[Source: Journal of Virology, full page: (LINK). Abstract, edited.]


Analysis of recombinant H7N9 wild type and mutant viruses in pigs shows Q226L in HA is important for transmission

Qinfang Liu a, Bin Zhou b, Wenjun Ma a, Bhupinder Bawa a, Jingjiao Ma a, Wei Wang b, Yuekun Lang a, Young Lyoo a, Rebecca A. Halpin b, Xudong Lin b, Timothy B. Stockwell b, Richard Webby c, David E. Wentworth b† and Juergen A. Richt a†

Author Affiliations: Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS, 66506, USA<SUP>a </SUP>Virology, J. Craig Venter Institute, Rockville, MD 20850, USA<SUP>b </SUP>Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105, USA<SUP>c</SUP>
<SUP></SUP>
Published ahead of print 7 May 2014, doi: 10.1128/JVI.00894-14


ABSTRACT

More than 300 human infections with a novel avian H7N9 virus in China indicate that this emerging strain has pandemic potential. Furthermore, many of the H7N9 viruses circulating in animal reservoirs contain putative mammalian-signatures in the HA and PB2 genes that are believed to be important in the adaptation of other avian strains to humans. To date, the definitive role of these mammalian-signature substitutions in transmission and pathogenesis of H7N9 viruses remain unclear. To address this we analyzed biological characteristics, pathogenicity and transmissibility of A/Anhui/1/2013 (H7N9) virus and variants in vitro and in vivo: using a synthetically created wild type virus (rAnhui-WT) and two mutants (rAnhui-HA-226Q and rAnhui-PB2-627E). All three viruses replicated in lungs of intratracheally inoculated pigs, yet nasal shedding was limited. The rAnhui-WT and rAnhui-PB2-627E viruses transmitted to contact animals. In contrast, the rAnhui-HA-226Q virus did not transmit to sentinel pigs. Deep sequencing of viruses from the lungs of infected pigs identified substitutions arising in the viral population (e.g., PB2-T271A, PB2-D701N, HA-V195I, and PB2-E627K reversion) that may enhance viral replication in pigs. Collectively, the results demonstrate that critical mutations (i.e., HA-Q226L) are enabling the H7N9 viruses to transmit in a mammalian host, and suggest that the myriad of H7N9 genotypes circulating in avian species in China and closely related strains (e.g., H7N7) have the potential for further adaptation to human or other mammalian hosts (e.g., pigs) leading to strains capable of sustained human-to-human transmission.


Importance

The genomes of the zoonotic avian H7N9 viruses emerging in China have mutations in critical genes (PB2-E627K and HA-Q226L) that may be important in their pandemic potential. This study shows that: 1) the HA-226L of zoonotic H7N9 strains is critical for binding the α-2, 6 linked receptor and it enables transmission in pigs; 2) wild type A/Anhui/1/2013 (H7N9) shows modest replication, virulence and transmissibility in pigs, suggesting it is not well adapted to the mammalian host; and 3) both wild type and variant H7N9 viruses rapidly develop additional mammalian-signature mutations in pigs, indicating that they represent an important potential intermediate host. This is the first study analyzing the phenotypic effects of specific mutations within the HA and PB2 of the novel H7N9 viruses created by reverse genetics in an important mammalian host model. Finally, this study illustrates that loss-of-function mutations can be used to effectively identify residues critical to zoonosis/transmission.


FOOTNOTES

Correspondence to: Jürgen A. Richt, DVM, PhD, Kansas State University, College of Veterinary Medicine, Diagnostic Medicine/Pathobiology, K-224B Mosier Hall, 1800 Denison Ave., Manhattan, KS 66506-5601, USA, E-mail: jricht@ksu.edu; Phone: (001) 785-532-2793; Fax: (001) 785-532-3373

† David Wentworth, PhD, J. Craig Venter Institute, Virology, 9704 Medical Center Drive, Rockville, MD 20850 USA, E-mail:dwentworth@jcvi.org; Phone: (001) 301-795-7625

Copyright © 2014, American Society for Microbiology. All Rights Reserved.


-
------