Abstract
The cocirculation of H5N1 and H9N2 avian influenza viruses in birds in Egypt provides reassortment opportunities between these two viruses. However, little is known about the emergence potential of reassortants derived from Egyptian H5N1 and H9N2 viruses and about the biological properties of such reassortants. To evaluate the potential public health risk of reassortants of these viruses, we used reverse genetics to generate the 63 possible reassortants derived from contemporary Egyptian H5N1 and H9N2 viruses, containing the H5N1 surface gene segments and combinations of the H5N1 and H9N2 internal gene segments, and analyzed their genetic compatibility, replication ability, and virulence in mice. Genes in the reassortants showed remarkably high compatibility. The replication of most reassortants was higher than the parental H5N1 virus in human cells. Six reassortants were thought to emerge in birds under neutral or positive selective pressure, and four of them had higher pathogenicity in vivo than the parental H5N1 and H9N2 viruses. Our results indicated that H5N1-H9N2 reassortants could be transmitted efficiently to mammals with significant public health risk if they emerge in Egypt, although the viruses might not emerge frequently in birds.IMPORTANCE Close interaction between avian influenza (AI) viruses and humans in Egypt appears to have resulted in many of the worldwide cases of human infections by both H5N1 and H9N2 AI viruses. Egypt is regarded as a hot spot of AI virus evolution. Although no natural reassortant of H5N1 and H9N2 AI viruses has been reported so far, their cocirculation in Egypt may allow emergence of reassortants that may present a significant public health risk. Using reverse genetics, we report here the first comprehensive data showing that H5N1-N9N2 reassortants have fairly high genetic compatibility and possibly higher pathogenicity in mammals, including humans, than the parental viruses. Our results provide insight into the emergence potential of avian H5N1-H9N2 reassortants that may pose a high public health risk.
Highlights
The cocirculation of H5N1 and H9N2 avian influenza viruses in birds in Egypt provides reassortment opportunities between these two viruses
As reported by others [8], phylogenetic analyses of the eight gene segments of these viruses indicated cocirculation of H5N1 and H9N2 viruses in Egypt and showed that A/chicken/Egypt/CL69/2013 (H5N1) and A/chicken/ Egypt/CL42/2013 (H9N2) are representative strains of contemporary H5N1 clade 2.2.1.2 and H9N2 G1-B influenza viruses isolated in Egypt
Receptor binding assays showed that both CL69 and CL42 have acquired increased binding affinity to ␣2,6 Sia compared to ancestral clade 2.2.1 and classical H9N2 strains, respectively (Fig. 1A and B), implying an increased avian-to-human infection potential of both subtypes in Egypt
Summary
The cocirculation of H5N1 and H9N2 avian influenza viruses in birds in Egypt provides reassortment opportunities between these two viruses. Our results indicated that H5N1-H9N2 reassortants could be transmitted efficiently to mammals with significant public health risk if they emerge in Egypt, the viruses might not emerge frequently in birds. IMPORTANCE Close interaction between avian influenza (AI) viruses and humans in Egypt appears to have resulted in many of the worldwide cases of human infections by both H5N1 and H9N2 AI viruses. We report here the first comprehensive data showing that H5N1-N9N2 reassortants have fairly high genetic compatibility and possibly higher pathogenicity in mammals, including humans, than the parental viruses. Egypt has unexpectedly had more human H5N1 infections than any other country, with about 66.2% of the cases worldwide since 2009 (as of 2 March 2018, according to the WHO) This implied appreciably closer interaction between H5N1 viruses and humans in Egypt than in other geographic areas and/or virological properties that are not yet understood [6]. A seroepidemiological study has indicated that human H9N2 infections are more prevalent in Egypt than has been reported [9]
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