Characterisation of equine influenza isolates from the 1987 epizootic in India by nucleotide sequencing of the HA1 gene

Epidemiology of equine influenza in the Maghreb area

Equine influenza (EI) is one of the most contagious respiratory infections in horses, donkeys and mules, caused by equine influenza A virus (EIV). It remains a disease with a strong economic stake for the equine industry. This review focuses on the epidemiological situation of EIV in the Maghreb area, which includes Algeria, Morocco and Tunisia. There is serological evidence for extensive circulation of EIV in the Maghreb area since the early 1970s, but reports of detailed investigation of outbreaks are scarce with no documented isolation or molecular characterization of EIV from Tunisia. Isolates of EIV were obtained from outbreaks in Algeria in 1971/1972 and 2011. Similarly, in Morocco, isolates were obtained from outbreaks in 1997 and 2004. The viruses isolated in 2004 showed evidence of 'evolutionary stasis', with haemagglutinin and non-structural protein 1 sequences most similar to those of viruses isolated decades earlier. In conclusion, effective surveillance of equids in the Maghreb region, where there is potential for virus re-emergence, should be encouraged.

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

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.

Characterisation of three equine influenza A H3N8 viruses from Germany (2000 and 2002): evidence for frozen evolution

Reported here are the results of antigenic and genetic characterisation of equine influenza strains causing local outbreaks reported to the Equine Diagnostic Centre in Berlin, Germany. In 2000, equine influenza virus was detected in a nasal swab from a non-vaccinated horse using a rapid diagnostic kit, but was not successfully isolated. Partial direct sequencing of the haemagglutinin (HA1) gene, indicated that the virus was a European lineage H3N8 subtype strain representative of strains isolated in several European countries during 2000. In 2002, two equine influenza viruses were isolated from nasal swabs both taken from unvaccinated horses with acute respiratory symptoms housed at the same stables. Antigenic characterisation using a panel of ferret antisera suggested that these isolates also belonged to the European lineage of H3N8 viruses. Analysis of deduced HA1 amino acid sequences confirmed that the HA1 of both isolates were identical and belonged to the European lineage. However, from phylogenetic analysis, both strains appeared to be more closely related to viruses isolated between 1989 and 1995 than to viruses isolated more recently in Europe. These results suggested that viruses with fewer changes than those on the main evolutionary lineage may continue to circulate. The importance of expanding current equine influenza surveillance efforts is emphasised.

Lower airway diseases of the adult horse

Lower airway problems of the adult horse are commonly encountered by the practitioner. Particularly susceptible populations include horses transported for any significant distance and young horses grouped together for training and/or competition. This article presents some of the commonly encountered problems of this patient population, including bacterial pneumonia/pleuropneumonia and influenza, and some uncommon ones, including pulmonary edema, pneumothorax/hemothorax, and acuterespiratory distress syndrome. Information is presented that should allow the practitioner to diagnose these problems accurately and initiate rational treatment plans.

Evidence for evolutionary stasis and genetic drift by genetic analysis of two equine influenza H3 viruses isolated in France

The amino acid sequences of the HA(1) portion of the haemagglutinin of two equine A(H3N8) influenza viruses isolated in France in 1993 and 1998 were analysed to determine their evolutionary relationship with 51 other HA(1) amino acid sequences available in databanks. Our data show that the French strain isolated in 1993 belongs to a group of phylogenetically related viruses branched on the main trunk, illustrating the main lineage of evolution of the equine-2 H3 sequences before its split into two distinct lineages in the late 1980s. By contrast, the 1998 French isolate appears to belong to the more recent 'Eurasian' lineage. These data suggest that equine-2 strains antigenically related to old prototype viruses may cocirculate with the more recent 'Eurasian' and 'American' lineages. In conclusion, it may be necessary to include both strains representative of recent equine influenza variants and an older prototype strain in the current equine influenza vaccines.

Genetic and antigenic analysis of an equine influenza H 3 isolate from the 1989 epidemic

The haemagglutinin (HA) gene from the equine influenza H3N8 isolate Suffolk/89 has been cloned by reverse transcription and polymerase chain reaction amplification. The nucleotide sequence of the HA gene was determined from two independently cloned copies of the gene and was found to be most closely related to recent American isolates supporting the idea that most isolates of equine H3N8 are evolving as a single lineage. When the predicted amino acid sequence of the Suffolk/89 HA was examined, changes had taken place in at least four of the major antigenic sites, A, B, C, and D when compared to the sequences of the isolates used in the current vaccines (Miami/63 and Fontainebleau/79). Surprisingly, when the Suffolk/89 isolate was tested in haemagglutination inhibition (HI) assays with a panel of six mouse monoclonal antibodies, no differences were observed between the Suffolk/89 and the Fontainebleau/79 isolates, suggesting that this panel of monoclonal antibodies may recognise a limited subset of the major antigenic sites. Three anti-HA horse heterohybridoma monoclonals were able to distinguish between the Suffolk/89 and Fontainebleau/79 viruses, demonstrating that the horse does recognise these isolates as being antigenically different. The results of the work suggest that the isolates used in current equine influenza vaccines may need updating.