human infection caused by an avian influenza a h7n9 virus with a polybasic cleavage site in taiwan 2017

Human infection caused by an avian influenza A H7N9 virus with a polybasic cleavage site in Taiwan, 2017 Center for Diagnostics and Vaccine Development, Centers for Disease Control, Taip

Human infection caused by an avian

influenza A (H7N9) virus with a polybasic

cleavage site in Taiwan, 2017

Center for Diagnostics and Vaccine Development, Centers for Disease Control, Taipei, Taiwan

Received 20 February 2017; accepted 21 February 2017

On February 4, 2017, the Centers for Disease Control,

Taiwan reported the year’s first laboratory-confirmed

human infection with avian influenza A (H7N9) virus, by

three real-time reverse transcriptase polymerase chain

reactions targeting three different segments of the matrix

(M), hemagglutinin (HA), and neuraminidase (NA) genes

The patient is a 69-year old man who returned from the

Guangdong province of mainland China and is currently in

critical condition The avian influenza A virus was first

identified in March 2013 in China, and it was found to cause

a severe infection in humans.1In this report, the virus (A/

Taiwan/1/2017) was isolated from a sputum specimen of

the patient by inoculating into embryonated chicken eggs

The full-length genomic sequences were analyzed to

investigate the phylogenetic and genetic characteristics of

this virus (GISAID accession numbers EPI917062-EPI917069)

We constructed the phylogenetic trees for each genome

segment using the program MEGA6 (Tempe, Arizona, United

States) Based on the analyzed phylogenies, the A/Taiwan/

1/2017 virus is a novel reassortant belonging to a genotype

whose genetic constellation has not been reported

previously The HA and NA genes of this virus belong to the Yangtze River Delta lineage, along with the H7N9 viruses isolated from Jiangsu, Zhejiang, and Fujian provinces of China in 2016 and 2017 This lineage is distinguished from the Pearl River Delta lineage that mainly comprises the virus strains isolated from Hong Kong and Guangdong province since 2014 Phylogenies of the six internal genes of A/Taiwan/1/2017 revealed the viral PB1 and MP (matrix protein) genes located at clades together with those of the A/Anhui/1/2013 vaccine strain and recently isolated viruses from Jiangsu, Zhejiang, Fujian, and Guangdong provinces in

2016 and 2017 The PB2 (polymerase basic protein 2), PA (polymerase acidic protein), and NS (non-structural protein) genes clustered together with early H7N9 viruses and could be separated from those of the 2016 and 2017 viruses These results indicate that the H7N9 viruses are continuously evolving through reassortment

The molecular signatures of the A/Taiwan/1/2017 virus associated with host adaptation, receptor specificity, path-ogenesis, and antiviral resistance were also investigated (Table 1) The Q226L/I and G228S substitutions in the HA protein, which are the major two mutations contributing to the high-affinity binding of viruses to human receptors, were not identified in this virus However, several substitutions in

HA were detected, namely S138A, T160A, and G186V Of particular note, the A/Taiwan/1/2017 virus has an insertion

of three basic amino acid residues (RKR) at the cleavage site connecting the HA1 and HA2 peptide regions, carrying a signature (PKRKRTAR/GLF) of highly pathogenic avian influ-enza (HPAI) viruses This has been the first demonstration of

Conflicts of interest: The authors have no conflicts of interest

relevant to this article.

* Corresponding author Center for Diagnostics and Vaccine

Development, Centers for Disease Control, Number 161, Kun-Yang

Street, Taipei, 11561, Taiwan.

E-mail address: mtliu@cdc.gov.tw (M.-T Liu).

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http://dx.doi.org/10.1016/j.jfma.2017.02.011

0929-6646/Copyright ª 2017, Formosan Medical Association Published by Elsevier Taiwan LLC This is an open access article under the

CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

Available online atwww.sciencedirect.com

ScienceDirect

journal homepage: www jfma-online com Journal of the Formosan Medical Association (2017) xx, 1 e3

such a molecular characteristic in an H7N9 virus since their

emergence in 2013, according to the alignment of viral HA

sequences available from the GISAID database In the PB2

protein, the E627K substitution was present, as in previous

isolates.1,2 Virulence-related signatures, such as the 90

amino acid-PB1-F2 protein, as well as the P42S and D92E

substitutions in the NS1 protein, were also identified The

R292K substitution in the NA protein, which is a signature

related to antiviral drug susceptibility, was present in the A/

Taiwan/1/2017 virus, suggesting that this virus had

devel-oped resistance to oseltamivir The relationship of these

substitutions and the viral phenotype in avian and human

populations remains unknown

The polybasic HA cleavage site is considered the

pri-mary virulence marker of HPAI viruses.3 The low

patho-genic avian influenza subtypes H5 and H7 acquired

multiple basic amino acids at the HA cleavage site after

the viruses were introduced into domestic poultry.4 The

early H7N9 viruses lacked the polybasic HA cleavage site,

exhibiting low pathogenicity, and caused mild or no

dis-ease in poultry.1,5Based on our analysis, we found that

the H7N9 virus acquired an additional three basic amino

acids at the HA cleavage site for the first time, which

probably increased its virulence in poultry We proposed that the acquired polybasic insertion in this virus may be attributed to persistent circulation in poultry species, and the H7N9-infected poultry may be the primary source

of human infection Further investigation is needed to determine whether the polybasic HA cleavage site of the H7N9 virus is associated with more severe human disease Our results on the molecular characteristics of this novel H7N9 virus highlight challenges in risk assessment of the H7N9 virus at the human-animal interface

References

1 Gao R, Cao B, Hu Y, Feng Z, Wang D, Hu W, et al Human infection with a novel avian-origin influenza A (H7N9) virus N Engl J Med 2013;368:1888 e97

2 Yang JR, Kuo CY, Huang HY, Wu FT, Huang YL, Cheng CY, et al Characterization of influenza A (H7N9) viruses isolated from human cases imported into Taiwan PLoS One 2015;10:e0119792

3 Horimoto T, Kawaoka Y Reverse genetics provides direct ev-idence for a correlation of hemagglutinin cleavability and virulence of an avian influenza A virus J Virol 1994;68:

3120 e8

Table 1 Molecular analysis of the imported A/Taiwan/1/2017 H7N9 virus

Determination of viral characteristics

87e90 aa in length 90 aa Increased pathogenicity in mice

HA(H3 numbering) Cleavage site Basic aa insertion PEVP KRKR TARGL High pathogenesis in poultry

influenza receptor

binding to human-type influenza receptor

influenza receptor

influenza receptor

influenza receptor

aa Z amino acids; HA Z hemagglutinin; H3 Z hemagglutinin subtype 3; M2 Z matrix 2 protein; NA Z neuraminidase; N2 Z neuraminidase subtype 2; NS Z non-structural protein; PA Z polymerase acidic protein; PB Z polymerase basic protein; PB1-F2 Z polymerase basic protein 1 alternate reading frame 2.

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4 Horimoto T, Rivera E, Pearson J, Senne D, Krauss S, Kawaoka Y,

et al Origin and molecular changes associated with emergence

of a highly pathogenic H5N2 influenza virus in Mexico Virology

1995;213:223 e30

5 Chen Y, Liang W, Yang S, Wu N, Gao H, Sheng J, et al Human infections with the emerging avian influenza A H7N9 virus from wet market poultry: clinical analysis and characterisation of viral genome Lancet 2013;381:1916 e25

Human infection caused by an avian influenza A (H7N9) 3

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