title: Antigenic and genetic evolution of equine influenza A (H3N8) virus from 1968 to 2007.
abstract: Equine influenza virus is a major respiratory pathogen in horses, and outbreaks of disease often lead to substantial disruption to and economic losses for equestrian industries. The hemagglutinin (HA) protein is of key importance in the control of equine influenza because HA is the primary target of the protective immune response and the main component of currently licensed influenza vaccines. However, the influenza virus HA protein changes over time, a process called antigenic drift, and vaccine strains must be updated to remain effective. Antigenic drift is assessed primarily by the hemagglutination inhibition (HI) assay. We have generated HI assay data for equine influenza A (H3N8) viruses isolated between 1968 and 2007 and have used antigenic cartography to quantify antigenic differences among the isolates. The antigenic evolution of equine influenza viruses during this period was clustered: from 1968 to 1988, all isolates formed a single antigenic cluster, which then split into two cocirculating clusters in 1989, and then a third cocirculating cluster appeared in 2003. Viruses from all three clusters were isolated in 2007. In one of the three clusters, we show evidence of antigenic drift away from the vaccine strain over time. We determined that a single amino acid substitution was likely responsible for the antigenic differences among clusters.
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, United Kingdom. nsl25@cam.ac.uk
authors.forename: N S
authors.initials: NS
authors.lastname: Lewis
authors.forename: J M
authors.initials: JM
authors.lastname: Daly
authors.forename: C A
authors.initials: CA
authors.lastname: Russell
authors.forename: D L
authors.initials: DL
authors.lastname: Horton
authors.forename: E
authors.initials: E
authors.lastname: Skepner
authors.forename: N A
authors.initials: NA
authors.lastname: Bryant
authors.forename: D F
authors.initials: DF
authors.lastname: Burke
authors.forename: A S
authors.initials: AS
authors.lastname: Rash
authors.forename: J L N
authors.initials: JL
authors.lastname: Wood
authors.forename: T M
authors.initials: TM
authors.lastname: Chambers
authors.forename: R A M
authors.initials: RA
authors.lastname: Fouchier
authors.forename: J A
authors.initials: JA
authors.lastname: Mumford
authors.forename: D M
authors.initials: DM
authors.lastname: Elton
authors.forename: D J
authors.initials: DJ
authors.lastname: Smith
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000956:Antigens, Viral / Q000145:classification / Q000276:immunology; D015153:Blotting, Western; D002478:Cells, Cultured; D004285:Dogs; D019143:Evolution, Molecular; D006385:Hemagglutination Inhibition Tests; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics / Q000276:immunology*; D006388:Hemagglutinins / Q000276:immunology / Q000378:metabolism; D006736:Horses; D053123:Influenza A Virus, H3N8 Subtype / Q000235:genetics* / Q000276:immunology* / Q000302:isolation & purification; D007668:Kidney / Q000166:cytology / Q000378:metabolism / Q000821:virology; D009976:Orthomyxoviridae Infections / Q000235:genetics / Q000276:immunology / Q000821:virology*; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors
chemical_list: D000956:Antigens, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D006388:Hemagglutinins; D012333:RNA, Messenger; D012367:RNA, Viral