(Bloomberg) -- A pig tested positive for the H5N1 bird flu for the first time in the US, government officials said, a feared development that could help the virus further evolve and put humans at risk.
The infection was confirmed in a pig kept on a backyard farm in Crook County, Oregon, the US Department of Agriculture said Wednesday. US health officials have worried that the virus, already spreading in birds and cattle, would jump into swine.
Pigs have long been considered mixing vessels where flu viruses from humans and birds can exchange genes. The concern is that such hybrid, or reassortant, pathogens can emerge with characteristics that allow them to infect humans more easily.
“Of all the hosts that we know of influenza, pigs are the one that can be a bridge to humans,” Richard Webby, a flu specialist at St. Jude Children’s Research Hospital in Memphis, said in an interview.
So far this year, 35 humans have contracted the virus, most of whom worked on farms with infected animals. While those infections have been mild for the most part, bird flu has been known to be lethal to humans in many cases.
The owners of the backyard farm alerted officials when ducks and geese started getting sick and dying.
The infection was caused by the strain that’s been circulating in wild birds, said Ryan Scholz, state veterinarian for the Oregon Department of Agriculture. There’s no sign it’s been passed on to any humans, said Dean Sidelinger, Oregon’s state health officer.
Quietly Lurking
“While there is no reason to panic, we know from past experience how bad pandemic influenza is and in particular, H5N1 has been quietly lurking for more than a decade,” said Michael Kinch, an immunology expert who’s chief innovation officer at Stony Brook University in New York.
One of five pigs on the farm has been confirmed with H5N1, with evidence of infection throughout its body. The animal didn’t show any sign of illness, the USDA said in a statement. Two teacup mini pigs were also swabbed, and there was an indication that the virus was present in the nose or mouth of at least one, officials said.
Tests are still underway for the others.
Laboratory analyses haven’t turned up worrisome signs of genetic changes that would make the virus more virulent or spread more easily, Sidelinger said. The possibility is still a concern, he said.
“We do worry about changes in this virus,” he said. “A pig could potentially be co-infected, and then we could see some intermingling of those viruses, which is why additional studies are being done.”
Vigilance Needed
The pig’s lack of symptoms increases the need for vigilance, according to Benjamin Anderson, an assistant professor of environmental and global health at the University of Florida.
“Most of our testing for H5N1 in farm settings to date has only occurred due to clinical outbreaks,” he said in an email. If the virus is causing little or no illness in pigs, “then we may not catch it without regular ongoing testing.”
The USDA and the Oregon Department of Health tested the pigs after animals on the farm — such as livestock and poultry — contracted H5N1. The animals shared water sources, housing and equipment, and “this combination has enabled transmission between species,” the USDA said.
All five pigs were euthanized. The farm has been quarantined to prevent further spread of H5N1, the USDA said. The department sequenced the virus from poultry on the farm and shared the results with the Centers for Disease Control and Prevention. Neither agency found genetic changes that would suggest that it’s more transmissible to humans.
“Based on available information, the risk to the general public remains low,” the CDC said.
Pork Safety
The USDA added that there is “no concern about the safety of the nation’s pork supply as a result of this finding.”
Properly handled and cooked pork products remain safe for consumption, Bryan Humphreys, chief executive officer of the National Pork Producers Council, said in a statement. The industry “remains committed to safeguarding food safety and human and animal health,” he said.
The US bird flu outbreak has swept through poultry in 48 states, affecting dairy herds in 14 states, according to the CDC, which is continuing to investigate the outbreak with the USDA and state and local officials.
--With assistance from Michael Hirtzer and Jessica Nix.
(Adds comment from the CDC in the 16th, 17th and 20th paragraphs.)
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