Avian Influenza H7N9 Virus Adaptation to Human Hosts.

Swan Tan,Nik Elena Nik Mohamed,Muhammad Farhan Sjaugi,Siew Chinn Fong,Li Chuin Chong,Hadia Syahirah Abd Raman,Joseph Thomas August,Asif M Khan

doi:10.3390/v13050871

Swan Tan, Nik Elena Nik Mohamed + Show 6 more

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https://doi.org/10.3390/v13050871

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Abstract

Avian influenza virus A (H7N9), after circulating in avian hosts for decades, was identified as a human pathogen in 2013. Herein, amino acid substitutions possibly essential for human adaptation were identified by comparing the 4706 aligned overlapping nonamer position sequences (1–9, 2–10, etc.) of the reported 2014 and 2017 avian and human H7N9 datasets. The initial set of virus sequences (as of year 2014) exhibited a total of 109 avian-to-human (A2H) signature amino acid substitutions. Each represented the most prevalent substitution at a given avian virus nonamer position that was selectively adapted as the corresponding index (most prevalent sequence) of the human viruses. The majority of these avian substitutions were long-standing in the evolution of H7N9, and only 17 were first detected in 2013 as possibly essential for the initial human adaptation. Strikingly, continued evolution of the avian H7N9 virus has resulted in avian and human protein sequences that are almost identical. This rapid and continued adaptation of the avian H7N9 virus to the human host, with near identity of the avian and human viruses, is associated with increased human infection and a predicted greater risk of human-to-human transmission.

Highlights

Influenza A viruses belong to the Orthomyxoviridae family and circulate among aquatic wildfowl, which is their natural reservoir [1,2]
With many additional mutations of the other virus proteins that are selected by fitness in a given host [5], influenza viruses exist as a vast number of different strains that infect multiple bird and several mammalian species, including Homo sapiens
The analyses identified amino acid substitutions of nonamer sequences that distinguished the H7N9 strains recovered from avian and the newly reported human hosts in 2014, and it assessed the continued evolution of the avian and human viruses, as reported in 2017

Summary

Introduction

Influenza A viruses belong to the Orthomyxoviridae family and circulate among aquatic wildfowl, which is their natural reservoir [1,2]. They mutate very rapidly as quasispecies [3], with over 100 subtypes based on different combinations of the external proteins, hemagglutinin (HA) and neuraminidase (NA) [4]. The initial H1N1 Spanish flu of 1918/1919 claimed over 40 million lives [2,7,8,9] Other subtypes, such as H5N6, H6N1, H7N2, H7N3, H7N7, H9N2, H10N7 and H10N8, are capable of causing human infection as well [10]. The most recent human adapted subtypes, H5N1 and H7N9, despite the lack of H2H spread, have infected hundreds of people [11]

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