title: Phylogenetic and molecular characterization of equine H3N8 influenza viruses from Greece (2003 and 2007): evidence for reassortment between evolutionary lineages.
abstract: BACKGROUND
  For first time in Greece equine influenza virus infection was confirmed, by isolation and molecular analysis, as the cause of clinical respiratory disease among unvaccinated horses during 2003 and 2007 outbreaks.
  
  
  METHODS
  Equine influenza virus (EIV) H3N8 was isolated in MDCK cells from 30 nasal swabs from horses with acute respiratory disease, which were tested positive by Directigen Flu A. Isolation was confirmed by haemagglutination assay and RT-PCR assay of the M, HA and NA gene.
  
  
  RESULTS
  HA sequences of the Greek isolates appeared to be more closely related to viruses isolated in early 1990s in Europe. These results suggested that viruses with fewer changes than those on the main evolutionary lineage may continue to circulate. On the other hand, analysis of deduced NA amino acid sequences were more closely related to viruses isolated in outbreaks in Europe and Asia during 2003-2007. Phylogenetic analysis characterized the Greek isolates as a member of the Eurasian lineage by the haemagglutinin (HA) protein alignment, but appeared to be a member of the Florida sublineage clade 2 by the neuraminidase (NA) protein sequence suggesting that reassortment might be a possible explanation.
  
  
  CONCLUSIONS
  Our findings suggest that the Greek strains represent an example of "frozen evolution" and probably reassortment between genetically distinct co-circulated strains. Therefore expanding current equine influenza surveillance efforts is a necessity.
authors.affiliation: Department of Anatomy and Physiology of Farm Animals, Faculty of Animal Science and Aquaculture, Agricultural University of Athens, Greece. eftychia.xylouri@yahoo.gr
authors.forename: Maria
authors.initials: M
authors.lastname: Bountouri
authors.forename: Eirini
authors.initials: E
authors.lastname: Fragkiadaki
authors.forename: Vasileios
authors.initials: V
authors.lastname: Ntafis
authors.forename: Theo
authors.initials: T
authors.lastname: Kanellos
authors.forename: Eftychia
authors.initials: E
authors.lastname: Xylouri
mesh_terms: D000818:Animals; D002460:Cell Line; D016000:Cluster Analysis; D004285:Dogs; D006115:Greece; D006385:Hemagglutination Inhibition Tests; D006734:Horse Diseases / Q000821:virology*; D006736:Horses / Q000821:virology*; D053123:Influenza A Virus, H3N8 Subtype / Q000235:genetics / Q000302:isolation & purification*; D008969:Molecular Sequence Data; D009297:Nasal Mucosa / Q000821:virology; D009976:Orthomyxoviridae Infections / Q000821:virology*; D010802:Phylogeny; D012367:RNA, Viral / Q000235:genetics; D016865:Reassortant Viruses / Q000235:genetics / Q000302:isolation & purification*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014776:Virus Cultivation
chemical_list: D012367:RNA, Viral