ABSTRACT
Equine influenza viruses are a major cause of respiratory disease in horses worldwide and undergo antigenic drift. Several outbreaks of equine influenza occurred worldwide during 2010-2012, including in vaccinated animals, highlighting the importance of surveillance and virus characterisation. Virus isolates were characterised from more than 20 outbreaks over a 3-year period, including strains from the UK, Dubai, Germany and the USA. The haemagglutinin-1 (HA1) sequence of all isolates was determined and compared with OIE-recommended vaccine strains. Viruses from Florida clades 1 and 2 showed continued divergence from each other compared with 2009 isolates. The antigenic inter-relationships among viruses were determined using a haemagglutination-inhibition (HI) assay with ferret antisera and visualised using antigenic cartography. All European isolates belonged to Florida clade 2, all those from the USA belonged to Florida clade 1. Two subpopulations of clade 2 viruses were isolated, with either substitution A144V or I179V. Isolates from Dubai, obtained from horses shipped from Uruguay, belonged to Florida clade 1 and were similar to viruses isolated in the USA the previous year. The neuraminidase (NA) sequence of representative strains from 2007 and 2009 to 2012 was also determined and compared with that of earlier isolates dating back to 1963. Multiple changes were observed at the amino acid level and clear distinctions could be made between viruses belonging to Florida clade 1 and clade 2.
Subject(s)
Horse Diseases/virology , Influenza A Virus, H3N8 Subtype/classification , Influenza A Virus, H3N8 Subtype/genetics , Orthomyxoviridae Infections/veterinary , Amino Acid Sequence , Animals , Europe , Hemagglutinins, Viral/genetics , Horse Diseases/epidemiology , Horses , Models, Molecular , Molecular Sequence Data , Neuraminidase/chemistry , Neuraminidase/genetics , Orthomyxoviridae Infections/virology , Phylogeny , Population Surveillance , Protein Structure, Tertiary , Sequence Alignment , United Arab Emirates , United StatesABSTRACT
Equine influenza virus (EIV) surveillance is important in the management of equine influenza. It provides data on circulating and newly emerging strains for vaccine strain selection. To this end, antigenic characterisation by haemaggluttination inhibition (HI) assay and phylogenetic analysis was carried out on 28 EIV strains isolated in North America and Europe during 2006 and 2007. In the UK, 20 viruses were isolated from 28 nasopharyngeal swabs that tested positive by enzyme-linked immunosorbent assay. All except two of the UK viruses were characterised as members of the Florida sublineage with similarity to A/eq/Newmarket/5/03 (clade 2). One isolate, A/eq/Cheshire/1/06, was characterised as an American lineage strain similar to viruses isolated up to 10 years earlier. A second isolate, A/eq/Lincolnshire/1/07 was characterised as a member of the Florida sublineage (clade 1) with similarity to A/eq/Wisconsin/03. Furthermore, A/eq/Lincolnshire/1/06 was a member of the Florida sublineage (clade 2) by haemagglutinin (HA) gene sequence, but appeared to be a member of the Eurasian lineage by the non-structural gene (NS) sequence suggesting that reassortment had occurred. A/eq/Switzerland/P112/07 was characterised as a member of the Eurasian lineage, the first time since 2005 that isolation of a virus from this lineage has been reported. Seven viruses from North America were classified as members of the Florida sublineage (clade 1), similar to A/eq/Wisconsin/03. In conclusion, a variety of antigenically distinct EIVs continue to circulate worldwide. Florida sublineage clade 1 viruses appear to predominate in North America, clade 2 viruses in Europe.
Subject(s)
Genetic Variation , Horse Diseases/virology , Influenza A Virus, H3N8 Subtype/genetics , Orthomyxoviridae Infections/veterinary , Amino Acid Sequence , Animals , Antibodies, Viral/immunology , Chickens/virology , Enzyme-Linked Immunosorbent Assay , Erythrocytes/virology , Europe , Genes, Viral , Horses , Influenza A Virus, H3N8 Subtype/classification , Influenza A Virus, H3N8 Subtype/isolation & purification , Lung Diseases/veterinary , Lung Diseases/virology , Nasopharynx/virology , North America , Polymerase Chain Reaction , Sequence Alignment , Viral Nonstructural Proteins/geneticsABSTRACT
We retrospectively demonstrated that an outbreak of severe respiratory disease in a pack of English foxhounds in the United Kingdom in September 2002 was caused by an equine influenza A virus (H3N8). We also demonstrated that canine respiratory tissue possesses the relevant receptors for infection with equine influenza virus.
