Canine Influenza – Just When You Think You Knew It All
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Just When You Think You Knew It All, Everything Changes!
by Amy Fernandez
As if we didn’t have enough to worry about, the media has now alerted us to a newly identified strain of dog flu, which they consistently characterize as deadly. This isn’t the same dog flu that sparked waves of alarmist reports back in 2005. The prelude to the current drama was ultimately labeled as an offshoot of equine influenza A, subtype H3N8. First documented over 40 years ago, the canine version of the virus first emerged in racing Greyhounds in 2004.
Panic was unleashed a few months later when experts announced that America’s canine population confronted a new, highly contagious, potentially lethal pathogen. In some respects, this fear was legitimate. Since it was the first dog-specific strain of H3N8, no one was immune. It was open season.
Ensuing research revealed that the H3N8 canine influenza virus (CIV) had been bubbling under the surface for years before it hit the headlines. Because the initial outbreak occurred at a Florida track where both horses and greyhounds were raced, this location was considered ground zero where the mutated strain evolved and jumped the species barrier. That detective work also explained waves of unidentified respiratory disease outbreaks at that location dating back to 1999.
About 15 percent of infected dogs were asymptomatic. Another eighty percent experienced mild flu symptoms two to five days after exposure and remained contagious for seven to ten days. Approximately five percent became seriously ill, developing secondary bacterial pneumonia. Ultimately, fatalities within the general pet population were under one percent and about five percent among the racing Greyhound populations where it first emerged.
Frequently, the associated fever, lethargy, nasal discharge, and persistent cough were misdiagnosed as kennel cough, which of course also carries the risk of secondary bacterial infection. However, a test soon became available to ID the virus, known by the catchy moniker of influenza A matrix reverse transcriptase-polymerase chain reaction assay, or the H3N8 Rt-PCR test.
Polymerase chain reaction technology is widely regarded as a premier diagnostic tool of molecular genetics. Among its many uses it has made it possible to identify viral strains and engineer appropriately targeted vaccines in record time. USDA approved the first (CIV) canine influenza vaccine in June 2009. Initially administered in two-biweekly doses, like other flu shots, annual revaccination is needed. Of course we know that isn’t the end of the story.
These innovations also allowed researchers to ID virus lineages via DNA sequencing and trace them back to the starting gate. This technological bag of tricks stems from the development of the polymerase chain reaction (PCR), the rapidfire amplification of DNA fragments. Now considered the standard approach to genetic research, it was the brainchild of researcher Kary Mullis. A dedicated dabbler in hallucinogens, Mullis always credited this penchant for the insights that led to his breakthrough discovery and subsequent 1993 Nobel Prize in chemistry.
Like every other aspect of this flu situation, that backstory suggests that a conventional, straightforward approach isn’t invariably the quickest route to the finish line.
Viruses rank among the planet’s most pervasive pathogens and we are only beginning to comprehend precisely how persistent and creative these microbes are. Their evolution outpaces every other life form and, in a way, we encourage it. Constant mutation is their default survival strategy to stay a step ahead of the immunological creativity and determination of their hosts. This endlessly escalating pathogenic arms race explains why we face brand new exotic flu strains every winter and pretty much ensured that H3N8 dog flu wasn’t destined to be a one act show.
Viruses forever revise their offensive strategies by mutating and recombining via subtle genetic rearrangements. The highly pathogenic avian flu currently upending America’s poultry industry offers a good example. This year’s culprits have been identified as strains of H5N2 and H5N8. So far, their damage doesn’t approach the 1984 bird flu epidemic that decimated the Northeast but that may change by the end of 2015. It is currently spreading beyond the epicenter of devastation, coincidentally the same Midwestern states hosting the latest dog flu outbreak. Needless to say, that’s not the main reason why bird flu makes the news these days. Today, five avian flu subtypes are recognized as highly pathogenic in humans.
Human flu viruses regularly change it up with avian and swine strains. That genetic card trick has been the source of three flu pandemics since 1900 including the deadliest disease epidemic in human history, the 1918 Spanish Flu which killed over 21 million.
These microbial double agents are old news. To put it in perspective, the granddaddy of flu microbes started out as an adapted strain of swine flu in China over 10,000 years ago.
This ability to infiltrate defensive barriers that normally prevent interspecies transmission has been the source of most human infectious diseases. Some are rare, some ubiquitous. Approximately 26 originated in poultry, 32 in rodents, 35 in horses, 42 in swine, 46 in sheep and goats, 50 in cattle, and 65 came to us special delivery from dogs- emblematic of the long relationship between our species.
From an immunological standpoint, an onslaught of dog flu was preordained, especially because of the epidemic proportions of the first round. Its clean sweep through a population with no prior exposure virtually guaranteed the eventual emergence of a second deployment.
The latest strain threatening dogs (and cats) is a cocktail of human and avian flu, closely related to the Asian H3N2 dog flu documented in southern China, South Korea, and Thailand in 2007. A few veterinary sources have expressed surprise at its rapid global reach despite efforts to restrict its spread. Of course, post-Ebola/West Nile Virus, etc. that shouldn’t really surprise anyone.
To date, about 1,300 cases have been diagnosed in Illinois, Wisconsin, Ohio and Indiana. Most of them have been mild, resolving in two to three weeks. And like any respiratory infection, pneumonia is a potential, but rare complication. So far six fatalities are documented. Some experts advocate tightened restrictions regarding international transport of livestock and companion animals. However, such measures are unlikely to seriously impede the spread of a pathogen like the flu virus.
Spread by the usual modus operandi, it’s typically contagious before obvious symptoms emerge. Viruses have another notable advantage when it comes to contagion potential. Unlike cells, they can dry out and reactivate when they come in contact with a potential host. And this one survives on surfaces for 12-24 hours.
From that perspective, dogs are ideal vectors and hosts considering the densely packed environments and obsessively tactile olfactory habits they favor. The traditional spectrum of situations where viruses flourish– dog tracks, shows, grooming shops, etc. have been augmented in recent years by an entirely new platform of social gatherings. Daycare, dog parks, meetups, and a host of other interactive doggy communities not only facilitate direct contact, they encourage it.
Once again, the media has worked its usual magic. Concerned owners in regions with no reported cases have been stampeding to the vet for CIV vaccinations, even though there is no evidence that the current shot offers any protection against this new strain.
Arguably, this demonstrates a commendable sense of responsibility and caring. It’s also ironic and possibly misplaced considering that a growing percentage of these owners opt to forego routine DHLPP vaccinations for the same reasons that many parents decided their children are better off without measles vaccinations. That works up to a point – the point where herd immunity inevitably breaks down and leads to the measles and whooping cough outbreaks currently making news. More importantly, even though news reports repeatedly characterize H3N2 as deadly, it is nothing like the 90 percent mortality rates of the 1970s parvo epidemic. At least one manufacturer is currently developing a canine H3N2 vaccine. By the time it hits the marketplace, it’s likely that new strains of canine flu will emerge to divert its impact.
So far, there has been no cross pollination between human and canine flu strains but brace yourselves, viral adaptation is not an exclusive arrangement. Sooner or later, man will be sharing flu bugs with his best friend. On the other hand, who else would you want keeping you company when you land in bed with the flu?
Short URL: http://caninechronicle.com/?p=82858
Posted by ralbee
on Jul 23 2015. Filed under Current Articles, Editorial, Featured.
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