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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. CONCLUSION: 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.

SUBMITTER: Bountouri M

PROVIDER: S-EPMC3158125 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature

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Phylogenetic and molecular characterization of equine H3N8 influenza viruses from Greece (2003 and 2007): evidence for reassortment between evolutionary lineages.

Bountouri Maria M Fragkiadaki Eirini E Ntafis Vasileios V Kanellos Theo T Xylouri Eftychia E

Virology journal 20110714

<h4>Background</h4>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.<h4>Methods</h4>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 ...[more]

PMID: 21756308

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Project description:Equine influenza viruses (EIV) are a major cause of acute respiratory disease in horses worldwide and occasionally also affect vaccinated animals. Like other influenza A viruses, they undergo antigenic drift, highlighting the importance of both surveillance and virus characterisation in order for vaccine strains to be kept up to date. The aim of the work reported here was to monitor the genetic and antigenic changes occurring in EIV circulating in the UK from 2013 to 2015 and to identify any evidence of vaccine breakdown in the field. Virus isolation, reverse transcription polymerase chain reaction (RT-PCR) and sequencing were performed on EIV-positive nasopharyngeal swab samples submitted to the Diagnostic Laboratory Services at the Animal Health Trust (AHT). Phylogenetic analyses were completed for the haemagglutinin-1 (HA1) and neuraminidase (NA) genes using PhyML and amino acid sequences compared against the current World Organisation for Animal Health (OIE)-recommended Florida clade 2 vaccine strain. Substitutions between the new isolates and the vaccine strain were mapped onto the three-dimensional structure protein structures using PyMol. Antigenic analyses were carried out by haemagglutination inhibition assay using a panel of post-infection ferret antisera. Sixty-nine outbreaks of equine influenza in the UK were reported by the AHT between January 2013 and December 2015. Forty-seven viruses were successfully isolated in eggs from 41 of the outbreaks. Only three cases of vaccine breakdown were identified and in each case the vaccine used contained a virus antigen not currently recommended for equine influenza vaccines. Nucleotide sequencing of the HA and NA genes revealed that all of the viruses belonged to the Florida clade 2 sub-lineage of H3N8 EIV. Phylogenetic and sequence analyses showed that the two sub-populations, previously identified within clade 2, continued to circulate and had accrued further amino acid substitutions. Antigenic characterisation using post-infection ferret antisera in haemagglutination inhibition assays however, failed to detect any marked antigenic differences between the isolates. These findings show that Florida clade 2 EIV continue to circulate in the UK and support the current OIE recommendation to include an example of Florida clade 2 in vaccines.

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Phylogenetic and molecular characterization of equine H3N8 influenza viruses from Greece (2003 and 2007): evidence for reassortment between evolutionary lineages.

Publications

Phylogenetic and molecular characterization of equine H3N8 influenza viruses from Greece (2003 and 2007): evidence for reassortment between evolutionary lineages.

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