An Alberta man who was bitten by a bat while sleeping has developed rabies, which rarely affects humans but is often deadly, an Alberta Health official said Friday.

A bat, like this one captured in Alberta in 2006, has infected an Edmonton-area man with rabies.

The man — who lives east of Edmonton — did not get treated after he was attacked in August 2006 and is now in serious condition in hospital, said Dr. Karen Grimsrud, a provincial health officer.

Rabies, which ravages the brain and spinal cord, is fatal in more than 50 per cent of human cases that are not immediately treated, according to Health Canada. The federal agency reports that 21 persons have died of rabies in Canada since 1925.

In most cases, it takes months before an infected person notices any symptoms, which can include extreme anxiety, paralysis, convulsions and difficulty swallowing.

Grimsrud said the Alberta man woke up in the middle of the night when the bat bit him, but he didn't show any symptoms until January.

'Once you develop the neurological symptoms, there's very little that can be done.' —Dr. Karen Grimsrud

"Once you develop the neurological symptoms, there's very little that can be done," Grimsrud said Friday. "All we can do is make them comfortable."

Rabies is transmitted through the bite or scratch of an infected animal but is usually passed from animal to animal, rarely affecting humans. Animals known to transmit the disease include foxes, raccoons, skunks and bats.

Alberta hasn't had a human case since 1985, when a Calgary man developed rabies after being bitten by a bat.

People who suspect they've been exposed to the virus that causes rabies are urged to seek medical attention as soon as possible.

"Any bat bite really needs a follow-up because there is always that potential that they could have rabies and, through the bite, spread the virus to the person that they bit," Grimsrud said.

Man's friends, family being checked

Since the Edmonton case was discovered, health regions in Alberta have been contacting doctors, medical staff, family members or friends who may have come in direct contact with the infected man's saliva or bodily fluids.

This is a precautionary measure, as there has never been a documented case of humans transmitting rabies to other humans.

"We're being extra cautious in this case," said Grimsrud.

Among the most recent cases, a British Columbia man succumbed to the infection after a suspected bat bite in 2003. Three years earlier, a nine-year-old Quebec boy died after he was bitten by a bat.

With files from the Canadian Press