Development of a surveillance scheme for equine influenza in the UK and characterisation of viruses isolated in Europe, Dubai and the USA from 2010–2012

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 interrelationships 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. Revision note VETMIC-D-13-8580Authors' response to reviewer comments: We agree with the reviewer that there are two topics here. However, we also believe that they are closely linked and that the increase in diagnostic sample submission should be sufficient justification to include the strategies used to encourage practitioners to submit nasal swabs. In response, we have therefore deleted surveillance data from the results & discussion, but retained the approaches used in the method section, for reference purposes.The scheme only relates to equine influenza as the financial support we have from the HBLB only covers 'flu. This is considered the major threat to horse racing and breeding in the UK, due to its rapid spread in an unprotected population.The 'free' surveillance scheme allows us to characterise samples sent from other countries as well as the UK. We believe that for countries where funding could potentially be sought, this scheme provides examples of low-cost methods that can be used to improve surveillance & sample submission, such as Twitter. We fully accept that this isn't possible in all countries. The isolate characterization data is certainly of value in monitoring the changes in EIV. What is disappointing is that all of the work done so far does not seem able to predict when a new vaccine will be needed. The antigenic mapping and serology tests tell us that changes are occurring and where in the HA and NA, but little about the efficacy of the current vaccines. Field data still seems most reliable. On...

Epidemiological and virological findings during multiple outbreaks of equine influenza in South America in 2012

“…Moreover, 3 of 18 endurance horses, which were exported from Uruguay to Dubai on 30th May 2012, exhibited fever and respiratory clinical signs 6 days post‐arrival at quarantine. Equine influenza virus was isolated from nasopharyngeal swabs collected from these horses and genetically characterised 19. Our study provides molecular support for the hypothesis that these horses were infected prior to export as the HA1 gene of the virus detected in Maroñas had 100% amino acid sequence identity to the virus isolated in the Dubai quarantine facility.…”

“…All viruses identified in South America 2012 had an additional substitution at the predicted peptide signal sequence, K‐14T or K‐14A, when compared with the Florida clade 1 reference strain. The substitution K‐14T occurred in A/eq/San Isidro/E‐2357/2012, A/eq/Areco/E‐2397‐3/2012, A/eq/Esquel/E‐3146‐1/2012 and A/eq/La Plata/E‐2346‐1/2012 and in other strains recently circulating in Europe 11, 18, 19, 29. The substitution K‐14A, derived from the nucleotide change in the position 33 (A33G), was present in A/eq/Maroñas/E‐1918‐1/2012, A/eq/Palermo/E‐2345‐1/2012 and A/eq/La Plata/E‐2346‐2/2012 and to the authors knowledge has not previously been reported.…”

“…Our study provides molecular support for the hypothesis that these horses were infected prior to export as the HA1 gene of the virus detected in Maroñas had 100% amino acid sequence identity to the virus isolated in the Dubai quarantine facility. The imported horses had received a primary course of two doses of vaccine in accordance with the manufacturer's recommendations 19. The occurrence of EI in these horses is notable, as it illustrates the risk of global virus spread through international movement of vaccinated horses.…”

“…Subsequent evolution within the Florida sublineage has resulted in the emergence of two distinct clades, designated as Florida clade 1 and Florida clade 2 11, 12. Florida clade 1 viruses are endemic in the USA but have also caused outbreaks in South Africa,13 Japan,14 Australia 15 and Europe 11, 16, 17, 18, 19. Florida clade 2 viruses have predominated in Europe but have also been the cause of major outbreaks of EI in China,20 Mongolia 21 and India 22…”

Concurrent vaccination against equine influenza and equine herpesvirus – a practical approach

“…Epidemiological investigations of acute respiratory disease have confirmed that equine influenza virus (EIV) and equine herpesvirus 1 and 4 (EHV‐1/4) are important causes of both clinical and subclinical infection among young horses in racing yards and stud farms, and those returning from equestrian events 1, 2, 3, 4, 5. Disease and suboptimal performance following infection with these viruses can result in significant financial loss.…”