Penn State researchers have demonstrated airborne transmission of a new strain of the H5N1 virus in ferrets, marking a potential evolution of the virus to better infect mammals and possibly humans. The study, which reconstructed the virus from genetic sequences, highlights the importance of monitoring mutations that could increase virulence and transmission. Credit: SciTechDaily.com
New findings show that one strain of the H5N1 influenza virus has developed only minimal ability for airborne transmission.
In March, the United States reported its first detection of highly pathogenic H5N1 avian influenza in dairy cattle, with outbreaks spreading to nine states by May. The method of transmission among cattle remains unclear. However, a study published in Natural communications found that a similar H5N1 strain, subtype clade 2.3.4.4b, which previously caused an outbreak in farmed mink in 2022, was capable of airborne transmission to a small group of ferrets.
This is the first time that a member of the H5N1 virus group of clade 2.3.4.4b has exhibited this ability. According to the Penn State researchers who led the study, the findings suggest that these viruses are evolving to infect mammals and pose a potentially increased risk to humans.
“While there is no evidence that the H5N1 strain currently affecting dairy cattle is capable of airborne transmission, our study suggests that another member of this virus family has developed some degree of transmissibility by air,” said Troy Sutton, associate professor of veterinary and biomedical sciences, Penn State, and corresponding author of the paper. “This discovery highlights the importance of continued surveillance to track the evolution of these viruses and their spread to other mammals, including humans. »
Virus assessment methodology
According to the researchers, the evaluation of a virusThe potential for airborne transmission in mammals could inform understanding of its potential risk to humans. Since it was not possible to easily obtain virus samples once the mink outbreak was contained, the team reconstructed the virus using publicly available genetic sequences.
Next, the researchers assessed the virus’s ability to transmit in ferrets, whose respiratory tracts are more similar to those of humans in terms of susceptibility to viral infection and transmission than other model organisms, such as ferrets. mouse. 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 allowing shared airspace but preventing any physical contact. To assess the severity of the disease, the team looked at the ferrets’ weight loss and clinical signs of the disease.
Results on virus transmission
Researchers found that the virus was transmitted by direct contact to 75% of exposed ferrets and by respiratory droplets to 37.5% of exposed ferrets after about nine days of exposure. The team also found that the virus had a low infectious dose, meaning that even small amounts of virus caused infection.
Sutton noted that the mink strain of the virus contained a mutation, called PB2 T271A. To test the influence of this mutation on viral transmission and disease severity, the team engineered the virus without the mutation and found that mortality and airborne transmission in ferrets infected with this version of the virus were reduced. .
“These results suggest that the PB2 T271A mutation enhances viral replication of the virus, contributing to both virulence and transmission in ferrets,” Sutton said. “Understanding the role this mutation plays means we can monitor it or the appearance of similar mutations in currently circulating H5N1 strains.”
Implications for human health
Sutton added that the ferrets the team used in their studies had no pre-existing immunity to influenza, while the majority of humans have been exposed to the seasonal H1N1 and H3N2 influenza viruses.
“This exposure would likely provide some degree of cross-protection against H5N1 if humans were exposed to another H5N1 variant,” he said.
Additionally, he said the transmission rate the team observed in the mink virus is lower than that typical of pandemic flu viruses.
“Pandemic influenza viruses are generally transmitted by air to 75 to 100% of contacts within three to five days, whereas the mink virus we studied was transmitted to less than 40% of contacts after nine days,” Sutton said. “The transmission observed in our studies indicates increased pandemic potential compared to previously characterized H5N1 strains; however, the mink virus does not exhibit the same attributes as pandemic strains. The H5N1 strain affecting cattle has also not caused serious illness in cattle or humans, but the longer the virus circulates and the more humans are exposed to it, the greater the chance it will evolve to infect cattle. humans.
Reference: “Risk assessment of a highly pathogenic H5N1 influenza virus from mink” by Katherine H. Restori, Kayla M. Septer, Cassandra J. Field, Devanshi R. Patel, David VanInsberghe, Vedhika Raghunathan, Anice C. Lowen and Troy C. Sutton, May 15, 2024, Natural communications.
DOI: 10.1038/s41467-024-48475-y
This research was conducted at Penn State’s Eva J. Pell Advanced Biological Laboratory, an enhanced, high-containment Biosafety Level 3 laboratory that is regularly inspected by the Centers for Disease Control and Prevention and the United States Department of Agriculture. United.
Other authors of the Penn State paper include Katherine Restori, research assistant professor of veterinary and biomedical sciences, as well as Kayla Septer, Cassandra Field and Devanshi Patel, all graduate students in veterinary and biomedical sciences. David VanInsberghe, postdoctoral fellow; Vedhika Raghunathan, graduate student; and Anice Lowen, professor of microbiology and immunology, all at Emory University, are also authors of the paper.
THE National Institutes of Health and the National Institute of Food and Agriculture supported this research.
News Source : scitechdaily.com
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