Canine flu: How big a threat?

Clinicians grapple with immunization policy

Published: November 17, 2009
By Edie Lau

Had the new canine influenza vaccine come out in ordinary times, veterinarians may have had little trouble deciding whether, when and to which owners’ dogs to offer the shot. Clients might easily have grasped that the shot is appropriate for dogs that congregate in places such as boarding kennels and shows, but not necessary for stay-at-home pets.

But times are not ordinary.

With a human pandemic flu in full swing and fresh evidence that the virus in people has passed to pet ferrets and a house cat, flu viruses of all varieties are stoking high anxiety. That’s translated into unusual — some say unwarranted — public interest in the dog flu shot and a heightened sensitivity among clinicians on the subject.

This question, posted on a Veterinary Information Network (VIN) online discussion board by Dr. Steven Barta in Michigan last month, exemplifies the concern: “How do you tell clients that you have the vaccine without causing panic?”

Dr. Cynda Crawford, the University of Florida veterinary researcher who discovered the canine influenza virus in 2004, agreed that practitioners must be careful how they speak, because the term “flu” has become “a dirty word.”

“I think myself and my colleagues have to be very careful with our words right now because the climate is so hot and we can’t control how people react,” Crawford told the VIN News Service.

Crawford, an expert in immunology and infectious disease, said off-hand diagnoses of the flu based purely on clinical signs can have devastating consequences. In one case in South Carolina, a dog adopted from a shelter was returned and ultimately euthanized after the owner was told by a veterinarian that the dog had the flu, although the animal had not been tested, Crawford said.

At the same time, the flu is a real risk in shelters, kennels and anywhere else that dogs are gathered in numbers. “Every Thanksgiving since 2004, we’ve had a canine-flu outbreak somewhere in a boarding situation,” Crawford said.

Canine influenza is a disease of dogs; no evidence exists that people can catch it. Like human flu patients, dogs with canine influenza develop respiratory symptoms such as coughing and sometimes runny noses. And like humans, most dogs that contract the flu will be only mildly sick and recover on their own. In a small percentage of cases, flu infection will lead to secondary bacterial infections that can cause more serious, even life-threatening, illness.

The risk is driving many boarding kennels to require the canine influenza vaccine as a condition of boarding. The immunization, made by Intervet/Schering-Plough Animal Health, was granted a conditional license by the U.S. Department of Agriculture’s Animal Health Inspection Service (USDA APHIS) in June.

According to a USDA news release, the agency “issues conditional licenses in the event of an emergency situation, limited market or other special circumstance. In this case, the special circumstance was the emergence of a new virus for which there were no existing licensed veterinary vaccines.”

During the conditional license period of one year, APHIS’s Center for Veterinary Biologics will continue monitoring the product’s performance and evaluate the company’s progress toward full licensure.

Before granting the conditional license, the agency accepted data supporting product purity, safety and “a reasonable expectation of efficacy.” Studies, including field safety trials, had indicated that the vaccine can reduce the incidence and severity of lung lesions and shorten the duration of coughing and viral shedding, the release said.

Immunization requires two shots given over a two- to four-week period.

The canine influenza vaccine is not a “core” vaccine, but rather a “lifestyle” immunization, to be used only under certain conditions. Since its release, practitioners have been puzzling over just what conditions warrant it. For instance, they wonder, is it appropriate for a boarding kennel to require the shot in a region where canine influenza is not known to be circulating?

Dr. Stephanie Ensley in Arkansas saw how easily rumor and anticipation can run riot last week when she caught a local television news story in which a veterinarian spoke of an impending outbreak and reported that her own clinic’s kennel had to be shut down for cleaning following illness among boarders.

Ensley posted on VIN that she called the clinic owner to ask where the confirmatory tests were sent. “I was told that they were actually severe cases of Bordetella, but that there was an outbreak two weeks ago in a city about 200 miles away, and they are preparing for the ‘inevitable,’ ” she related.

Ensley then called critical care and general practice facilities in that city. Her sleuthing turned up a big nothing: “I ... was told they were not aware of any cases and had not felt the need to test any animals,” she said. “The diagnostic lab has no positive cases from this area ...”

Meanwhile, the news report raised concerns among dog owners, predictably. “Now clients are calling with questions,” Ensley said. “Clients who do not even have pets on heartworm prevention want this vaccine.”

In Virginia, Dr. Ebalinna Vaughn told colleagues on VIN about a puppy being treated for presumed canine influenza that — while awaiting laboratory test results — was given the vaccine, as well. “This just seems like overkill to me,” she said.

“I just hate the fact that I’ve been forced to get this vaccine because several of my clients were told by their boarding kennel that their dogs are required to have this vaccine before boarding,” Vaughn added, echoing sentiments posted by other practitioners. “I did have one client decide to find a pet sitter instead of giving the vaccine after we talked about it.”

Crawford said she understands both veterinarian and kennel-owner perspectives on the issue. “As a veterinarian, I would prefer that policies like that be made on evidence,” she said. “At the same time, I have seen a few boarding establishments here in Florida just wiped off the face of the Earth financially (after an influenza outbreak).”

Like boarding establishments, clinics may have an interest in playing it safe, Crawford added. “Now (that) there’s a vaccine, what is your liability if you don’t tell clients about it?” she said. “If I do not tell clients whose dogs are socially active in the community, and they go out and get canine flu, they may come back and say, ‘Why didn’t you tell me there was a vaccine?’ ”

Barta, the Michigan practitioner wondering how to broadcast the availability of the vaccine without inciting panic, ended up preparing a short letter for clients on the subject. It reads in part:

“This vaccine does not prevent the disease but it lessens the severity of the disease. After careful consideration and research we feel that this is an important vaccine to be given to any dogs that fall into the following categories:

  • Kenneled dogs or those that visit doggie day care
  • Frequent visits to the groomer
  • Dogs that play at dog parks
  • Out-of-state travelers
“In essence, dogs that receive the Bordetella vaccine are also candidates for the Canine Influenza Vaccine.”

The letter apparently met his goal of being informative without causing a panic. Two and a half weeks after he sent it out, Barta said the demand was “surprisingly low.”

Canine influenza originally was discovered among racing greyhounds in Florida in 2004. Before that, dogs were not known to be susceptible to the flu. The flu subtype, H3N8, evolved from a virus that infects horses.

Crawford said the virus has since reached 29 states and the District of Columbia, with urban areas in Colorado, New Jersey, New York, Pennsylvania and Florida particularly hit hard.

Comprehensive information about the distribution of canine influenza isn’t available because no single organization tracks it; despite the public-health ramifications of the virus, influenza is not a reportable disease for human or veterinary patients.

From what she has heard, Crawford said the canine virus continues to spread. “We have had active cases this summer and new areas in New Jersey and Delaware. We have new cases or outbreaks in Northern Virginia, around the greater Atlanta area and (in) Georgia. This is just since July,” she said.

Crawford said the main laboratories that offer canine influenza analysis are at Colorado State University, Cornell University and the University of Florida. She said Idexx also has a good test.

Edward Dubovi, director of the virology laboratory at Cornell’s College of Veterinary Medicine Animal Health Diagnostic Center, where the canine influenza virus was first isolated, said the lab receives 40 to 50 samples a week for serology screening and another 10 to 20 samples per week for PCR, or genetic, testing.

The numbers of samples received involving a variety of species is up since news broke this month that human pandemic flu, H1N1, had been diagnosed in a pet cat. Dubovi said the lab last week received about 10 samples total from cats and ferrets, plus one from a pig. Cats, ferrets, pigs and turkeys have all been found to be susceptible to pandemic H1N1.

Many researchers think dogs are likely to be found with H1N1 infections as well, given the virus’ worldwide prevalence. (According to the World Health Organization, more than 206 countries and territories or communities had reported laboratory-confirmed cases of pandemic influenza H1N1, including more than 6,250 deaths, as of Nov. 8, the latest date for which information is available.)

With potentially two different flu bugs able to infect dogs, is it important to identify which bug is at play? Dubovi said that’s more of an academic issue than an urgent public-health issue. “Being in an academic environment, I’m certainly willing to answer the question,” he said.

The reality is that laboratories around the world are likely to be probing the question avidly. “People are looking, I guarantee you," Dubovi said. "The world surveillance system is so finely tuned right now that it’s hard for an animal to sneeze without someone running a flu test on it.”

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