Via STAT, Helen Branswell brings back memories: What happened to bird flu? How a threat to human health faded from view. Excerpt from a very good article:
Just over a dozen years ago, a bird flu virus known as H5N1 was charting a destructive course through Asia, North Africa, and the Middle East, ravaging poultry in apocryphal numbers and killing 6 in 10 humans known to have contracted it.
The overall human death toll was low — in the hundreds — but scientists and government officials feared that the virus could ignite a human pandemic reminiscent of the catastrophic 1918 Spanish flu. Emergency plans were drafted, experimental H5N1 vaccines were created and tested, antiviral drugs were stockpiled.
And then … nothing happened.
The virus continued to kill chickens and to occasionally infect and sometimes kill people. But as the years passed, the number of human H5N1 cases subsided. There has not been a single H5N1 human infection detected since February 2017.
This is the good news. The bad news is that the situation could change in an instant. Related: How live animal markets create a perfect storm for bird flu
“We don’t know how the story’s going to end,” warned Nancy Cox, who retired from the Centers for Disease Control and Prevention in late 2014 after leading its influenza operations for more than two decades.
It’s not just H5N1 that has dissipated. The virus’s nearly-as-scary cousin, H7N9, emerged in China in 2013 and sickened more than 1,500 people in China over five years, killing roughly 40 percent of them.
But after an extraordinary surge of cases — 766 — in early 2017, there were a mere three infections recorded in 2018. So far in 2019 there have been none.
Although there are ways to make sense of H7N9’s decline, no one knows precisely why H5N1 has faded from view.
“There are things that occur with influenza that don’t quite add up completely,” Cox admitted.
Scientists do know the H5N1 viruses have mutated in ways that may be important to their ability to interact with people. Several years ago, these viruses effectively splintered, with some dumping their N1 neuraminidase — a gene that produces a key protein found on the surface of flu viruses — and replacing it with another. The process is called reassortment, and, in this case, it resulted in the emergence of a lot of new pairings over a fairly short period of time.
The most common and most dangerous viruses to emerge — for birds at least — have been H5N6 and H5N8 viruses. Both are highly pathogenic, meaning they kill domestic poultry.
“The H5N1 virus has not gone away. It’s just changed into different versions of itself,” explained influenza expert Malik Peiris, a professor of virology at the University of Hong Kong. “We don’t know how the story’s going to end.”
Peiris suggested it might be a mistake to see the evolution of the virus as nothing but a positive development.
“It is good news, the fact that overall the H5N1 problems have reduced,” he said. “But you know, you can look at it the other way around. So now we have two high pathogenic [H5] viruses kicking around.”
