Recent evolution of equine influenza and the origin of canine influenza

In late 2011, an A(H3N8) influenza virus infection resulted in the deaths IMPORTANCECross-species transmission of zoonotic influenza viruses increases public health concerns. Here, we report a molecular and structural study of the major surface proteins from an A(H3N8) influenza virus isolated from New England harbor seals. The results improve our understanding of these viruses as they evolve and provide important information to aid ongoing risk assessment analyses as these zoonotic influenza viruses continue to circulate and adapt to new hosts. Influenza A viruses (IAVs) are classified into subtypes according to the serological reactivity of their surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA) (1, 2). While 16 HA (H1 to H16) and 9 NA (N1 to N9) subtypes have been identified in wild aquatic birds in the last 100 years, only 3 have adapted to the human population, resulting in four pandemics: H1N1 in 1918 and 2009, H2N2 in 1957, and H3N2 in 1968 (3-6). Although aquatic birds are believed to be the natural reservoir for influenza viruses (7), two novel subtypes of influenza A viruses, H17N10 and H18N11, were recently described in New World bats, which thus may be an alternate reservoir of influenza viruses in nature (8,9).Since the first isolation of H1N1 IAV in swine (10) and the subsequent observation that ferrets were susceptible to IAV (11), it became evident that multiple IAV subtypes of either avian or human descent can infect a number of mammalian species (1). Indeed, over the last decade, the perception and impact of influenza virus infections in animals have changed dramatically as a result of a number of recent outbreaks in poultry involving viruses from the H5, H7, and H9 subtypes that resulted in Ͼ1,000 human infections, as well as the swine origin of the recent A(H1N1)pdm09 pandemic virus (4,(12)(13)(14). This has prompted some governments to invest heavily in global surveillance, research, and capacity building. Public health officials now have a keen interest in all IAVs, but particularly in whether animals, such as pigs, that are closely associated with humans can represent a possible pathway for increased interspecies virus adaptation and transmission.Similar to the infection of pigs, IAV (i.e., H7N7, H4N5, H3N3, H13N2, H13N9, and H4N6 subtypes) and influenza B virus infections have been detected in marine mammals, including seals, whales, and sea otters (15)(16)(17)(18)(19)(20)(21)(22). In November 2011, a marine mammal "unusual mortality event" was declared for Maine, New Hampshire, and northern Massachusetts in response to a large number of deaths in the New England harbor seal population. Sequence analysis revealed that an avian-like H3N8 influenza A virus, A/harbor seal/Massachusetts/1/2011 (seal11), was the cause of the outbreak (23). Although A(H3N8), usually found in avian, canine, equine, and swine hosts (24-27), had been isolated from a seal prior to this event (28), the high mortality observed increased interest from public health officials.Here, we focus our...

Section: Resultsmentioning

confidence: 99%

Structural and Functional Analysis of Surface Proteins from an A(H3N8) Influenza Virus Isolated from New England Harbor Seals

Yang

Nguyen

Carney

et al. 2015

“…More importantly, however, they are useful in highlighting prospective targets for broad-spectrum anti-influenza therapies and vaccines. In addition to seasonal influenza virus epidemics, it is evident from recent reports that outbreaks of variant H3N2 viruses and sporadic zoonotic transmissions of other group 2 viruses (e.g., H3N8, H10N8, and H7N9) are always a cause for concern (48)(49)(50)(51). With these ever-present threats to public health, the discovery and characterization of conserved epitopes in influenza virus would allow for better design of therapeutics and vaccines that would afford broad coverage.…”

Section: Discussionmentioning

confidence: 99%

Characterization of a Broadly Neutralizing Monoclonal Antibody That Targets the Fusion Domain of Group 2 Influenza A Virus Hemagglutinin

Tan

Lee

Hoffman

et al. 2014

114

113

Due to continuous changes to its antigenic regions, influenza viruses can evade immune detection and cause a significant amount of morbidity and mortality around the world. Influenza vaccinations can protect against disease but must be annually reformulated to match the current circulating strains. In the development of a broad-spectrum influenza vaccine, the elucidation of conserved epitopes is paramount. To this end, we designed an immunization strategy in mice to boost the humoral response against conserved regions of the hemagglutinin (HA) glycoprotein. Of note, generation and identification of broadly neutralizing antibodies that target group 2 HAs are rare and thus far have yielded only a few monoclonal antibodies (MAbs). Here, we demonstrate that mouse MAb 9H10 has broad and potent in vitro neutralizing activity against H3 and H10 group 2 influenza A subtypes. In the mouse model, MAb 9H10 protects mice against two divergent mouse-adapted H3N2 strains, in both pre-and postexposure administration regimens. In vitro and cell-free assays suggest that MAb 9H10 inhibits viral replication by blocking HA-dependent fusion of the viral and endosomal membranes early in the replication cycle and by disrupting viral particle egress in the late stage of infection. Interestingly, electron microscopy reconstructions of MAb 9H10 bound to the HA reveal that it binds a similar binding footprint to MAbs CR8020 and CR8043. IMPORTANCEThe influenza hemagglutinin is the major antigenic target of the humoral immune response. However, due to continuous antigenic changes that occur on the surface of this glycoprotein, influenza viruses can escape the immune system and cause significant disease to the host. Toward the development of broad-spectrum therapeutics and vaccines against influenza virus, elucidation of conserved regions of influenza viruses is crucial. Thus, defining these types of epitopes through the generation and characterization of broadly neutralizing monoclonal antibodies (MAbs) can greatly assist others in highlighting conserved regions of hemagglutinin. Here, we demonstrate that MAb 9H10 that targets the hemagglutinin stalk has broadly neutralizing activity against group 2 influenza A viruses in vitro and in vivo.

“…These multifactorial traits have been genetically linked to a number of the eight gene segments depending on the viral strain, host system, or phenotypic readout utilized in any particular study; however, properties of the HA often play a particularly significant role (2,(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). The receptor binding characteristics of HA have long been associated with host specificity (21-26), but more recently, a greater appreciation has developed for the role of HA stability in transmission, adaptation, and pathogenicity phenotypes (27)(28)(29)(30)(31)(32)(33)(34)(35)(36).HA stability phenotypes are intricately related to the pH at which the HA mediates endosomal membrane fusion during the virus entry process and, from a structural perspective, stability relates primarily to the postcleavage neutral pH conformation of …”

mentioning

confidence: 99%

Influenza Hemagglutinin (HA) Stem Region Mutations That Stabilize or Destabilize the Structure of Multiple HA Subtypes

Byrd-Leotis

Galloway

Agbogu

et al. 2015

Influenza A viruses enter host cells through endosomes, where acidification induces irreversible conformational changes of the viral hemagglutinin (HA) that drive the membrane fusion process. The prefusion conformation of the HA is metastable, and the pH of fusion can vary significantly among HA strains and subtypes. Furthermore, an accumulating body of evidence implicates HA stability properties as partial determinants of influenza host range, transmission phenotype, and pathogenic potential. Although previous studies have identified HA mutations that can affect HA stability, these have been limited to a small selection of HA strains and subtypes. Here we report a mutational analysis of HA stability utilizing a panel of expressed HAs representing a broad range of HA subtypes and strains, including avian representatives across the phylogenetic spectrum and several human strains. We focused on two highly conserved residues in the HA stem region: HA2 position 58, located at the membrane distal tip of the short helix of the hairpin loop structure, and HA2 position 112, located in the long helix in proximity to the fusion peptide. We demonstrate that a K58I mutation confers an acid-stable phenotype for nearly all HAs examined, whereas a D112G mutation consistently leads to elevated fusion pH. The results enhance our understanding of HA stability across multiple subtypes and provide an additional tool for risk assessment for circulating strains that may have other hallmarks of human adaptation. Furthermore, the K58I mutants, in particular, may be of interest for potential use in the development of vaccines with improved stability profiles. IMPORTANCEThe influenza A hemagglutinin glycoprotein (HA) mediates the receptor binding and membrane fusion functions that are essential for virus entry into host cells. While receptor binding has long been recognized for its role in host species specificity and transmission, membrane fusion and associated properties of HA stability have only recently been appreciated as potential determinants. We show here that mutations can be introduced at highly conserved positions to stabilize or destabilize the HA structure of multiple HA subtypes, expanding our knowledge base for this important phenotype. The practical implications of these findings extend to the field of vaccine design, since the HA mutations characterized here could potentially be utilized across a broad spectrum of influenza virus subtypes to improve the stability of vaccine strains or components. N early every year seasonal influenza A viruses contribute to hundreds of thousands of human deaths worldwide and place an extraordinary burden on health care systems and the global economy. Of even greater concern is the unpredictable appearance of antigenically novel influenza A strains in humans, with the potential for causing devastating pandemics. A major obstacle for controlling influenza is the diversity of influenza virus A strains that circulate in the avian species, since this provides a vast genetic pool of vi...