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Veterinary Forum September 2009 (Vol 26, No 9)

Finding influenza

by Paul Basilio

    Coughing dogs are old hat in veterinary practice, but a novel pathogen raises a red flag over an otherwise innocuous sign.

    Coughing dogs are nothing new.

    You would be hard-pressed to find a veterinarian in general practice who hasn't come across the stereotypical, recently-boarded, 3-year-old Labrador retriever with an acute onset honking cough that gradually resolves over time.

    "I used to tell my students that you're not a veterinarian until you've anesthetized a dog because someone claimed there was something stuck in its throat, but it turned out to be kennel cough," jokes Elizabeth Rozanski, DVM, DACVIM, DACVECC, assistant professor in the department of clinical services at the Tufts Cummings School of Veterinary Medicine. "Kennel cough dogs tend to have a horrid cough, but they're healthy and otherwise alert."

    That's not always the case in dogs infected with canine influenza virus (CIV), a new disease that often mimics the less serious infections that typically cause kennel cough. As a result, many veterinarians are now viewing dogs that show signs of respiratory disease with an extra measure of caution.

    "Dogs with influenza are going to behave like humans with influenza," Rozanski adds. "They're going to feel a lot sicker than a dog with kennel cough or a person with a cold, and they're going to feel that way for longer." Such patients can require significantly more supportive care in order to help them recover. Some can develop pneumonia. And some of these dogs, albeit a small percentage, can even die.

    If CIV is present in a facility, such as a kennel or shelter, management can be tricky, says Lesley King, MVB, DACVIM, DACVECC, director of the intensive care unit at the Matthew J. Ryan Veterinary Hospital at the University of Pennsylvania. "It's very contagious and it is a new virus, so most of the dogs will have never seen it before and will be susceptible," she explains. "If the virus gets into a kennel or a shelter, almost 80% of the dogs are going to show signs. It's the same as if the flu got into a day care center for children."

    Understanding the risk

    Experts agree that CIV is an important emerging disease and that its elusive nature can make the disease difficult to diagnose, treat and track.

    "I don't think veterinarians know the extent of the disease yet," Rozanski says.

    Although there have been outbreaks of CIV in 30 states and the District of Columbia, it is still very much thought of as a regional disease, meaning that it's only considered a problem where there are active outbreaks. "For the practitioner, I think the best bet would be to know what is going on in his or her area," Rozanski adds. "It's important to know your community. If the practice down the road has an outbreak, that's important to know. Make friends with the boarding kennels and see what's happening in those areas. It will help to understand what's going on with your patients, which is one of the things veterinarians often struggle with. If you don't know what someone else has seen, then you have the potential to miss something that's coming into your area," she notes.

    One of the problems confronting practitioners is that fewer newly adopted puppies are local. In the past, many puppies and kittens were adopted from area shelters. However, due to the recent increase in interstate adoption, dogs are showing up in examination rooms with more unfamiliar diseases.

    "Here in New England," Rozanski says, "it is rare for us to see stray puppies. They have done such a good job with the spay and neuter programs that most of our dogs are shipped in from the south or from Puerto Rico. It's uncommon to see a mixed-breed puppy in this area because most people get their dogs from the pet store or from a breeder."

    Index of suspicion

    CIV may be hard to diagnose, but veterinarians can keep their radar elevated by staying abreast of any outbreak news and keeping an eye out for puppies brought in from out of state, as well as for those that have spent time in a kennel or in an area where CIV is prevalent.

    "If I see the mythical 3-year-old Labrador that was left at a kennel for a week and had a straightforward cough, then I would most likely have zero interest in doing other tests on that dog," Rozanski says. "By and large, those dogs are going to get better no matter what I do. The dogs I do have an interest in treating are the dogs that differ even 1% from the [kennel cough] model."

    Although some cases of CIV can be discerned from other causes of respiratory disease by the sound of the dog's cough — for example, some cases of influenza can cause a soft, moist cough as opposed to the loud, honking cough of Bordetella bronchiseptica — finding influenza poses a unique challenge.

    "In an individual dog, diagnosis can be tricky because there are two main ways to diagnose the disease," King says. "The first is to send a swab — typically from the nose or throat of the dog — for PCR analysis or virus isolation. If you test the dog between 2 and 6 days after exposure, then you're likely to be able to find the virus there."

    The problem, King explains, is that although most dogs have some clinical signs (fever, nasal discharge, cough) as early as 2 days after exposure, many owners will not bring the dog to see its veterinarian until it becomes more severely ill, or after several days when it becomes apparent that the illness will not go away on its own. "When you get out past a week after exposure, the virus is no longer replicating or shedding," King says. "You're going to get a negative result on your PCR test, but your clinical signs at that point may still be quite dramatic. It's the same as with flu in humans; people are at their most infectious before showing any symptoms."

    In a shelter environment, diagnosis is theoretically easier because if the shelter personnel are aware that CIV is a threat, PCR tests can be conducted 2 or 3 days after admission and the disease is more likely to be found. Funding for PCR tests, on the other hand, can be difficult for shelters to obtain, so the dogs often remain untested and CIV is allowed to spread.

    Antibody testing is another method of CIV diagnosis, although it can take 8 to 10 days for the titers to start to rise, which causes another timing problem.

    "If a client brought their dog in and it had been coughing for 2 weeks, you wouldn't do a PCR or virus isolation because it would be too late," King explains, "but you may do an antibody test. The problem is that often the animals present during that intermediate 'grey zone' in days 7 to 10, after the PCR results become negative and before the antibody test becomes positive."

    King adds that ideally, follow-up antibody testing should be conducted to track down a CIV diagnosis.

    Flagged for isolation

    Experts agree that in a perfect world, all coughing dogs would be isolated from other dogs for a quarantine period. This is often not feasible because of space limitations or a client's lack of awareness about the dog's infectious state. Certain measures, however, can be taken to minimize the risk of an outbreak.

    For example, obtaining a thorough history can be key, King says. "If a dog was just adopted from a shelter or purchased from a pet store and comes into the clinic a few days later with a cough, that is a huge red flag. If it's a dog that sits at home on its owner's lap and never goes anywhere, then I would be much less worried. A little bit of background is an important thing to help you say, 'Okay, this one needs to be treated as an infectious suspect.'"

    Another useful containment measure is to keep dogs suspected of having respiratory disease separate from the rest of the practice's patients. Dogs can be brought through a back door or kept in the owner's car until an examination room becomes open, King says. "Don't let potentially infectious dogs sit in the waiting room with other dogs."

    Additionally, staff should wear gowns, gloves and booties while in an examination room with a potentially infectious dog. Viruses and bacteria can be transferred to other patients via stethoscopes and other equipment, so a dedicated isolation room should have equipment that stays in that room.

    "The same protocols should be followed for possible influenza cases as would be followed for possible parvovirus cases, for example. When you leave the room you should take off the gown, gloves and booties and leave them in there. Ideally, the dogs should not be hospitalized in the practice, which is fine as long as all they have is kennel cough. The problem is that a small subset will develop pneumonia and will require hospitalization," says King.

    CIV vaccine

    In May, the United States Department of Agriculture (USDA) granted a conditional license to Intervet/Schering-Plough Animal Health for its CIV type A, subtype H3N8, vaccine. The vaccine can reduce the incidence and severity of lung lesions, as well as the duration of coughing and viral shedding, the agency said in its release.

    "The experimental research suggests that it should be quite effective at decreasing the severity of signs," says King. "It may not completely prevent disease, but it certainly seems as though it will make CIV a much less severe disease and decrease the risk of shedding. I think it definitely has utility."

    Most experts agree that this vaccine is considered noncore, which means it should be used in dog populations where veterinarians are currently using kennel cough vaccines, says Christopher Pappas Jr., DVM, director of companion animal technical services for Intervet/Schering-Plough. "You find the same risk factor in those groups of dogs — the ones that go to doggy day care, that are boarded often or are involved in dog shows."

    Rozanski agrees: "I think the best advice for veterinarians is to look at the risk for each dog and look for the regional risk, then update your vaccination guidelines."

    Although cases of CIV are not as widespread as cases of influenza in humans, continued vigilance is necessary to keep the risk of outbreaks in check. Not enough is understood about the mutation rate of the virus in dog populations to predict its behavior in the future.

    "Influenza behaves differently in each species," Pappas says. "In humans, vaccines are updated annually to predict which strain is going to hit the following year. In horses, the vaccines are updated about every 5 to 7 years. Canine influenza is a new disease, so instead of adding strains to the vaccine, we are monitoring the vaccine in the community to make sure it cross-protects with the new strains that develop, and we will update as necessary. Based on the science, history and research judgment [of CIV], I would think that the CIV vaccine will probably not need to be updated yearly. It's important to monitor."

    The future

    The field of shelter medicine has undergone a phenomenal growth in the past few years, which will be beneficial for monitoring and protecting dogs from diseases like CIV.

    "Shelters do phenomenal things now," Rozanski says. "They do a lot of good studies that help the world. As small animal practitioners, we tend not to think too much about 'herd' health, but the emerging shelter medicine field is a great opportunity to look at that. Most of the vaccines are not terribly expensive, but on a multiple-animal basis that adds up. I think the questions we don't tend to ask in veterinary medicine are about cost. How many animals do we have to vaccinate to prevent one dog from getting sick, and is that cost effective? In human medicine they do those studies on a regular basis, but we tend not to. It would be very helpful to know these sorts of things."

    Dr. King is a member of the Intervet/Schering-Plough Animal Health speaker bureau and receives honoraria from the company for presentations. Dr. Rozanski is currently conducting research sponsored by Intervet/Schering-Plough that is unrelated to the influenza vaccine.

    NEXT: Gibbons named Exotic Vet of the Year

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