Study shows ‘not surprising’ fatal spread of avian flu in ferrets

CIDRAP

Late last week the Centers for Disease Control and Prevention (CDC) published a study showing that the current strain of H5N1 (A/Texas/37/2024) avian flu was fatal in six ferrets used as part of an experimental infection study. The findings caused waves across the country, as ferrets are frequently used as an animal model stand-in for people. 

But Michael T. Osterholm, PhD, MPH, who directs the University of Minnesota’s Center for Infectious Disease Research and Policy (CIDRAP), publisher of CIDRAP News, was not surprised by the findings. 

No evidence to support serious illness in people

Osterholm said H5 viruses like H5N1 have historically been fatal to ferrets, and, moreover, the ferrets used in the study were immune-naive animals with no previous exposure to any influenza viruses. 

“Previous H5 isolates have also been put into the ferret model and found similar results,” said Osterholm. “I would have been surprised had it not done that [killed the ferrets.] This doesn’t minimize what is happening with H5, but there is no evidence to date that would support serious illness in humans.”

Osterholm said researchers are still trying to understand the wider implications of the H5 cases. 

In the CDC study, the authors noted that the H5N1 virus, which was taken from the human case-patient in Texas, spread efficiently between ferrets only through direct contact but not via respiratory droplets. 

“This is different from what is seen with seasonal flu, which infects 100% of ferrets via respiratory droplets,” the CDC said. “These findings are not surprising and do not change CDC’s risk assessment for most people, which is low.”