Wild fowl caused Lincoln duck farm outbreak
It was through contact with wild fowl that an outbreak of avian influenza occurred on a Lincoln duck farm this summer.
But wild birds, including migratory waterfowl, have played a much larger role in the spread of the virus into Europe and North America.
That was the conclusion reached by a group of scientists from across the globe, who recently published their findings focused on avian influenza and the impact of migratory birds.
As a result, farmers are being reminded of the importance of maintaining strict biosecurity measures at all times on their poultry farms, said Dr. John Pasick, veterinary national authority with the Canadian Food Inspection Agency.
Pasick, involved in two recent scientific papers regarding the spread of avian flu, confirmed it was a “wild bird introduction” that was believed to have caused the early-July outbreak that saw a King Street farm placed under quarantine until mid-August.
As a result, 14,000 ducks on the property were euthanized to prevent spread of the disease.
The low pathogenic H5 strain discovered on the farm causes only mild illness in birds, but is capable of mutating to a high pathogenic form, which can be dangerous not only for other types of animals, but also for humans.
“The sequences for all of the genes of that virus were … all of wild bird origin. North American wild bird origin,” Pasick said. That differs from the exotic Eurasian origin that caused a highly pathogenic outbreak in British Columbia in 2014 and a large outbreak in the U.S. in 2015.
Those outbreaks were at the centre of Pasick’s recent research, as he worked with other scientists to track movement of H5 avian influenza over time.
It was determined migratory birds were at the centre of the spread from China, where it first appeared in 1996, to North America.
While wild birds were suspected of being involved in the spread at that time, some scientists suspected illegal movement of poultry may have also contributed, Pasick said.
“There was some debate as to what roles each played.”
Research has since determined both the B.C. and U.S. outbreaks in recent years trace back to the original 1996 virus that arose in China.
It’s believed those recent cases occurred after wild birds carried the virus from South Korea to breeding grounds in Siberia, before spreading it westward into Europe and eastward via overlapping migratory pathways across the Bering Strait to Alaska and down the Pacific Flyway to B.C., he said.
“There’s pretty good evidence suggesting this was the way the virus was introduced to North America.”
At one time it was thought birds carrying H5 influenza would be too sick to migrate and wouldn’t be able to spread the disease over long distances.
But the recent research changes that thought, Pasick said.
There are three varieties of ducks suspected of bringing the virus to North America: the northern pintail, American green-winged teal and the common teal.
“Both have their breeding grounds in Alaska. Some even cross over into Siberia,” Pasick said. “They are long-distance migrants.”
As birds migrate, they tend to assemble in certain areas in large concentrations, which can result in the exchange of viruses.
With migration season underway, there’s an added risk of influenza being introduced to poultry barns, he said, urging farmers to take precautions to prevent breaches from occurring.
But maintaining strict biosecurity “is maybe easier said than done,” he said.
“All it takes is one slip. I think biosecurity is like a chain, and the virus can sometimes find the weakest link in the chain to get in.”
While it’s known the H5 and H7 viruses exist among wild fowl, they are present only in their low-pathogenic form, Pasick said.
“It’s only when they get introduced to domestic poultry that on occasion they can evolve into a high-pathogenic form.”
With research now indicating migratory birds are responsible in part for the spread of the disease, Pasick said focus in the field will shift.
The next step will be looking in more detail at how biosecurity can be breached, how the high-pathogenic strains are maintained in wild bird populations, what causes some viruses to evolve into a high-pathogenic form, while others do not, and what characteristics are involved in making that transition.
“Those are some of the questions we’re going to hopefully be focusing on.”