The resurgence of H7N9 in recent months has pushed the death toll from the virus up past 70, but so far the bird flu has been mainly limited to bird-to-human transmission on mainland China. However, the seasonal circulation of H7N9 is putting it into contact with other flu viruses, and researchers fear a more contagious, virulent strain could result.
Writing in the journal Eurosurveillance, researchers at the Shanghai Public Health Clinical Center and Institutes of Biomedical Sciences describe how H7N9 is interacting with H9N2. Analysis of circulating flu viruses revealed three new strains of H7N9 that incorporate genetic material from H9N2. Such reassortment is fundamental to the evolution of flu viruses and can have little impact on how they affect humans. Eventually, though, a mutation with the feared combination of human-to-human transmissibility and increased pathogenicity could emerge.
"Each new strain could be one that is better genetically equipped to transmit from person to person. Without contemporary sequence analysis, such a strain could emerge from among the 'noise' of human infection by less efficient strains, to begin spreading rapidly and with pandemic potential," University of Queensland associate professor Ian Mackay told Bloomberg. The Eurosurveillance paper focuses on mutations to the PB1 gene, but experts interviewed by Bloomberg were unclear why changes to this material might affect pandemic risk.
Sequencing studies looking at other genes are needed to fully gauge how H7N9 is evolving. For now the available data suggests H7N9 has yet to become the virus health authorities fear. "The epidemiological data doesn't support the premise that we have got either increased transmissibility or increased pathogenicity with this current outbreak versus the one in early 2013," Ian Barr, deputy director of the Melbourne WHO Collaborating Centre, said.