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High Alert: H3N8 Avian Influenza Virus Shows Potential for Airborne Human Transmission

Recent cases of human infection with the H3N8 avian influenza virus in China have raised concerns, particularly after one patient succumbed to pneumonia due to the infection. A new study, published in the respected journal Cell, has unveiled alarming findings. The H3N8 virus isolated from humans demonstrates the ability to transmit through the air among ferrets, marking a significant step towards potential inter-human transmission. Close vigilance is now imperative.

Using laboratory-cultivated human respiratory organoid models, researchers delved into the virus’s infectivity in humans. Results unveiled its capability to infect and replicate in human bronchial and lung epithelial cells. Significantly, the human-isolated strain exhibited higher infectivity compared to the avian-origin variant, leading to severe respiratory complications and viral encephalitis.

While the avian-origin H3N8 virus could infect ferrets, it struggled with efficient transmission among them. Conversely, the human-isolated strain demonstrated heightened transmissibility, even generating virus-laden aerosols in the air. This indicates the virus’s adaptability to mammalian hosts, culminating in infection and illness.

Deep sequencing analysis revealed the virus’s ability to rapidly undergo genetic adjustments and accumulate adaptive mutations post-transmission among ferrets. Notably, it could also swiftly mutate within human hosts, suggesting a potential for human-to-human transmission.

Currently, the H3N8 avian influenza virus lacks the capacity for person-to-person transmission due to the inadequate acid stability of its hemagglutinin (HA) protein. The mildly acidic environment of the upper respiratory tract in humans poses a challenge for the virus’s respiratory cell infection. Researchers posit that mutations enhancing the HA protein’s stability in acidic conditions could substantially elevate the risk of a widespread outbreak.

In a concerning revelation, a study found that the trivalent influenza vaccine, administered to 30 individuals, proved ineffective against the novel H3N8 virus. This indicates a critical gap in vaccine coverage against this emerging strain.

Given the continued high detection rate of the H3N8 avian influenza virus in Chinese poultry, proactive source control is imperative. This involves vigilant monitoring of H3 avian influenza prevalence in poultry populations to gain crucial insights into its spread.

As China experienced three human H3N8 virus cases between 2022 and 2023, and with the virus showing signs of increased adaptability, strategic measures are vital. These include enhanced surveillance, robust research, and proactive vaccine development to mitigate the risk of a potential large-scale outbreak.

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