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H7N9 potentially highly transmissible, virulent
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The influenza A(H7N9) virus has the potential to transmit easily among humans and cause a pandemic, new data suggest.
According to a report in The American Journal of Pathology, researchers from Rotterdam, the Netherlands, found that the virus attaches easily to the epithelium of the upper and lower respiratory tracts, which is a trait not previously observed with avian influenza viruses.
“Abundant virus attachment to the human upper respiratory tract correlates with efficient transmissibility among humans,” Thijs Kuiken, DVM, PHD, of the department of viroscience at Erasmus University Medical Centre, said in a press release. “Virus attachment to Clara cells in the bronchioles and pneumocytes and macrophages in the alveoli correlates with high virulence.”
Thijs Kuiken
Kuiken and colleagues used histochemical analysis to evaluate the attachment patterns of two genetically engineered emerging H7 viruses to human respiratory tract tissue. They compared these findings with attachment patterns seen with other human influenza viruses that are known to have high transmissibility but low virulence — seasonal H3N2 and pandemic H1N1 — and avian influenza viruses with low transmissibility but high virulence — H5N1 and H7N7.
Similar to other avian influenza viruses, H7N9 attached more strongly to the lower respiratory tract compared with the upper parts. In addition, the H7N9 viruses attached more abundantly to epithelial cells in the bronchioles and alveoli of the lung than other avian influenza viruses, and they attached to a broader range of cells. According to Kuiken, these attributes correlate with increased virulence compared with other human influenza viruses.
The researchers also found that there was more concentrated attachment of H7N9 viruses in the ciliated cells of the nasal concha, trachea and bronchi, which suggests potential for increased transmissibility.
“Our results indicate that just based on the pattern of virus attachment, the H7N9 currently emerging in China has the potential both to cause severe pulmonary disease and to be efficiently transmitted among humans,” Kuiken said. “However, the fact that the emerging virus has caused infection mainly in individual human cases suggests that it has not acquired all the necessary properties for efficient transmission among humans.”
Disclosure: Kuiken is a consultant for Viroclinics Biosciences.
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