Study shows 'not surprising' fatal spread of avian flu in ferrets


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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."

These findings are not surprising and do not change CDC's risk assessment for most people, which is low.

The CDC said the results do reinforce the need for people who work with infected animals to take precautions.

Household spread in pet ferrets

In related news, a study out of Poland described the first documented cases of natural H5N1 cases in five pet ferrets, which occurred at the same time the country saw an uptick of H5 cases in cats in 2023. 

The three juvenile pet ferret became sick, and one of them died, but all tested positive for the virus, including the adult animals, which exhibited no or minimal symptoms. 

"This outbreak suggests the possibility of asymptomatic A/H5N1 virus shedding by ferrets, highlighting their zoonotic potential and the advisability of excluding fresh or frozen poultry from their diet to reduce the A/H5N1 virus transmission risks," the authors wrote.

Wyoming becomes 12th state with infected dairy cows

Officials in Wyoming have confirmed that a dairy herd in that state is now infected with avian flu, the 12th affected state in the country. 

The detection was first identified in samples received by the Wyoming State Veterinary Laboratory and was confirmed by the US Department of Agriculture (USDA).

"The Wyoming Livestock Board encourages all dairy producers to closely monitor their herd and contact their herd veterinarian immediately if their cattle appear symptomatic,” said State Veterinarian Hallie Hasel, DVM. "The primary concern with this diagnosis is on-dairy production losses, as the disease has been associated with decreased milk production. The risk to cattle is minimal and the risk to human health remains very low."

In Iowa, which confirmed high-path avian flu in dairy cattle last week, officials from the Iowa Department of Agriculture and Land Stewardship are requesting resources from the USDA and announcing additional response measures, including providing compensation for culled dairy cattle at a fair market value and compensation for lost milk production at a minimum of 90% of fair market value. 

International avian flu developments 

In global developments:

  • Tomorrow the European Union will sign a contract with vaccine manufacturer CSL Seqirus for 665,000 doses of avian influenza vaccine, with an option for a further 40 million vaccines for a maximum of 4 years, according to Reuters. The doses are meant to be used as prevention by poultry farm workers and veterinarians.
  • The World Health Organization at the end of last week issued a Disease Outbreak News notice on the H5N1 case in Australia first reported more than 2 weeks ago. It noted that the patient is a 2.5-year-old girl who had been hospitalized for 2.5 weeks before recovering.
  • Avian flu has now been confirmed on five farms in Victoria, Australia, with the latest detection involving the H7N3 strain, and one supermarket chain is limiting egg sales.
  • Countries reporting new high-path avian flu outbreaks in wild birds or poultry include Latvia, Norway, and the United Kingdom.


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