For years, poultry producers have been breeding something in their barns other than birds.
Long present in wild bird populations, the low-pathogen version of the virus has entered barns, remaining there until a series of mutations turned into something else — something deadly.
“We have been playing with fire,” said Earl Brown, a professor emeritus at the University of Ottawa, who spent most of his career studying the relationship between birds and viruses.
He said high-density methods of poultry production have created an ideal environment for the influenza virus to change, mutate and adapt.
“If you uptake a lot of a virus and put it into an animal, and then you take the bit of virus that grows and you put it into a new animal, and you keep doing that over and over again… the virus becomes a killer,” he said.
“The same sort of thing happens in a poultry barn — you get a wild virus, you’ve got a lot of birds housed close together, so the virus doesn’t have to jump very far to the next bird. It’s not a natural situation, but it is a situation where you get the evolution of high virulence and so it’s always a bit of a powder keg.”
Not all die
All mammalian influenza viruses originate in birds, but not all birds infected with influenza die, or even get sick, he said. However, many will become carriers of the virus, spreading it as they migrate throughout North America.
“Wild bird populations, particularly waterfowl and migratory birds, have acted as a reservoir for avian influenza for a very long time, which means they’ve had the ability to develop immunity to avian influenza viruses and they’ve adapted,” said Dr. Megan Bergman, the province’s chief veterinarian.
Wild birds that don’t adapt will die, she added, but noted that number of deaths in wild birds is fairly low.
Domestic flocks of birds, whether it be ducks, chickens or turkeys, also have the ability to recover from low-pathogen forms of the virus in some circumstances, although turkeys tend to be most susceptible to the disease. However, even birds with the potential to recover are culled, primarily to prevent a low-pathogen form of the virus from mutating into a highly virulent, highly pathogenic one.
Potential survivors culled
The first outbreak of highly pathogenic bird flu in North America occurred in the 1920s and was unrelated to wild birds. It was caused by the unintended release of a European virus by a laboratory. But the first naturally occurring avian virus to make waves was a low-pathogen influenza in Manitoba in 1953.
“It wasn’t a full-blown high-path bird flu, but it was killing ducklings, which sort of got it on the map,” said Brown.
But by 1966, a highly virulent form of the disease made its debut appearance on an Ontario turkey farm, forcing turkey production into the barn and out of the field.
The year 1997 marked another milestone. It was the year H5N1, or Asian bird flu appeared on the scene. By 2005 the virus had made its way to North America, meaning that a highly pathogenic, highly virulent form of bird flu was now present in wild bird populations. An influenza so adapted to domestic poultry it was ready to kill as soon as it entered a barn.
“Up until the Asian situation, the wild bird viruses would move into a poultry barn, become highly pathogenic, you’d clean up, decontaminate and start again — that virus would be eliminated,” said Brown. “But what happened in Asia, was the virus became highly pathogenic… they were seeing it out killing wild birds and they found it in wild birds. So you had a virus that had gone from wild birds to poultry, killed poultry, had then gone back to wild birds and was able to hang around in wild birds, so that’s very unusual.”
Today that H5N1 virus has given rise to the H5N8 virus, the same highly virulent strain that has infected many poultry barns in the United States, where more than 38 million birds have been culled at 170 barns.
Yet Canadian producers have only seen a slight impact as a result of the current outbreak, despite being traversed by the same migratory bird paths as the U.S. Two farms in Ontario where infected earlier this year, but so far the virus hasn’t spread significantly north of the border.
Some suggest this has to do with different husbandry practices, particularly the size of American poultry operations, which can see flocks as large as a million birds.
“Certainly, density is a huge player in this particular type of issue, because they have many more barns with much higher numbers of birds than we typically see here in Manitoba; that puts them at higher risk,” said Bergman. “And when barns are very close together and you have a high level of virus in circulation, it’s easier to transmit it.”
Another factor is that several barns may be operated and managed by the same person or persons, creating opportunities to spread the disease through unwitting human intervention.
The chief vet added that having smaller barns, located farther apart and managed by different farmers greatly decreased the risk of disease spreading.
Steve Leech, national program director for Chicken Farmers of Canada, said that Canada’s stringent on-farm food safety programs could also be playing a role in keeping influenza out of Canadian barns.
“I can’t speak to all the differences between the U.S. and Canada, but certainly with the past outbreaks of avian influenza we’ve had we’ve increased our biosecurity and changed some of our biosecurity protocols, it’s been a focus of the Canadian industry,” Leech said. “So we have biosecurity requirements that are mandatory… that food safety program isn’t just a management tool for farmers, it’s enforced in all 10 provinces and 100 per cent of our farmers are certified on that program.”
Others have suggested it’s the fact that Canada’s poultry sector is supply managed that has spared farmers the intense losses experienced south of the border where operations are often vertically integrated.
Currently, the Canadian Food Inspection Agency is preparing a report on the outbreak, as are American counterparts. Leech hopes this will provide more answers to questions about how the disease is spreading and why U.S. producers have been so hard hit.
In the meantime, all poultry producers are being encouraged to remain focused on biosecurity. There has also been talk of breeding more resistant poultry breeds and incorporating more genetic diversity into commercial flocks.
But Brown said those measures might just be too late.
“The horse is out of the barn,” he said, adding that changes to husbandry practices might have been more effective prior to the introduction of Asian avian influenza.
“I’m a bit flabbergasted at the size of the holding in the United States, where they have multimillion birds on one farm. Even with multiple houses, that’s just such a huge number of susceptible animals. How do you change that?” he said. “There’s no easy answer, not now… for the longest time you could have said, well maybe we should just decrease your barn density, change math, but now when the virus in the wild birds is so nasty, it’s really, really tough.”