At least 75 dogs in Georgia, most around Atlanta, were infected with an H3N2 influenza virus following a larger outbreak this spring in the Chicago area.
Pharmaceutical companies have been developing vaccines against the Asian strain of influenza A H3N2 virus, which was found for the first time in the U.S. this year. Existing vaccines were designed to protect against H3N8 strains that have circulated among U.S. dogs during the past decade, and analysis from the University of Illinois Veterinary Diagnostic Laboratory indicates those vaccines are unlikely to provide substantial cross-protection against H3N2.
The virus was identified as the cause of an outbreak of acute respiratory disease affecting more than 1,000 dogs this spring in the Midwest, primarily in and near Chicago, according to information from Cornell University. It originated in southern China and South Korea and was derived from an avian strain.
Dr. Edward J. Dubovi, director of the virology laboratory at Cornell University’s Animal Health Diagnostic Center, said in late June that reports of a canine influenza outbreak in Atlanta indicated that dogs there had an H3N2 virus infection consistent with the virus in Chicago’s outbreak, and sequencing would indicate whether the virus in Atlanta was an extension of the earlier outbreak or a separate introduction of H3N2 into the U.S. Reports of infections in the Chicago area were in decline by then, he said, but many veterinarians seeing new infections may have been familiar enough with the virus that they stopped submitting samples to diagnostic laboratories.
“There certainly was a lingering effect in the shelter system,” he said.
A July 7 update from the Athens Veterinary Diagnostic Laboratory at the University of Georgia states that tested samples from 75 of 230 dogs were positive for H3N2. The early cases were from the Atlanta metropolitan areas, and later ones were from other counties in Georgia.
Dr. Dubovi said, “Depending on the facilities that are affected and who’s moving dogs where, this could expand even further.”
Spokeswomen for Merck Animal Health and Zoetis, which produce canine vaccines against H3N8, provided statements that neither company had indications of whether their vaccines provided cross-protection against the Asian strain of influenza A H3N2 virus. Each said her company was developing a vaccine against H3N2.
Results of genetic analysis at the U of I laboratory indicate the hemagglutinin protein of an H3N2 virus isolated from a dog that died of pneumonia was only approximately an 85 percent match to the hemagglutinin proteins of H3N8 virus that was circulating among dogs from 2003-2013, according to information from the University of Illinois College of Veterinary Medicine. The virus isolated from the dog was found to have 98 percent nucleic acid identity to H3N2 found in Asia.
Dr. Gail Scherba, a veterinary virologist and professor in the college, said the analysis was a simple comparison of the H3 proteins used by the viruses to attach to host cells. The number of differences was substantial enough to cast doubt that commercial vaccines could provide cross-protection, and she cited as evidence that some dogs sickened by the 2015 outbreak had been vaccinated with a H3N8 vaccine.
In a notice she distributed in May for the benefit of veterinarian clients of the laboratory, she wrote that current vaccines were “unlikely to offer significant cross-protection against the Asian H3N2 strain.”
Dr. Dubovi said that, on the basis of experiences with minor variations that circumvent cross-protection by human-use influenza vaccines, one could expect that vaccines designed for H3N8 viruses would provide little protection against the H3N2 virus. But it remains unclear whether vaccinated dogs could show lesser clinical signs from infection.
“As far as I’m aware of, we don’t have a clue whether the vaccine is beneficial,” he said.
Where both viruses are present, such as in the New York City area, he recommended administration of the H3N8 vaccine to prevent dual infections.
Nasty, continuous problems
Mortality rates among H3N2-infected dogs have been low, Dr. Dubovi said. While media reports have noted six dog deaths in the Chicago outbreak, he thinks it likely that five times as many dogs had infections as the 1,000 reported.
In H3N8 infections, he said, deaths usually involve complications such as coinfections or infection with commensal pathogens. The H3N2 virus was the only pathogen detected in the lungs of some dogs that have died during the outbreak, which he said was concerning.
“But it certainly hasn’t been a large number of dogs that came in with that kind of a presentation,” he said.
Veterinarians may have difficulty telling whether a dog entering a veterinary clinic with respiratory signs is infected with, say, influenza, a betacoronavirus, or another pathogen. For veterinarians seeing “kennel cough,” it’s critical to get a history of that dog’s travel over the past week.
Dr. Dubovi also urged caution among breed rescue organizations that move dogs to new locations across the country, especially when those dogs are handled by multiple caregivers along the way.
Dr. Scherba expects the H3N2 virus will continue circulating among dogs beyond the current outbreak, and she noted the H3N8 virus has been circulating in the U.S. for more than a decade. Influenza viruses are interesting, nasty, continual sources of problems, she said.
Dr. Dubovi similarly described influenza viruses as mosaics of mutations and reassortments with potential ranging from the virus becoming extinct to causing enduring harm. The world is becoming more aware that dogs can be infected with a multitude of avian influenza strains, even though dogs were not among influenza concerns prior to 2004.
While dogs have less involvement than do, for example, pigs in the evolution of influenza viruses, he said dogs can pick up and scramble influenza viruses’ genetic material under the right circumstances.
Related JAVMA content:
Chicago responds to canine influenza (June 1, 2015)