An outbreak of highly contagious canine influenza has swept through the shelter of the Animal Rescue League of Western Pennsylvania, resulting in the deaths of four dogs.

Another 23 dogs are sick and are undergoing treatment while shelter employees and volunteers work to keep the virus from spreading.

Because of the dog flu outbreak, the shelter in Larimer is remaining open but temporarily suspending its "open door" policy for dogs. People cannot drop off dogs there, and dogs already in the shelter can only be adopted by people who do not currently have dogs in their homes.

The shelter still is taking in dogs picked up by dog catchers for the city's Animal Control Department. Those dogs are being isolated from others in the shelter.

Also, the shelter's low-cost veterinary clinic is temporarily closed to treatment for dogs, although other animal services continue.

There is no inoculation available to prevent the disease.

"We are wearing protective gowns and have foot baths filled with disinfectant throughout the shelter," said Daniel Musher, development director for the Animal Rescue League.

The dog flu cannot be spread to people or to cats, rabbits, horses or any other types of animal.

Employees and volunteers are washing their hands before and after they handle any dog. Extra care is being used to disinfect with bleach, which kills the virus.

"The shelter will be cleaner than ever," Mr. Musher said. "We're even cleaning items such as leashes," which are used to exercise multiple dogs.

Canine influenza is airborne, which makes it very easy to transmit. People who come in contact with sick dogs, including dog feces, urine, blood and saliva, can carry the dog flu virus out onto the street or into their own homes.

Shelter workers have been advised to change their clothes in their garages or basements before coming in contact with their own dogs, Mr. Musher said.

Donna Hughes, a veterinarian who is medical director at ARL, said, "This is quite a challenge in an open-door shelter environment, but we hope the flu will run its course in two to three weeks."

The shelter has issued an emergency appeal, asking dog lovers to take a sick shelter dog or two into their homes. It could help prevent the virus from spreading throughout the shelter, and the dogs might recover more quickly in homes than in the kennel. The shelter will provide their medications.

"It would have to be homes that don't have dogs," Mr. Musher said.

There are no reports of canine influenza in any other local shelters.

Animal experts believe the disease started as an equine influenza virus that mutated to produce the canine influenza virus. About 5 percent to 8 percent of dogs that get it will die from the virus.

Two Rottweilers, a Jack Russell terrier and a mixed breed dog developed high fevers and pneumonia and had to be euthanized, Mr. Musher said.

Dogs with a mild flu will be sick for 10 to 30 days with symptoms that resemble kennel cough. There are inoculations against kennel cough, but those shots offer no protection against canine influenza.

For further information go to www.avma.org and click on public health.