title: Equine and Canine Influenza H3N8 Viruses Show Minimal Biological Differences Despite Phylogenetic Divergence.
abstract: The A/H3N8 canine influenza virus (CIV) emerged from A/H3N8 equine influenza virus (EIV) around the year 2000 through the transfer of a single virus from horses to dogs. We defined and compared the biological properties of EIV and CIV by examining their genetic variation, infection, and growth in different cell cultures, receptor specificity, hemagglutinin (HA) cleavage, and infection and growth in horse and dog tracheal explant cultures. Comparison of sequences of viruses from horses and dogs revealed mutations that may be linked to host adaptation and tropism. We prepared infectious clones of representative EIV and CIV strains that were similar to the consensus sequences of viruses from each host. The rescued viruses, including HA and neuraminidase (NA) double reassortants, exhibited similar degrees of long-term growth in MDCK cells. Different host cells showed various levels of susceptibility to infection, but no differences in infectivity were seen when comparing viruses. All viruses preferred α2-3- over α2-6-linked sialic acids for infections, and glycan microarray analysis showed that EIV and CIV HA-Fc fusion proteins bound only to α2-3-linked sialic acids. Cleavage assays showed that EIV and CIV HA proteins required trypsin for efficient cleavage, and no differences in cleavage efficiency were seen. Inoculation of the viruses into tracheal explants revealed similar levels of infection and replication by each virus in dog trachea, although EIV was more infectious in horse trachea than CIV.
  
  
  OBJECTIVE
  Influenza A viruses can cross species barriers and cause severe disease in their new hosts. Infections with highly pathogenic avian H5N1 virus and, more recently, avian H7N9 virus have resulted in high rates of lethality in humans. Unfortunately, our current understanding of how influenza viruses jump species barriers is limited. Our aim was to provide an overview and biological characterization of H3N8 equine and canine influenza viruses using various experimental approaches, since the canine virus emerged from horses approximately 15 years ago. We showed that although there were numerous genetic differences between the equine and canine viruses, this variation did not result in dramatic biological differences between the viruses from the two hosts, and the viruses appeared phenotypically equivalent in most assays we conducted. These findings suggest that the cross-species transmission and adaptation of influenza viruses may be mediated by subtle changes in virus biology.
authors.affiliation: Department of Microbiology and Immunology, Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
authors.forename: Kurtis H
authors.initials: KH
authors.lastname: Feng
authors.affiliation: Medical Research Council-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom.
authors.forename: Gaelle
authors.initials: G
authors.lastname: Gonzalez
authors.affiliation: Cellular and Molecular Medicine, Glycobiology Research and Training Center, University of California, San Diego, La Jolla, California, USA.
authors.forename: Lingquan
authors.initials: L
authors.lastname: Deng
authors.affiliation: Department of Chemistry, University of California, Davis, Davis, California, USA.
authors.forename: Hai
authors.initials: H
authors.lastname: Yu
authors.affiliation: Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
authors.forename: Victor L
authors.initials: VL
authors.lastname: Tse
authors.affiliation: Department of Microbiology and Immunology, Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
authors.forename: Lu
authors.initials: L
authors.lastname: Huang
authors.affiliation: Department of Microbiology and Immunology, Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
authors.forename: Kai
authors.initials: K
authors.lastname: Huang
authors.affiliation: Department of Microbiology and Immunology, Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
authors.forename: Brian R
authors.initials: BR
authors.lastname: Wasik
authors.affiliation: Infectious Disease Group, J. Craig Venter Institute, Rockville, Maryland, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhou
authors.affiliation: Infectious Disease Group, J. Craig Venter Institute, Rockville, Maryland, USA.
authors.forename: David E
authors.initials: DE
authors.lastname: Wentworth
authors.affiliation: Marie Bashir Institute for Infectious Diseases and Biosecurity, Charles Perkins Centre, School of Biological Sciences and Sydney Medical School, The University of Sydney, Sydney, New South Wales, Australia.
authors.forename: Edward C
authors.initials: EC
authors.lastname: Holmes
authors.affiliation: Department of Chemistry, University of California, Davis, Davis, California, USA.
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.affiliation: Cellular and Molecular Medicine, Glycobiology Research and Training Center, University of California, San Diego, La Jolla, California, USA.
authors.forename: Ajit
authors.initials: A
authors.lastname: Varki
authors.affiliation: Medical Research Council-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom.
authors.forename: Pablo R
authors.initials: PR
authors.lastname: Murcia
authors.affiliation: Department of Microbiology and Immunology, Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA crp3@cornell.edu.
authors.forename: Colin R
authors.initials: CR
authors.lastname: Parrish
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D002460:Cell Line; D004285:Dogs; D014644:Genetic Variation; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000378:metabolism; D006736:Horses; D053123:Influenza A Virus, H3N8 Subtype / Q000235:genetics* / Q000254:growth & development / Q000302:isolation & purification / Q000502:physiology*; D009154:Mutation; D010802:Phylogeny; D011485:Protein Binding; D011991:Receptors, Virus / Q000378:metabolism; D012794:Sialic Acids / Q000378:metabolism; D014132:Trachea / Q000821:virology*; D056189:Viral Tropism; D053585:Virus Attachment
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; D011991:Receptors, Virus; D012794:Sialic Acids