Abstract
The novel H7N9 influenza virus, which has caused severe disease in humans in China, is a reassortant with surface genes derived from influenza viruses in wild birds. This highlights the importance of monitoring influenza viruses in these hosts. However, surveillance of influenza virus in wild birds remains very limited in China. In this study, we isolated four H4N6 avian influenza viruses (AIVs) from mallard ducks in Beijing Wetland Park, which is located on the East Asia–Australasia migratory flyway. The gene segments of these Chinese H4N6 viruses were closest to AIVs in wild birds from Mongolia or the Republic of Georgia, indicating the interregional AIV gene flow among these countries. All of our isolates belonged to a novel genotype that was different from other H4N6 viruses isolated in China. We further evaluated the virulence and transmission of two representative H4N6 strains in mammalian models. We found that both of these H4N6 viruses replicated efficiently in mice without adaptation. Additionally, these two strains had a 100% transmission rate in guinea pigs via direct contact, but they had not acquired respiratory droplet transmissibility. These results reveal the potential threat to human health of H4N6 viruses in migratory birds and the need for enhanced surveillance of AIVs in wild birds.
Highlights
Influenza viruses circulating in animals are novel to the human immune system; these viruses pose a potential threat to public health once they are transmitted to humans
Influenza pandemics have been caused by animal influenza viruses or avian influenza viruses reassorting with human influenza viruses [1,2]
A novel H7N9 influenza virus caused a total of 1364 laboratory-confirmed cases of influenza, with a nearly 33% case-fatality rate reported to the World Health Organization since its first detection in February 2013 in China [3]
Summary
Influenza viruses circulating in animals are novel to the human immune system; these viruses pose a potential threat to public health once they are transmitted to humans. Animal influenza viruses can even cause pandemics in a human population once they acquire efficient transmissibility between people. Influenza pandemics have been caused by animal influenza viruses (as in the 1918 and 2009 pandemics) or avian influenza viruses reassorting with human influenza viruses (pandemics in 1968 and 1957) [1,2]. A novel H7N9 influenza virus caused a total of 1364 laboratory-confirmed cases of influenza, with a nearly 33% case-fatality rate reported to the World Health Organization since its first detection in February 2013 in China [3]. Genetic analyses have found that this virus is a reassortant whose surface genes are directly derived from H7 and N9 subtypes of the wild bird viral
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