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A recent bird flu death in Washington state is a reminder that H5 influenza is still circulating in birds in the United States, as seasonal flu cases begin to rise. That increases the bird flu threat to humans.
Dr. Jason Bowling, professor and interim chief of the Division of Infectious Diseases at UT Health San Antonio, and director of hospital epidemiology at University Health, said public health experts become concerned when avian flu is circulating in birds at the same time seasonal flu is circulating in humans.
"We always worry when you see avian flu in a person," Bowling said. "It can run basically undercover because there's so much actual flu going out there."
The person who died from bird flu in late November picked it up from their backyard birds, according to that state's health department. No one else was infected. Avian flu, so far, hasn't evolved a strain that can pass easily from human to human. But Bowling explained that when avian flu is circulating in birds at the same time seasonal flu is circulating in humans, the risk rises for the emergence of an avian flu strain that is contagious between humans.
That could happen if someone picks up avian flu from a bird and gets seasonal flu from someone in their community at about the same time; those viruses can start swapping segments in a process called reassortment.
"So they have two infections at the same time, which is not uncommon," Bowling said. "And those segments could reassort and then create an entirely new virus. And that's what we saw in 2009 when we had that huge pandemic."
Bowling is talking about the 2009 swine flu pandemic, which resulted in up to half a million deaths worldwide. It was the result of a triple reassortment of swine, avian, and human flu viruses. Bowling stressed, however, that this doesn't happen every time someone is infected with more than one flu virus.
"It may take multiple times for it to happen before it reassorts like that," Bowing said. "But there's a potential each and every time. And the more cases that you have, the higher the risk that you're going to have one that takes off and is able to transmit from person to person and cause significant issues."
During an active flu season, one of those issues is that doctors might not immediately recognize the evolution. "It could potentially start spreading from person to person, and it would be harder to detect because of the huge volume of flu strains we normally see," Bowling explained, "Which is why we need surveillance to look for more avian flu. We need good public health infrastructure. And we also need people to take precautions to keep themselves from getting sick."
Precautions include getting a flu vaccine, if you haven't already. Bowling said even though there's a slight mismatch between this year's vaccine and the dominant circulating strain, the shot does offer some protection against severe illness and flu-related complications. If you get one now, your immune system will be well-trained to fight the flu by the time the holiday season shifts into high gear. Those who are sick and may be contagious should stay home.
" Even if they're not at high risk for severe illness themselves, they could potentially be an intermediary host for a couple of strains of flu, or they could get somebody else who is at high-risk sick," Bowling said.
The bird flu death in Washington was the first recorded human death from the H5N5 strain of bird flu in the world. It was the second avian flu death in the United States this year. Someone in Louisiana died from H5N1 in January.
As for seasonal flu, there was another bump in seasonal flu cases across the country during the week ending the Saturday before Thanksgiving, the most recent week reported by the Centers for Disease Control, with H3N2 flu taking the lead by a wide margin.
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