end and [was] thrashing in the front end," Manuel said.

In the end, the horse could not lift its head, he said.

Manuel said his clinic is expecting 120 doses of a vaccine to be delivered on Tuesday.

A slide showing the brain tissue sample of a horse suspected of having the Eastern equine encephalitis virus. (CBC)

Rare in humans

The virus is rare in humans and most people infected with it don't show any signs. In severe cases, it can lead to headaches, fever and chills, and even seizures and comas, according to the U.S. Centers for Disease Control and Prevention.

Signs and symptoms usually appear up to 10 days after someone is bitten by an infected mosquito.

The CDC said about six human cases of the virus are reported annually in the U.S. The State of New York has reported one death from the virus this year.

The virus is nearly always fatal to horses, the CDC said.

Kerr said as far as he knows, this is the first case of Eastern equine encephalitis in the province. Results on another possible case are pending, and he has heard of other horses in the area showing signs of the virus.

Kerr has alerted his counterparts in New Brunswick and Prince Edward Island.

"We want to get the word out to veterinarians so that if they see anything suspicious they can contact their veterinarian laboratories and we can determine whether this is a very limited area involved or whether it's more widespread than that," he said.

Kerr said one way to fight the virus is to try to control the mosquito population. He said bug repellent, blankets or fly hoods could be used to keep the insects away from horses.