Giuseppe
Emeritus
[Source: PLoS Pathogens, full text: (LINK). Abstract, edited.]
Acquisition of Human-Type Receptor Binding Specificity by New H5N1 Influenza Virus Sublineages during Their Emergence in Birds in Egypt
Yohei Watanabe<SUP>1</SUP><SUP>*</SUP>, Madiha S. Ibrahim<SUP>1</SUP><SUP>,</SUP><SUP>2</SUP><SUP>?</SUP>, Hany F. Ellakany<SUP>3</SUP>, Norihito Kawashita<SUP>4</SUP><SUP>,</SUP><SUP>5</SUP>, Rika Mizuike<SUP>1</SUP>, Hiroaki Hiramatsu<SUP>6</SUP>, Nogluk Sriwilaijaroen<SUP>6</SUP><SUP>,</SUP><SUP>7</SUP>, Tatsuya Takagi<SUP>4</SUP><SUP>,</SUP><SUP>5</SUP>, Yasuo Suzuki<SUP>6</SUP>, Kazuyoshi Ikuta<SUP>1</SUP><SUP>*</SUP>
1 Department of Virology, Research Institute for Microbial Diseases (BIKEN), Osaka University, Osaka, Japan, 2 Department of Microbiology, Faculty of Veterinary Medicine, Alexandria University, Damanhour Branch, Egypt, 3 Department of Poultry Diseases and Hygiene, Faculty of Veterinary Medicine, Alexandria University, Edfina Branch, Egypt, 4 Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan, 5 Genome Information Research Center, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan, 6 Health Scientific Hills, College of Life and Health Sciences, Chubu University, Aichi, Japan, 7 Faculty of Medicine, Thammasat University (Rangsit Campus), PathumThani, Thailand
Abstract
Highly pathogenic avian influenza A virus subtype H5N1 is currently widespread in Asia, Europe, and Africa, with 60% mortality in humans. In particular, since 2009 Egypt has unexpectedly had the highest number of human cases of H5N1 virus infection, with more than 50% of the cases worldwide, but the basis for this high incidence has not been elucidated. A change in receptor binding affinity of the viral hemagglutinin (HA) from α2,3- to α2,6-linked sialic acid (SA) is thought to be necessary for H5N1 virus to become pandemic. In this study, we conducted a phylogenetic analysis of H5N1 viruses isolated between 2006 and 2009 in Egypt. The phylogenetic results showed that recent human isolates clustered disproportionally into several new H5 sublineages suggesting that their HAs have changed their receptor specificity. Using reverse genetics, we found that these H5 sublineages have acquired an enhanced binding affinity for α2,6 SA in combination with residual affinity for α2,3 SA, and identified the amino acid mutations that produced this new receptor specificity. Recombinant H5N1 viruses with a single mutation at HA residue 192 or a double mutation at HA residues 129 and 151 had increased attachment to and infectivity in the human lower respiratory tract but not in the larynx. These findings correlated with enhanced virulence of the mutant viruses in mice. Interestingly, these H5 viruses, with increased affinity to α2,6 SA, emerged during viral diversification in bird populations and subsequently spread to humans. Our findings suggested that emergence of new H5 sublineages with α2,6 SA specificity caused a subsequent increase in human H5N1 influenza virus infections in Egypt, and provided data for understanding the virus's pandemic potential.
Author Summary
Even though highly pathogenic avian H5N1 influenza viruses lack an efficient mechanism for human-human transmission, these viruses are endemic in birds in China, Indonesia, Viet Nam and Egypt. Hotspots for bird-human transmission are indicated in areas where human cases are more than 80% of total H5N1 influenza cases. Circulation among hosts may allow H5N1 virus to acquire amino acid changes enabling efficient bird-human transmission and eventually human-human transmission. The receptor specificity of viral hemagglutinin (HA) is considered a main factor affecting efficient transmissibility. Several amino acid substitutions in H5 virus HAs that increase their human-type receptor specificity have been described in virus isolates from patients, but their prevalence has been limited. In contrast, we show here that new H5 sublineages in Egypt have acquired a change in receptor specificity during their diversification in birds. We found that viruses in those sublineages exhibited increased attachment and infectivity in the human lower respiratory tract, but not in the larynx. Our findings may not allow a conclusion on the high pandemic potential of H5N1 virus in Egypt, but helps explain why Egypt has recently had the highest number of human H5 cases worldwide.
Citation: Watanabe Y, Ibrahim MS, Ellakany HF, Kawashita N, Mizuike R, et al. (2011) Acquisition of Human-Type Receptor Binding Specificity by New H5N1 Influenza Virus Sublineages during Their Emergence in Birds in Egypt. PLoS Pathog 7(5): e1002068. doi:10.1371/journal.ppat.1002068
Editor: Ron A. M. Fouchier, Erasmus Medical Center, Netherlands
Received: December 22, 2010; Accepted: March 30, 2011; Published: May 26, 2011
Copyright: ? 2011 Watanabe et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was supported by a Grant-in Aid for Scientific Research (20406025) from the Ministry of Education, Culture, Sports, Science and Technology (http://www.mext.go.jp/english/), Japan (Scientific Research (B), Overseas Academic Research) and Global COE Program from the Japan Society for the Promotion of Science (http://www.jsps.go.jp/english/), Japan. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: nabe@biken.osaka-u.ac.jp (YW); Ikuta@biken.osaka-u.ac.jp (KI)
? Current address: Department of Microbiology, Faculty of Veterinary Medicine, Damanhour University, Damanhour, Egypt
- -------Yohei Watanabe<SUP>1</SUP><SUP>*</SUP>, Madiha S. Ibrahim<SUP>1</SUP><SUP>,</SUP><SUP>2</SUP><SUP>?</SUP>, Hany F. Ellakany<SUP>3</SUP>, Norihito Kawashita<SUP>4</SUP><SUP>,</SUP><SUP>5</SUP>, Rika Mizuike<SUP>1</SUP>, Hiroaki Hiramatsu<SUP>6</SUP>, Nogluk Sriwilaijaroen<SUP>6</SUP><SUP>,</SUP><SUP>7</SUP>, Tatsuya Takagi<SUP>4</SUP><SUP>,</SUP><SUP>5</SUP>, Yasuo Suzuki<SUP>6</SUP>, Kazuyoshi Ikuta<SUP>1</SUP><SUP>*</SUP>
1 Department of Virology, Research Institute for Microbial Diseases (BIKEN), Osaka University, Osaka, Japan, 2 Department of Microbiology, Faculty of Veterinary Medicine, Alexandria University, Damanhour Branch, Egypt, 3 Department of Poultry Diseases and Hygiene, Faculty of Veterinary Medicine, Alexandria University, Edfina Branch, Egypt, 4 Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan, 5 Genome Information Research Center, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan, 6 Health Scientific Hills, College of Life and Health Sciences, Chubu University, Aichi, Japan, 7 Faculty of Medicine, Thammasat University (Rangsit Campus), PathumThani, Thailand
Abstract
Highly pathogenic avian influenza A virus subtype H5N1 is currently widespread in Asia, Europe, and Africa, with 60% mortality in humans. In particular, since 2009 Egypt has unexpectedly had the highest number of human cases of H5N1 virus infection, with more than 50% of the cases worldwide, but the basis for this high incidence has not been elucidated. A change in receptor binding affinity of the viral hemagglutinin (HA) from α2,3- to α2,6-linked sialic acid (SA) is thought to be necessary for H5N1 virus to become pandemic. In this study, we conducted a phylogenetic analysis of H5N1 viruses isolated between 2006 and 2009 in Egypt. The phylogenetic results showed that recent human isolates clustered disproportionally into several new H5 sublineages suggesting that their HAs have changed their receptor specificity. Using reverse genetics, we found that these H5 sublineages have acquired an enhanced binding affinity for α2,6 SA in combination with residual affinity for α2,3 SA, and identified the amino acid mutations that produced this new receptor specificity. Recombinant H5N1 viruses with a single mutation at HA residue 192 or a double mutation at HA residues 129 and 151 had increased attachment to and infectivity in the human lower respiratory tract but not in the larynx. These findings correlated with enhanced virulence of the mutant viruses in mice. Interestingly, these H5 viruses, with increased affinity to α2,6 SA, emerged during viral diversification in bird populations and subsequently spread to humans. Our findings suggested that emergence of new H5 sublineages with α2,6 SA specificity caused a subsequent increase in human H5N1 influenza virus infections in Egypt, and provided data for understanding the virus's pandemic potential.
Author Summary
Even though highly pathogenic avian H5N1 influenza viruses lack an efficient mechanism for human-human transmission, these viruses are endemic in birds in China, Indonesia, Viet Nam and Egypt. Hotspots for bird-human transmission are indicated in areas where human cases are more than 80% of total H5N1 influenza cases. Circulation among hosts may allow H5N1 virus to acquire amino acid changes enabling efficient bird-human transmission and eventually human-human transmission. The receptor specificity of viral hemagglutinin (HA) is considered a main factor affecting efficient transmissibility. Several amino acid substitutions in H5 virus HAs that increase their human-type receptor specificity have been described in virus isolates from patients, but their prevalence has been limited. In contrast, we show here that new H5 sublineages in Egypt have acquired a change in receptor specificity during their diversification in birds. We found that viruses in those sublineages exhibited increased attachment and infectivity in the human lower respiratory tract, but not in the larynx. Our findings may not allow a conclusion on the high pandemic potential of H5N1 virus in Egypt, but helps explain why Egypt has recently had the highest number of human H5 cases worldwide.
Citation: Watanabe Y, Ibrahim MS, Ellakany HF, Kawashita N, Mizuike R, et al. (2011) Acquisition of Human-Type Receptor Binding Specificity by New H5N1 Influenza Virus Sublineages during Their Emergence in Birds in Egypt. PLoS Pathog 7(5): e1002068. doi:10.1371/journal.ppat.1002068
Editor: Ron A. M. Fouchier, Erasmus Medical Center, Netherlands
Received: December 22, 2010; Accepted: March 30, 2011; Published: May 26, 2011
Copyright: ? 2011 Watanabe et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was supported by a Grant-in Aid for Scientific Research (20406025) from the Ministry of Education, Culture, Sports, Science and Technology (http://www.mext.go.jp/english/), Japan (Scientific Research (B), Overseas Academic Research) and Global COE Program from the Japan Society for the Promotion of Science (http://www.jsps.go.jp/english/), Japan. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: nabe@biken.osaka-u.ac.jp (YW); Ikuta@biken.osaka-u.ac.jp (KI)
? Current address: Department of Microbiology, Faculty of Veterinary Medicine, Damanhour University, Damanhour, Egypt