A rash of news reports late last year about outbreaks of canine influenza left the impression that dogs in various parts of the United States were at imminent risk of catching the flu during the winter holidays.

A look at dog-flu diagnoses documented by major veterinary laboratories suggests that the reality was less dramatic and more nuanced. Some veterinarians believe aggressive marketing of dog-flu vaccines was behind the hype.

The New York City metropolitan area did have a bona fide outbreak and continues to experience documented illness, according to information from Cornell University Animal Health Diagnostic Center, Idexx Reference Laboratories, and Antech Diagnostics, the veterinary diagnostic laboratories most likely to test samples from suspected canine influenza cases around the country.

Idexx detected a spike in activity in Texas and California, as well. However, those spikes occurred between August and October, said Dr. Christian Leutenegger, head of molecular diagnostics for Idexx. He said the outbreaks appeared to be short-lived. By the time news accounts circulated in late December, things had calmed down in those regions.

Reports also named Colorado and Massachusetts among the regions with confirmed cases but government officials in those states told the VIN News Service that the occurrences did not constitute outbreaks.

Dog flu is considered enzootic, or generally present, in Colorado. Massachusetts received reports of two cases of canine influenza in 2011, but they happened two months apart — one in October and one in December — and therefore appear to be unrelated, said Michael Cahill, director of the Massachusetts Division of Animal Health.

“When there’s no epidemiological link between the two cases you can’t call it an outbreak,” Cahill said.

Some veterinarians suspect that vigorous marketing of canine influenza vaccine plays a part in confusing perceptions of disease prevalence.

“It seems to be getting harder to (determine) when a disease is real and when it is being ‘pushed’ by vaccine or drug manufacturers these days,” commented Dr. Margaret Mason, a practitioner in Carpenteria, Calif. Mason posted her thoughts on the Veterinary Information Network (VIN), an online community for the profession.

A number of Mason’s colleagues have expressed similar sentiments on VIN. Several related anecdotes about and experiences with Merck Animal Health, maker of one of two canine influenza vaccines on the market, pressing boarding kennels and shelters to require or administer the vaccine routinely.

Merck confirmed that it markets the vaccine through “education of boarding facility operators, kennels, pet owners and veterinarians about the disease state and about steps they can take to encourage prevention.” Told that some practitioners are concerned about overzealous marketing, a company media-relations official had no comment.

Dr. Cynda Crawford, a veterinarian at the University of Florida (UF) who led the research team that first identified the canine influenza virus in 2004, said that regardless of Merck’s role in calling attention to the disease, documented infections are occurring. She said the company is making worthwhile contributions to scientific understanding of the disease.

“It’s an accepted practice for different pharmaceutical companies to market their wares. I view their interest in canine influenza as a valuable asset to the veterinary community," she said. "Merck Animal Health has taken an active role in tracking canine influenza in an effort to provide updates on where it is occurring. In addition, their tracking provides opportunities to acquire field isolates for analysis to determine whether the virus is mutating in a way to affect diagnostic test accuracy (and) vaccine efficacy."
 
Crawford, along with colleagues at UF, Cornell University and the U.S. Centers for Disease Control and Prevention (CDC), share intellectual rights to the virus; Merck has licensed the right to use the virus to make a vaccine. However, Crawford noted, she and the others do not receive compensation from vaccine sales.

A mutated form of the equine influenza virus, the H3N8 canine flu virus has been found to affect dogs in much the same way that flu viruses typically affect people and horses: causing a runny nose, cough and fever but usually able to be shaken off with rest and time. But in some dogs, regardless of age and health status, Crawford said, the flu may progress to pneumonia. "There is no way to predict which ones will" be stricken with more severe illness, she said.

Dog flu isn't known to transmit to humans, just as dogs don’t usually catch flu from people — an exception being the dreaded H1N1 influenza virus that has sickened humans, livestock, zoo inhabitants and house pets alike.

As for protecting dogs against the H3N8 flu bug, the American Animal Hospital Association’s latest Canine Vaccination Guidelines list the canine influenza virus (CIV) vaccine as a “noncore” immunization, to be used only when conditions warrant.

“The CIV may be recommended (noncore) in selected shelters located within endemic communities or in shelters that transport dogs to or from communities considered to be endemic for canine influenza,” the guidelines state.

They continue: “This is a killed vaccine that requires two doses be given at least two weeks apart. Immunity is expected one week after the second dose. Therefore, even in shelters located within endemic communities, the benefit of this vaccine will be limited if exposure cannot be prevented before onset of protection or in dogs unlikely to stay long enough to receive the full series of vaccines.”

Both vaccines on the market require a booster after the initial shot to stimulate the immune response. The manufacturers recommend annual vaccination thereafter.

Veterinary infectious disease experts generally advise vaccinating dogs that travel regularly to venues where dogs congregate, such as shows and racetracks, as well as dogs in regions with a documented outbreak.

Some veterinarians also advise vaccinating dogs before they’re boarded and dogs that frequent dog parks. However, other practitioners consider that unnecessary.

A-Animal Clinic in Fort Worth, Texas, began in mid-November to require that all dogs left at the facility — whether for boarding, day camp, grooming or medical procedures — be vaccinated against canine influenza virus.

Practice Manager Newley Spikes said he and his wife, Dr. Karen Spikes, established the policy after receiving information from Merck about confirmed flu cases in their region.

He said the vaccine vendors “pounded us with the information. We’re one of the largest boarding facilities (in the area); we hold 150 dogs. They’ve been after us for about 24 months or so that we need to get on board with CIV. They continue to bring it to our attention if there are cases anywhere.”

Spikes, who co-owns the clinic with his wife, said the vaccine requirement makes good business sense. “In August 2007,” he recalled, “we had something go through our kennel, an upper-respiratory (infection) — drippy eyes, green stuff out of the nose and cough that was persistent. We treated hundreds of dogs. It cost us, net giveaway, the cost of drugs, something like $10,000. If they get sick here ... if they get hurt here, we take care of it without charging.”

Spikes said he doesn’t consider Merck’s vigorous marketing inappropriate. “Frankly, they aren’t pushing it hard enough, if you ask me,” he said. “... We are in business here, and our business is animal care. ... If there’s a (method of) prevention that’s easy and safe and economical to the client that could keep an outbreak from taking place in a facility such as ours, we should be on it.”

Spikes said the clinic charges $19.85 for the first shot and the same for the booster. “Our clientele has been nothing but receptive,” he reported.

Although it takes a week following the booster for the vaccine to confer immunity, Spikes said his facility’s requirement is met as long as the dog receives one shot. That shot may be administered immediately before the dog is admitted.

He acknowledged that requiring only one shot upon admittance doesn’t actually protect the dog, but said that to demand dogs be fully immunized before check-in is impractical. “In a business situation, perfection isn’t an option,” Spikes said.

The goal, he said, is to get patients and boarders protected over time. Spikes estimated that more than 1,000 of the facility’s canine patients and visitors have completed the two-shot series.

The Merck canine influenza virus vaccine, dubbed Nobivac Canine Flu H3N8 — developed by Intervet/Schering-Plough Animal Health, which is now owned by Merck — was available for the first time in 2009 under a conditional license from the U.S. Department of Agriculture. A full license was granted the following year.

A second canine influenza virus vaccine made by Pfizer Animal Health, called Vanguard CIV, went on the market last February. Dr. Oliver Knesl, marketing manager for companion animal biologicals at Pfizer, told the VIN News Service that his company’s marketing efforts focus on educating practitioners about how the virus works in tandem with other pathogens that cause respiratory disease in dogs.

“It can be a primary pathogen and cause disease on its own, but it’s very much (also) a participant along with some of the more traditional canine respiratory pathogens (such as) Bordetella bronchiseptica, canine adenovirus type 2 and parainfluenza,” Knesl said.

Dr. Edward Dubovi, director of the virology laboratory at the Cornell University Animal Health Diagnostic Center, agreed that tracing the cause of respiratory disease in dogs has become complicated.

"The issue of pathogens involved in 'kennel cough' is now very complex," Dubovi said, referring to a syndrome formally known as canine infectious respiratory disease or acute respiratory disease of canines.

"Prior to 2003, all one talked about was Bordetella and canine parainfluenza virus with some mention of canine adenovirus and mycoplasma," he said. "Since 2003, we have at least four new viruses in respiratory cases in dogs, two of which are the most common viral infections in dogs: canine respiratory coronavirus and canine pneumovirus. Dogs in group housing are often infected with multiple agents such that it is difficult to determine if one is more important than the other."

Crawford at UF concurred. She said she has tested hundreds of dogs in respiratory disease outbreaks and found co-infections to be "very common."

The relatively short history of canine influenza virus makes it all the more challenging for practitioners to sort out the facts, since researchers still are learning how the virus behaves. For example, unlike human flu, canine influenza does not follow a season. That’s another confounding factor in tracking its spread.

“Where canine influenza virus appears, in what community, is totally unpredictable and sporadic,” Crawford observed.

Furthermore, no single agency or institution tracks the virus. In veterinary medicine, there is no equivalent of the CDC.

According to Merck, the virus has caused illness in 38 states. That information is gleaned from five disparate sources.

Idexx and Cornell offer their respective data on canine influenza virus test results with the caution that the information isn’t comprehensive. Said Idexx’s Leutenegger: “Even though we receive large numbers of samples, it is difficult to determine prevalence due to the low number of cases submitted in a particular geographic area.”

Of the three laboratories believed to evaluate the majority of samples from suspected canine influenza cases, Idexx had the most varied information on positive results in 2011.

Dr. David Lewis, director of consultation services at Antech Diagnostics and a consultant on VIN, said his lab has seen no unusual flu activity outside of the New York City area in the past six months.

Dubovi at Cornell reported seeing an uptick in positive results from greater New York City as well as cases from a single kennel in San Antonio, Texas.

Leutenegger said Idexx noticed spikes in California; New York City and environs; and Texas, all occurring in August, September and October, as follows:

• California, eight cases. Five in the Los Angeles area, three in the Sacramento area.

• New York region, 10 cases. Three were in New York City, three on Long Island, and one each near Poughkeepsie, N.Y., Middletown, N.Y., Hartford, Conn., and Delaware.

• Texas, 10 cases. Five were in San Antonio, five in Dallas/Fort Worth.

Leutenegger said clusters of cases occurring in a relatively short period within a particular geographic region stand out because positive results on canine influenza tests typically pop up in more scattered fashion. For example, last July, Idexx detected five positive samples. Two were from Connecticut, one from Arizona, one from North Carolina and one from Texas.

Because canine influenza virus prevalence is not very high overall, Leutenegger said, attention-getting peaks can form easily from a relatively small number of cases.