Robert G Webster

King Abdulaziz University, Djidda, Makkah, Saudi Arabia

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Publications (478)2593.75 Total impact

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    ABSTRACT: Influenza pandemics require that a virus containing a hemagglutinin (HA) surface antigen previously unseen by a majority of the population becomes airborne-transmissible between humans. Although the HA protein is central to the emergence of a pandemic influenza virus, its required molecular properties for sustained transmission between humans are poorly defined. During virus entry, the HA protein binds receptors and is triggered by low pH in the endosome to cause membrane fusion; during egress, HA contributes to virus assembly and morphology. In 2009, a swine influenza virus (pH1N1) jumped to humans and spread globally. Here we link the pandemic potential of pH1N1 to its HA acid stability, or the pH at which this one-time-use nanomachine is either triggered to cause fusion or becomes inactivated in the absence of a target membrane. In surveillance isolates, our data show HA activation pH values decreased during the evolution of H1N1 from precursors in swine (pH 5.5-6.0), to early 2009 human cases (pH 5.5), and then to later human isolates (pH 5.2-5.4). A loss-of-function pH1N1 virus with a destabilizing HA1-Y17H mutation (pH 6.0) was less pathogenic in mice and ferrets, less transmissible by contact, and no longer airborne-transmissible. A ferret-adapted revertant (HA1-H17Y/HA2-R106K) regained airborne transmissibility by stabilizing HA to an activation pH of 5.3, similar to that of human-adapted isolates from late 2009-2014. Overall, these studies reveal that a stable HA (activation pH ≤ 5.5) is necessary for pH1N1 influenza virus pathogenicity and airborne transmissibility in ferrets and is associated with pandemic potential in humans.
    No preview · Article · Jan 2016 · Proceedings of the National Academy of Sciences
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    ABSTRACT: Migratory aquatic birds play an important role in the maintenance and spread of avian influenza viruses (AIV). Many species of aquatic migratory birds tend to use similar migration routes, also known as flyways, which serve as important circuits for the dissemination of AIV. In recent years there has been extensive surveillance of the virus in aquatic birds in the Northern Hemisphere; however in contrast only a few studies have been attempted to detect AIV in wild birds in South America. There are major flyways connecting South America to Central and North America, whereas avian migration routes between South America and the remaining continents are uncommon. As a result, it has been hypothesized that South American AIV strains would be most closely related to the strains from North America than to those from other regions in the world. We characterized the full genome of three AIV subtype H11N9 isolates obtained from ruddy turnstones (Arenaria interpres) on the Amazon coast of Brazil. For all gene segments, all three strains consistently clustered together within evolutionary lineages of AIV that had been previously described from aquatic birds in North America. In particular, the H11N9 isolates were remarkably closely related to AIV strains from shorebirds sampled at the Delaware Bay region, on the Northeastern coast of the USA, more than 5000 km away from where the isolates were retrieved. Additionally, there was also evidence of genetic similarity to AIV strains from ducks and teals from interior USA and Canada. These findings corroborate that migratory flyways of aquatic birds play an important role in determining the genetic structure of AIV in the Western hemisphere, with a strong epidemiological connectivity between North and South America.
    Full-text · Article · Dec 2015 · PLoS ONE
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    ABSTRACT: Avian influenza A(H9N2) is an agricultural and public health threat. We characterized an H9N2 virus from a pet market in Bangladesh and demonstrated replication in samples from pet birds, swine tissues, human airway and ocular cells, and ferrets. Results implicated pet birds in the potential dissemination and zoonotic transmission of this virus.
    Preview · Article · Dec 2015 · Emerging infectious diseases
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    ABSTRACT: Objectives: Ducks can shed and spread influenza A viruses (IAVs) while showing no disease signs. Our objective was to clarify the role of 'foie gras' ducks in the circulation of IAVs in Bulgaria. Methods: Monthly avian influenza surveillance was conducted on 63 'foie gras' duck farms, 52 of which were surveyed throughout the study between November 2008 and April 2012. Virologic and serologic samples were collected and tested. During this time, wild bird samples were collected at major wild-bird resting areas near the Black Sea coast and Danube River. Results: The study showed high isolation frequency of low-pathogenicity avian influenza viruses. In the raising population (<75-days-old), subtypes H3, H4, and H6 were detected monthly and H5 LPAIV, sporadically. Different subtypes (H1, H10, H11) were isolated from the fattening premises (75- to 100-day-old ducks), suggesting different routes of introduction. Only 6 of the 52 farms that were surveyed both, virologically and serologically were influenza-free throughout the study, possibly due to higher biosecurity measures implemented. No evidence of direct transmission of IAV from wild birds was found. Wild-bird surveillance showed low isolation frequency of IAV. IAV prevalence of 0.55% for migratory ducks and 0.53% for migratory geese was estimated in Nov-Dec'2011 and Jan-Feb'2012, respectively, at two ornithologically important locations near the Black Sea coast. Conclusions: The 'foie gras' duck farms in Bulgaria are an optimal niche where Eurasian-like IAVs are maintained and reassorted unapparent to farmers and veterinarians. This article is protected by copyright. All rights reserved.
    Preview · Article · Dec 2015 · Influenza and Other Respiratory Viruses
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    ABSTRACT: We previously demonstrated that H9N2 subtype avian influenza viruses (AIVs) isolated from 1994 to 2008 evolved into distinct antigenic groups (C, D, and E) and then underwent antigenic drift from commercial vaccines, causing a country-wide outbreak during 2010–2013. In this study, H9N2 AIVs isolated from chickens during 2009–2013 were antigenically analyzed by performing hemagglutination inhibition and neutralization assays using a panel of polyclonal antibodies. Our findings confirmed the antigenic drift of recent H9N2 viruses from the commercial vaccine and showed that most of these antigenic variants form a novel HI antigenic group, F, with a few belonging to groups D and E. Slight antigenic variation was observed in group F viruses. Genetic analysis of amino acid sequences deduced from hemagglutinin (HA) gene sequences indicated that 9 of 15 mutations predominant in the 2009-2013 viruses can be mapped to known antigenic sites, which might be responsible for the novel antigenicity of group F. These antigenic changes make it necessary to modify the influenza vaccine to ensure efficient protection. A vaccine candidate, Ck/HeB/YT/10, was selected and provided significant protection against viruses from different antigenic groups in terms of reduction in virus shedding, suggesting broad cross-reactivity. Taken together, our results indicate that the H9N2 chicken influenza viruses in China have evolved from distinct antigenic groups into a novel group F that became dominant during the country-wide outbreak and now seems to be undergoing new antigenic divergence. Systematic surveillance and timely updating of vaccine strains are important for viral prevention and control in the future.
    No preview · Article · Nov 2015
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    ABSTRACT: Importance: Immune IFITM genes are poorly conserved across species suggesting that selective pressure from host-specific viruses has driven this divergence. We wondered whether co-evolution between viruses and their natural host would result in evasion of IFITM restriction. Ducks are the natural host of avian influenza A viruses (IAV) and display little to no disease symptoms upon infection with most strains, including highly pathogenic avian influenza. We have characterized the duck IFITM locus, and identified IFITM3 as an important restrictor of several influenza A viruses, including avian strains. With only 38% amino acid identity to human IFITM3, duck IFITM3 possesses antiviral function against influenza. Thus, despite long co-evolution of virus and host effectors in the natural host, influenza evasion of IFITM3 restriction in ducks is not apparent.
    No preview · Article · Oct 2015 · Journal of Virology
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    ABSTRACT: Importance: The number of humans infected with avian influenza viruses is increasing, raising concerns of the emergence of avian influenza viruses resistant to neuraminidase (NA) inhibitors (NAIs). As most studies have focused on NAI-resistance in human influenza viruses, here we investigated the molecular changes in NA that could confer NAI-resistance in avian viruses grown in immortalized monolayer cells, especially those of the N3, N7 and N9 subtypes, which have caused human infections. We identified not only numerous NAI-resistant substitutions previously reported in other NA subtypes but also several novel changes conferring reduced susceptibility to NAIs, which are subtype-specific. The findings indicate that some resistance markers are common across NA subtypes but other markers needs to be determined empirically for each subtype. The study also implies that antiviral surveillance monitoring could play a critical role in the clinical management of influenza infection and an essential component of pandemic preparedness.
    Full-text · Article · Aug 2015 · Journal of Virology
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    ABSTRACT: The virologic factors that limit the transmission of swine influenza viruses between humans are unresolved. While it has been shown that acquisition of the neuraminidase (NA) and matrix (M) gene segments from a Eurasian-lineage swine virus was required for airborne transmission of the 2009 pandemic H1N1 virus (H1N1pdm09), we show here that an arginine to lysine change in the hemagglutinin (HA) was also necessary. This change at position 149 was distal to the receptor binding site but affected virus-receptor affinity and HA dynamics, allowing the virus to replicate more efficiently in nasal turbinate epithelium and subsequently transmit between ferrets. Receptor affinity should be considered as a factor limiting swine virus spread in humans.
    Full-text · Article · Aug 2015 · Scientific Reports
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    Dataset: FigS1

    Full-text · Dataset · Aug 2015
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    Dataset: FigS2

    Full-text · Dataset · Aug 2015
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    Dataset: DataSet1

    Full-text · Dataset · Aug 2015
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    Full-text · Dataset · Aug 2015
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    Dataset: DataSet2

    Full-text · Dataset · Aug 2015
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    Dataset: FigS3

    Full-text · Dataset · Aug 2015
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    ABSTRACT: Wild waterfowl, including mallard ducks, are the natural reservoir of avian influenza A virus and they are resistant to strains that would cause fatal infection in chickens. Here we investigate potential involvement of TRIM proteins in the differential response of ducks and chickens to influenza. We examine a cluster of TRIM genes located on a single scaffold in the duck genome, which is a conserved synteny group with a TRIM cluster located in the extended MHC region in chickens and turkeys. We note a TRIM27-like gene is present in ducks, and absent in chickens and turkeys. Orthologous genes are predicted in many birds and reptiles, suggesting the gene has been lost in chickens and turkeys. Using quantitative real-time PCR (qPCR) we show that TRIM27-L, and the related TRIM27.1, are upregulated 5- and 9-fold at 1 day post-infection with highly pathogenic A/Vietnam/1203/2004. To assess whether TRIM27.1 or TRIM27-L are involved in modulation of antiviral gene expression, we overexpressed them in DF1 chicken cells, and neither show any direct effect on innate immune gene expression. However, when co-transfected with duck RIG-I-N (d2CARD) to constitutively activate the MAVS pathway, TRIM27.1 weakly decreases, while TRIM27-L strongly activates innate immune signaling leading to increased transcription of antiviral genes MX1 and IFN-β. Furthermore, when both are co-expressed, the activation of the MAVS signaling pathway by TRIM27-L over-rides the inhibition by TRIM27.1. Thus, ducks have an activating TRIM27-L to augment MAVS signaling following RIG-I detection, while chickens lack both TRIM27-L and RIG-I itself. Copyright © 2015 Elsevier Ltd. All rights reserved.
    No preview · Article · Aug 2015 · Molecular Immunology
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    ABSTRACT: Chickens are susceptible to infection with a limited number of Influenza A viruses and are a potential source of a human influenza pandemic. In particular, H5 and H7 haemagglutinin subtypes can evolve from low to highly pathogenic strains in gallinaceous poultry. Ducks on the other hand are a natural reservoir for these viruses and are able to withstand most avian influenza strains. Transcriptomic sequencing of lung and ileum tissue samples from birds infected with high (H5N1) and low (H5N2) pathogenic influenza viruses has allowed us to compare the early host response to these infections in both these species. Chickens (but not ducks) lack the intracellular receptor for viral ssRNA, RIG-I and the gene for an important RIG-I binding protein, RNF135. These differences in gene content partly explain the differences in host responses to low pathogenic and highly pathogenic avian influenza virus in chicken and ducks. We reveal very different patterns of expression of members of the interferon-induced transmembrane protein (IFITM) gene family in ducks and chickens. In ducks, IFITM1, 2 and 3 are strongly up regulated in response to highly pathogenic avian influenza, where little response is seen in chickens. Clustering of gene expression profiles suggests IFITM1 and 2 have an anti-viral response and IFITM3 may restrict avian influenza virus through cell membrane fusion. We also show, through molecular phylogenetic analyses, that avian IFITM1 and IFITM3 genes have been subject to both episodic and pervasive positive selection at specific codons. In particular, avian IFITM1 showed evidence of positive selection in the duck lineage at sites known to restrict influenza virus infection. Taken together these results support a model where the IFITM123 protein family and RIG-I all play a crucial role in the tolerance of ducks to highly pathogenic and low pathogenic strains of avian influenza viruses when compared to the chicken.
    Full-text · Article · Aug 2015 · BMC Genomics
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    ABSTRACT: Among the influenza A viruses (IAVs) in wild aquatic birds, only H1, H2, and H3 subtypes have caused epidemics in humans. H1N1 viruses of avian origin have also caused 3 of 5 pandemics. To understand the reappearance of H1N1 in the context of pandemic emergence , we investigated whether avian H1N1 IAVs have contributed to the evolution of human, swine, and 2009 pandemic H1N1 IAVs. On the basis of phylogenetic analysis, we concluded that the polymerase gene segments (especially PB2 and PA) circulating in North American avian H1N1 IAVs have been reintroduced to swine multiple times, resulting in different lineages that led to the emergence of the 2009 pandemic H1N1 IAVs. Moreover, the similar topologies of hemagglutinin and nucleoprotein and neuraminidase and matrix gene segments suggest that each surface glycoprotein coevolved with an internal gene segment within the H1N1 subtype. The genotype of avian H1N1 IAVs of Charadriiformes origin isolated in 2009 differs from that of avian H1N1 IAVs of Anseriformes origin. When the anti-genic sites in the hemagglutinin of all 31 North American avian H1N1 IAVs were considered, 60%-80% of the amino acids at the antigenic sites were identical to those in 1918 and/or 2009 pandemic H1N1 viruses. Thus, although the pathogenicity of avian H1N1 IAVs could not be inferred from the phylogeny due to the small dataset, the evolutionary process within the H1N1 IAV subtype suggests that the circulation of H1N1 IAVs in wild birds poses a continuous threat for future influenza pandemics in humans.
    Full-text · Article · Jul 2015 · PLoS ONE
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    ABSTRACT: Influenza A viruses of the H1N1 subtype have emerged from the avian influenza gene pool in aquatic birds and caused human pandemics at least twice during the past century. Despite this fact, surprisingly little is known about the H1N1 gene pool in the aquatic bird reservoir. A preliminary study showed that an H1N1 virus from a shorebird of the Charadriiformes order was transmitted between animals through the airborne route of infection, whereas an H1N1 virus from a bird of the Anseriformes order was not. Here we show that two of the three H1N1 viruses isolated from Charadriiformes species in 2009 were transmitted between animals through the airborne route of infection, and five H1N1 isolates from Anseriformes species were not. The one H1N1 virus from a Charadriiformes species that failed to transmit through the airborne route was a reassortant possessing multiple internal gene segments from Anseriformes species. The molecular differences between the airborne-transmissible and non-airborne-transmissible H1N1 viruses were multigenic, involving the selection of virus with human-like receptor-binding specificity (a2-6 sialic acid) and multiple differences in the polymerase complex, mainly in the PB2, PB1-F2, and nonstructural genes.
    Full-text · Article · Jul 2015 · Emerging Microbes and Infections
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    ABSTRACT: The emergence of influenza A virus (IAV) in domestic avian species and associated transmissions to mammals is unpredictable. In the Americas, the H7 IAVs are of particular concern, and there have been four separate outbreaks of highly pathogenic (HP) H7N3 in domestic poultry in North and South America between 2002 and 2012, with occasional spillover into humans. Here, we use long-term IAV surveillance in North American shorebirds at Delaware Bay, USA, from 1985 to 2012 and in ducks in Alberta, Canada, from 1976 to 2012 to determine which hemagglutinin (HA)–neuraminidase (NA) combinations predominated in Anseriformes (ducks) and Charadriiformes (shorebirds) and whether there is concordance between peaks of H7 prevalence and transmission in wild aquatic birds and the emergence of H7 IAVs in poultry and humans. Whole-genome sequencing supported phylogenetic and genomic constellation analyses to determine whether HP IAVs emerge in the context of specific internal gene segment sequences. Phylogenetic analysis of whole-genome sequences of the H7N3 influenza viruses from wild birds and HP H7N3 outbreaks in the Americas indicate that each HP outbreak was an independent emergence event and that the low pathogenic (LP) avian influenza precursors were most likely from dabbling ducks. The different polybasic cleavage sites in the four HP outbreaks support independent origins. At the 95% nucleotide percent identity-level phylogenetic analysis showed that the wild duck HA, PB1, and M sequences clustered with the poultry and human outbreak sequences. The genomic constellation analysis strongly suggests that gene segments/virus flow from wild birds to domestic poultry.
    Preview · Article · Jun 2015 · Emerging Microbes and Infections
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    ABSTRACT: The recently detected zoonotic H3N2 variant influenza A (H3N2v) viruses have caused 343 documented cases of human infection linked to contact with swine. An effective vaccine is needed for these viruses, which may acquire easy transmissibility among humans. However, viruses isolated from human cases do not replicate well in embryonated chicken eggs, posing an obstacle to egg-based vaccine production. To address this issue, we sought to identify egg-adaptive mutations in surface proteins that increase the yield of candidate vaccine viruses (CVVs) in eggs while preserving their immunizing effectiveness. After serial passage of a representative H3N2v isolate (A/Indiana/08/2011), we identified several egg-adaptive combinations of HA mutations and assessed the egg-based replication, antigenicity, and immunogenicity of A/Puerto Rico/8/34 (H1N1, PR8)-based 6+2 reverse genetics CVVs carrying these mutations. Here we demonstrate that the respective combined HA substitutions G1861V+N2461K, N1651K+G1861V, T1281N+N1651K+R762G, and T1281N+N1651K+I102M, all identified after egg passage, enhanced the replication of the CVVs in eggs without substantially affecting their antigenicity or immunogenicity. The mutations were stable, and the mutant viruses acquired no additional substitutions during six subsequent egg passages. We found two crucial mutations, G186V, which was previously defined, and N246K, which in combination improved virus yield in eggs without significantly impacting antigenicity or immunogenicity. This combination of egg-adaptive mutations appears to most effectively generate high egg-based yields of influenza A/Indiana/08/2011-like CVVs. Copyright © 2015. Published by Elsevier Ltd.
    No preview · Article · May 2015 · Vaccine

Publication Stats

31k Citations
2,593.75 Total Impact Points


  • 2015
    • King Abdulaziz University
      • Faculty of Sciences
      Djidda, Makkah, Saudi Arabia
  • 1975-2015
    • St. Jude Children's Research Hospital
      • Department of Infectious Diseases
      Memphis, Tennessee, United States
  • 2012
    • The Scripps Research Institute
      La Jolla, California, United States
  • 2003-2011
    • The University of Hong Kong
      • Department of Microbiology
      Hong Kong, Hong Kong
  • 2010
    • Korea Research Institute of Bioscience and Biotechnology KRIBB
      • Viral Infectious Disease Research Center
      Anzan, Gyeonggi Province, South Korea
    • University of Alberta
      • Department of Biological Sciences
      Edmonton, Alberta, Canada
  • 2002-2010
    • University of Tennessee
      • Department of Pathology
      Knoxville, Tennessee, United States
    • University of Naples Federico II
      Napoli, Campania, Italy
    • University of Virginia
      • Division of Maternal Fetal Medicine
      Charlottesville, Virginia, United States
  • 2005-2007
    • Ivanovsky Institute of Virology
      Moskva, Moscow, Russia
    • Centers for Disease Control and Prevention
      Atlanta, Michigan, United States
    • Shantou University
      • International Institute of Infection and Immunity
      Swatow, Guangdong, China
    • National Institute of Veterinary Research, Vietnam
      Hà Nội, Ha Nội, Vietnam
  • 2006
    • University of Michigan
      • School of Public Health
      Ann Arbor, Michigan, United States
  • 2002-2005
    • Philipps University of Marburg
      • Institut für Virologie
      Marburg, Hesse, Germany
  • 2004
    • University of Maryland, College Park
      • Virginia-Maryland Regional College of Veterinary Medicine
      CGS, Maryland, United States
    • University of California, Davis
      Davis, California, United States
  • 2001
    • The University of Memphis
      Memphis, Tennessee, United States
  • 1992-1997
    • University of Massachusetts Medical School
      • Department of Pathology
      Worcester, MA, United States
  • 1994
    • Erasmus Universiteit Rotterdam
      • Department of Virology
      Rotterdam, South Holland, Netherlands
  • 1987-1990
    • University of Alabama at Birmingham
      • Department of Microbiology
      Birmingham, AL, United States
  • 1986
    • Hokkaido University
      • Laboratory of Radiation Biology
      Sapporo, Hokkaidō, Japan
  • 1985
    • National Institute for Biological Standards and Control
      • Division of Virology
      Potters Bar, England, United Kingdom
    • The University of Tennessee Health Science Center
      • Department of Microbiology, Immunology and Biochemistry
      Memphis, Tennessee, United States