Genetic changes accelerate spread and severity of epidemic H5N1 bird flu virus

Scientists at St. Jude Children’s Research Hospital show how the current H5N1 avian flu virus (bird flu) gained new genes and greater virulence as it spread westward. discovered. The researchers showed that this avian virus can cause severe brain infections in mammalian research models and is very different from previously related virus strains. Researchers genetically followed the virus as it spread across continents and settled in wild waterfowl populations to understand what made it so different. This research recently Nature Communications.

I have never seen a virus like this before. This particular her H5N1 influenza strain has been tracked by him for 24 years, and this ability to cause disease has not been confirmed in these wild bird populations. ”

Dr. Richard Webby, Corresponding Author, St. Jude Service for Infectious Diseases

When scientists tested a new avian influenza strain for its ability to cause disease in mammals by infecting a ferret model, they found it to be unexpectedly highly pathogenic.

“Some viruses are really nasty,” says Webby. “There is a huge amount of virus in the brains of infected animals, which is characteristic of what we have observed in these influenza strains. It’s not the first time we’ve seen H5 viruses.” But they’re probably some of the most virulent viruses we’ve tracked for 24 years. ”

Previous influenza viruses that caused severe illness in North America “burned out” the populations of their primary host birds, and epidemics quickly ended. This current strain was detected at high levels in diseased chickens, but is spreading to other species.

“This is no longer just a chicken virus,” Webby said. “Other birds and mammals are also being infected in the United States. For humans and other mammals, the risk of exposure is higher than it has been in North America. I’ve never been.” ”

Low risk to humans (so far)

This new strain of H5N1 flu has shown a higher ability to cause disease in mammals than previous viruses, but scientists have found it poses a lower risk to humans. This is because the virus appears to be well adapted for transmission between birds rather than between mammals.

“Overall, the risk to humans is still low,” Webby said. “However, that risk appears to be shifting, and these viruses are doing things that H5 viruses have never done before: they invade the continent’s wild bird populations, reassort, It has been maintained over time.” . Now there are many different types, and it is very troublesome. ”

Although the risk of spreading infection is low, the study suggests that humans should be cautious when interacting with wild animals.

“It’s going to take a lot of effort to catch this virus, but if you do get it, you’re very likely to get very sick,” Webby said. “People just need to be careful and remember that some wild animals may carry these highly pathogenic viruses.”

Widespread and increasing severity of genetic alterations

In the past, similar strains of influenza viruses have not caused as severe disease, nor have they spread widely within wild bird populations. The new strain did so much damage that scientists looked to see what was different. The group identified the direct ancestor of the current virus strain. This virus strain spread from Europe to the Americas after acquiring different versions of the viral protein neuraminidase. This new protein has increased the ability of the virus to be transmitted between birds. He then arrived on the east coast of Canada and headed for the United States.

As researchers studied the viruses further, they pinpointed exactly which virus was which. Unlike the previous ones -; caused the current epidemic. They found that after reaching North America, the virus changed rapidly again and became more virulent. It mixed with wild bird flu viruses from North America and exchanged some genes. This gene rearrangement he had two effects. For one, the virus seems to have adapted further to bird populations and infected many different species of birds. This included atypical hosts such as buzzards and eagles, which do not normally infect influenza. Second, the virus has acquired the ability to cause severe illness.

“What’s surprising is that just a few reassortment events in our model actually changed the ability of these viruses to cause disease,” said Webby. “And those events generated many different genotypes from that mix. Those viruses then spread and now have established themselves in North American wild bird populations.”

Webby and colleagues continue to monitor the ongoing global bird flu pandemic to assess the continuously evolving risks to both humans and birds.