As the H3N2 strain of canine influenza circulates beyond Chicago, Illinois and spreads to other Midwestern states — Wisconsin and Indiana among them — one expert says it isn’t the virus’ endurance or speed that’s significant.
It’s the fact that it crossed the U.S. border.
“We have absolutely, without a shadow of a doubt, proof that a foreign animal disease has been imported into the U.S.,” Dr. Ed Dubovi said. “I don’t think anyone can look at this situation and say we’re protecting our animal population the best we can.”
An estimated 1,300 dogs have been afflicted. The virus is blamed for at least six canine deaths.
Dubovi, a Cornell University professor with a master’s degree in virology and doctorate in microbiology, is one of the nation’s leading experts on canine influenza. It was at Cornell’s Animal Health Diagnostic Center, which Dubovi directs, that the first influenza virus known to infect dogs was isolated, in 2004. The pathogen was an influenza A virus subtype H3N8, a different strain from the one now circulating in the Midwest. The diagnostic discovery stemmed from research conducted at the University of Florida on a novel respiratory disease that had felled racing greyhounds.
H3N8 has since spread across the United States much like flu viruses in humans — via direct contact with infected aerosolized respiratory secretions and contaminated objects.
H3N2 is traveling much the same way. According to Dubovi, the virus is closely related on a molecular level to strains that are circulating in Chinese and South Korean dog populations. H3N2 canine flu emerged in that region in the mid-2000s. Like dogs, cats are susceptible. There is no evidence that this particular H3N2 subtype can be transmitted to humans (though other strains do infect humans).
Dubovi said he’s had an eye on H3N2 since 2008, when he read about it in scientific literature out of South Korea. The virus, he suspects, might have been imported via an infected dog from Asia.
“My concern all along was that someday this virus might make its way here,” he said. “We don’t know how it happened, but it certainly could have come from a dog or a cat. There are multiple international groups who are rescuing dogs from the meat market in Korea and shipping them into the U.S., and we have sketchy quarantine requirements if any at all. Restrictions on the movements of companion animals across borders are somewhat nonexistent.”
The United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) strictly govern the movements of food-producing animals. The Centers for Disease Control and Prevention is charged with overseeing the importation of most dogs, cats, birds and several other species.
Dog importation rules appear to be focused on preventing the admission of dogs potentially infected with rabies or screwworm only.
USDA calls for the additional screening of collies, shepherds and other dogs used to herd livestock, sometimes quarantining the canines until they’re declared free from tapeworms.
Regulatory officials from either agency did not respond to inquiries about whether tighter importation rules might have kept H3N2 at bay.
“I’m sure USDA and everybody will say, ‘No, we do a good job protecting the country,’ ” Dubovi said. “But how do you explain how it got here? It didn’t fly over on a bird. This virus is highly adapted to dogs, even if it has an avian origin.”
H3N2 is a hodgepodge of various flu strains, borrowing sequences from others, with its closest linkage to avian influenza found in Asia. “Flu does recombine, and it recombines in a lot of different formats,” Dubovi explained.
He describes H3N2 as a “bit more pathogenic” than H3N8, noting that, “obviously the Chicago outbreak caught us all a little flat-footed.”
The virus’ hallmark is its scope and rapid spread. “If you have a kennel with 100 dogs and 50 are sick, you can bet this is canine flu,” he said.
He added, “No other pathogen travels that explosively in a group of dogs.”
Around 8 a.m. Saturday April 11, phones lit up at Animal Medical Center of Chicago.
One after another, calls came in from owners whose dogs were coughing, sneezing and generally unwell. Dr. Donna Solomon, owner of the practice, made a gut decision to see only the infirm that day.
“It was the best thing we ever did,” she recalled. “We recognized early that we wouldn’t be able to service both our well and sick patients.”
The culprit: canine influenza.
Solomon's first clue that the virus was in the area occurred three weeks earlier. “I was seeing what I thought was kennel cough. Then one Tuesday I saw a pet with a 105-degree temperature and I thought, ‘This is not traditional kennel cough.’
“Then a lot of feverish dogs starting coming in,” she continued. “We had rooms designated for coughing animals.”
Both H3N8 and H3N2 can cause high fever, loss of appetite, coughing, nasal discharge and lethargy. Symptoms often are more severe in cases caused by the H3N2 virus, yet it has a low mortality rate.
After seeing about 100 to 125 coughing dogs in the last three weeks, Solomon said she knows what to expect: “These canine influenza dogs get hit harder and are taking much longer to recover. We’re dispensing 10 to 14 days' worth of cough suppressants and 14 to 21 days of antibiotics for patients (to treat secondary bacterial infections).”
That’s double the amount of medication Solomon typically prescribes to tackle H3N8. Practicing in the heart of the outbreak, she suspects that government estimates of 1,300 or so stricken dogs are low.
“No one has ever seen anything like this,” she said. “It was actually bigger than what they think it is.”
Dr. Bruce Silverman also thinks the estimates are “far too conservative.” The owner of Village West Veterinary said he’s seen multiple cases a day for weeks.
“I’m not sure what constitutes ‘epidemic,’ but this is unlike anything I’ve seen before,” he wrote in a discussion on the Veterinary Information Network (VIN), an online community for the profession. “Fortunately, most dogs have been successfully treated with minimal antibiotics and more supportive care for their fever, lethargy and inappetence ...”
Testing for the virus also is atypical. “Veterinary professionals are advised that diagnostic testing of samples from sick pets can be done using a broadly targeted influenza A matrix reverse transcriptase-polymerase chain reaction assay,” or Rt-PCR test, a Cornell press release said.
Cornell officials advise veterinarians to seek diagnostic labratories with the ability to specifically look for H3N2, given that the H3N8 Rt-PCR will not work for the H3N2 strain.
An existing serologic test for H3N8 is considered ineffective because of differences between the two viral strains. An H3N2-specific serologic assay is now available at Cornell.
So far, Dubovi’s office has processed 350 or so samples during the past two weeks, and he gets inquiries by the day, often spending four to five hours on the phone about suspected cases.
“What we’re getting in (from veterinarians) is the canine respiratory panel; a panel of eight PCRs. We’re running them daily. Normal turnaround time for results is 48 hours on a respiratory panel. Now it’s probably 72 hours, maybe more if we’re backed up,” he said.
For any respiratory virus, early collection is critical for accurate test results. Influenza viruses in particular are “in and out quickly,” Dubovi explained. “There’s no latent carrier state.”
“We’re recommending taking nasal or throat swab cultures between the first four days of the onset of clinical signs,” he said. “The latent period between infection and clinical signs is two days. By four days post infection, you’re almost at the peak of virus production. But then the immune system kicks in, so by day seven, the amount of the virus in the system is falling rapidly.”
Other laboratories also are testing canine influenza cases. Kansas State University (KSU) Veterinary Diagnostic Laboratory is one of them, offering a 17 percent discount on its canine respiratory panel due to the “possible epidemic.”
“The sample that is needed is a nasopharyngeal swab transported in viral media transport or a small amount of sterile saline,” a KSU press released explained. “Expected turnaround time is 24 to 36 hours. ... It is important to identify the pathogen(s) to manage respiratory disease appropriately.”
Several years ago, the emergence of H3N8 prompted the manufacture of two vaccines, one marketed by Zoetis and the other by Merck Animal Health.
What, if any, immunity those vaccines can provide against H3N2 is unknown though many scientists believe any cross-protectively is likely to be minimal considering that current tests for H3N8 cannot detect the newly emerging virus.
“It’s a very different strain,” Dr. Alice Wolf, a board-certified internist with a special interest in infectious diseases, explained in a VIN discussion. “That is why the H3N8 test did not detect it. If the antibody did not cross react on the test, it’s not going to cross react in the dog.”
Dr. Keith Poulsen of the Wisconsin Veterinary Diagnostic Laboratory, which also is conducting tests on H3N2, agrees that vaccines based on the H3N8 strain are unlikely to be efficacious for H3N2.
He says there’s no harm in inoculating anyway.
“… The H3N8 strain is still circulating, and there might be some cross reactivity,” Poulsen said. “While the vaccine's efficacy against the H3N2 is unknown at this time — there are no controlled studies — it has a low likelihood of side effects that would hurt dogs. It's one of our recommendations.”
Officials with Merck did not directly respond to queries about whether a newer version of its canine influenza vaccine is in the works, saying only, "We continue to be actively engaged in this very fluid situation and are working on all possible fronts to determine the best short- and long-term solutions."
Zoetis communications manager Colleen White was more specific: "While we can’t speculate on exact timing of a potential vaccine, we are actively pursuing development of a vaccine to address the H3N2 virus in dogs. Development of this vaccine is currently one of our highest priorities at Zoetis."
Meanwhile, H3N2 cases seem to have ebbed in Chicago, where the virus first reared. Officials in Michigan say the new strain hasn’t crossed the state line, and suspicions of an outbreak at a shelter in Georgia were quelled after test results showed pneumonia to be the condition.
Solomon, the practitioner in Chicago, said she now sees fewer canine influenza cases and credits media reports on H3N2 for helping to contain the virus.
“I strongly believe this news coverage helped increase pet owners’ awareness of this serious infectious disease outbreak,” she said on VIN. “Our Chicago pet owners knew to avoid dog parks, grooming parlors, day-care facilities … as a result of reading these articles and watching the television news.”
Some in the profession aren’t as complimentary. On Facebook, the Ohio Veterinary Medical Association (OVMA) discredited media reports that H3N2 had made its way to the Buckeye State.
“At this time, the OVMA is not aware of any confirmed cases of canine influenza in Ohio,” officials posted last Friday. "We also want to stress that in spite of being termed ‘deadly,’ the mortality rate for infected dogs is quite low.
“ … Please remain calm — and as always, take your local news stations with a grain of salt.”
VIN News Service commentaries are opinion pieces presenting insights, personal experiences and/or perspectives on topical issues by members of the veterinary community. To submit a commentary for consideration, email firstname.lastname@example.org.