New research suggests H5N1 bird flu can spread through the air

Penn State researchers have demonstrated airborne transmission of a new H5N1 virus strain in ferrets, marking a possible evolution of the virus to better infect mammals and possibly humans. The study, which reconstructed the virus from genetic sequences, emphasizes the importance of monitoring for mutations that could increase virulence and transmission. Credit:

New findings suggest that one strain of the H5N1 influenza virus has evolved only a minimal capacity for airborne transmission.

In March, the United States reported the first detection of highly pathogenic H5N1 avian influenza in dairy cattle, with the outbreak spreading to nine states by May. The method of transmission among cattle remains unclear. However, a study published in nature communication discovered that a similar H5N1 strain, subtype clade, which previously caused an outbreak in farmed mink in 2022, was capable of airborne transmission in a small group of ferrets.

This is the first time that a member of the H5N1 clade group of viruses has been shown to exhibit this ability. According to the Penn State researchers who led the study, the findings suggest that these viruses are evolving to infect mammals and potentially pose an increasing threat to humans.

“Although there is no evidence that the strain of H5N1 that is currently affecting dairy cattle is capable of spreading by air, our study shows that another member of this family of viruses is able to spread to a lesser extent. have evolved the ability to spread by wind,” said Troy Sutton, associate professor. Veterinary and Biomedical Sciences, Penn State, and corresponding author on the paper. “This discovery underscores the importance of continued surveillance to monitor the evolution of these viruses and their spread to other mammals, including humans.”

Virus assessment methodology

According to the researchers, while assessing a virusThe potential for airborne transmission in mammals may inform understanding of its potential risk to humans. Since virus samples could not be easily obtained after the outbreak in mink was controlled, the team reconstructed the virus using publicly available genetic sequences.

Next, the researchers evaluated the ability to transmit the virus in ferrets, which have respiratory tracts that are more similar to humans in susceptibility to viral infection and transmission, compared to other model organisms such as rats. The team measured both direct transmission of the virus by placing infected ferrets in cages with uninfected ferrets and indirect airborne transmission by placing infected and uninfected ferrets in cages that enable shared airspace but prevent physical contact. To assess the severity of the disease, the team examined the ferrets’ weight loss and signs of clinical disease.

Conclusion on virus transmission

The researchers found that the virus was transmitted by direct contact in 75% of exposed ferrets and by respiratory droplets in 37.5% of exposed ferrets after approximately nine days of contact. The team also found that the infectious dose of the virus was low, meaning that even small amounts of the virus cause infection.

Sutton said the mink strain of the virus has a mutation, called PB2 T271A. To test the effect of this mutation on viral transmission and disease severity, the team engineered the virus without the mutation and found that mortality and airborne transmission were reduced in ferrets infected with this version of the virus.

“These findings suggest that the PB2 T271A mutation is increasing viral replication of the virus, contributing to both virulence and transmission in ferrets,” Sutton said. “Understanding the role of this mutation means we can monitor for it or similar mutations arising in currently circulating strains of H5N1.”

implications for human health

Sutton said the ferrets the team used in their study had no pre-existing immunity to influenza, whereas most humans have been exposed to H1N1 and H3N2 seasonal influenza viruses.

“If humans are exposed to another H5N1 variant, this exposure will likely provide some degree of cross-protection against H5N1,” he said.

Additionally, he said the transmission rate observed by the team in the mink virus is lower than that of pandemic influenza viruses.

“Pandemic influenza viruses typically spread by airborne route to 75% to 100% of contacts within three to five days, whereas the mink virus we studied spread to less than 40% of contacts after nine days,” Sutton said. spreads out.” “The transmission observed in our study is indicative of increased pandemic potential relative to previously characterized strains of H5N1; However, mink virus does not exhibit the same properties as pandemic strains. The H5N1 strain affecting cattle has not caused severe disease in cattle or humans, but the longer the virus circulates, and the more humans are exposed to it, the more likely it will be to infect humans. Will develop for.

References: Katherine H. Restori, Kayla M. Scepter, Cassandra J. Field, Devanshi R. “Risk assessment of highly pathogenic H5N1 influenza viruses from mink” by Patel, David VanInsberg, Vedhika Raghunathan, Ennis C. Loewen, and Troy C. Sutton, 15 May 2024, nature communication,
DOI: 10.1038/s41467-024-48475-y

This research was done by Penn State’s Eva J. The test was conducted at the Pell Advanced Biological Laboratory, a high-containment biosafety level 3 advanced laboratory that is routinely inspected by the Centers for Disease Control and Prevention and the United States Department of Agriculture.

Other Penn State authors on the paper include Katherine Restori, assistant research professor in veterinary and biomedical sciences, as well as Kayla Scepter, Cassandra Field and Devanshi Patel, all graduate students in veterinary and biomedical sciences. David VanInsberg, Postdoctoral Fellow; Vedhika Raghunathan, graduate student; and Ennis Loewen, professor of microbiology and immunology at Emory University, are also authors of the paper.

National Institutes of Health And the National Institute of Food and Agriculture supported this research.


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