St. Jude Children’s Research Hospital scientists discovered how the current epizootic H5N1 avian influenza virus (bird flu) gained new genes and greater virulence as it spread west. Researchers showed that the avian virus could severely infect the brains of mammalian research models, a notable departure from previous related strains of the virus. The researchers genetically traced the virus’ expansion across the continent and its establishment in wild waterfowl populations to understand what makes it so different. The study was recently published in Nature Communications.
“We haven’t seen a virus quite like this one,” said corresponding author Richard Webby, Ph.D., St. Jude Department of Infectious Diseases. “In 24 years of tracing this particular H5N1 flu lineage, we haven’t seen this ability to cause disease but also be maintained in these wild bird populations.”
When the scientists tested the newer avian flu strains for their ability to cause disease in mammals by infecting a ferret model, they found an unexpectedly high amount of pathogenicity.
“Some of these are really nasty viruses,” Webby said. “There’s a huge amount of the virus in the brain of infected animals. That’s the hallmark of what we saw with these flu strains — increased pathogenicity associated with high virus load in the brain. That’s not the first time we’ve seen H5 viruses in the brain, but these are probably some of the most virulent we’ve looked at over 24 years of following these viruses.”
Previous influenza viruses that caused severe disease in North America “burned out” in their main host bird population, and the outbreaks ended quickly. This current strain was detected at high levels in sick chickens but has expanded into other species.
“This is not just a chicken virus now,” Webby said. “It’s also infecting other avian and mammal species in the U.S. It’s a higher exposure risk for humans and other mammals than we’ve ever had in North America. We’ve never really been exposed to this level of circulation of these highly pathogenic flu viruses.”