Special Issue "Equine Influenza"

A special issue of Pathogens (ISSN 2076-0817).

Deadline for manuscript submissions: closed (2 May 2016).

Special Issue Editor

Assoc. Prof. Janet M. Daly
Website
Guest Editor
School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington Campus, Sutton Bonington, Leicestershire, LE12 5RD, UK
Interests: epidemiology and evolution of viruses; development and testing of viral vaccines, antivirals and diagnostics; science communication

Special Issue Information

Dear Colleagues,

Equine influenza is a highly contagious disease currently caused by influenza A viruses of the H3N8 subtype. In common with human influenza, the disease is characterized by fever, cough and nasal discharge. Infected individuals usually recover within around two weeks, although disease can be more severe in some, due to secondary bacterial infection or as a result of infection with more pathogenic strains. Typical of emergent viruses, in recent years, equine influenza virus has caused an economically devastating outbreak in Australia (previously free of the virus) and was transmitted to a new host, becoming endemic in dogs in the USA.

Possibly because it is not a zoonotic pathogen, equine influenza is sometimes referred to as a ‘neglected’ influenza virus. In the past, when horses were relied on more widely as draft animals, outbreaks of equine influenza were crippling to economies. Today, the disease is largely a concern for the horseracing and competition industries in developed countries. Despite its ‘neglected’ status, there is a plethora of vaccine formulations available to combat equine influenza, and the many parallels with human disease suggest that the horse provides a good model for furthering our understanding of influenza.

Dr. Janet M. Daly
Guest Editor

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Keywords

  • Equine influenza
  • Vaccines
  • Epidemiology
  • Transmission
  • Pathogenicity

Published Papers (8 papers)

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Research

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Open AccessArticle
Evolution and Divergence of H3N8 Equine Influenza Viruses Circulating in the United Kingdom from 2013 to 2015
Pathogens 2017, 6(1), 6; https://doi.org/10.3390/pathogens6010006 - 08 Feb 2017
Cited by 18
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Equine Influenza)
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Open AccessArticle
The Optimisation of Pseudotyped Viruses for the Characterisation of Immune Responses to Equine Influenza Virus
Pathogens 2016, 5(4), 68; https://doi.org/10.3390/pathogens5040068 - 15 Dec 2016
Cited by 1
Abstract
Pseudotyped viruses (PVs) produced by co-transfecting cells with plasmids expressing lentiviral core proteins and viral envelope proteins are potentially powerful tools for studying various aspects of equine influenza virus (EIV) biology. The aim of this study was to optimise production of equine influenza [...] Read more.
Pseudotyped viruses (PVs) produced by co-transfecting cells with plasmids expressing lentiviral core proteins and viral envelope proteins are potentially powerful tools for studying various aspects of equine influenza virus (EIV) biology. The aim of this study was to optimise production of equine influenza PVs. Co-transfection of the HAT protease to activate the haemagglutinin (HA) yielded a higher titre PV than TMPRSS2 with the HA from A/equine/Richmond/1/2007 (H3N8), whereas for A/equine/Newmarket/79 (H3N8), both proteases resulted in equivalent titres. TMPRSS4 was ineffective with the HA of either strain. There was also an inverse relationship between the amount of protease-expression plasmids and the PV titre obtained. Interestingly, the PV titre obtained by co-transfection of a plasmid encoding the cognate N8 NA was not as high as that generated by the addition of exogenous neuraminidase (NA) from Clostridium perfringens to allow the release of nascent PV particles. Finally, initial characterisation of the reliability of PV neutralisation tests (PVNTs) demonstrated good intra-laboratory repeatability. In conclusion, we have demonstrated that equine influenza PV production can be readily optimised to provide a flexible tool for studying EIV. Full article
(This article belongs to the Special Issue Equine Influenza)
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Open AccessFeature PaperArticle
Molecular Epidemiology and Spatio-Temporal Dynamics of the H3N8 Equine Influenza Virus in South America
Pathogens 2016, 5(4), 61; https://doi.org/10.3390/pathogens5040061 - 16 Oct 2016
Cited by 7
Abstract
Equine influenza virus (EIV) is considered the most important respiratory pathogen of horses as outbreaks of the disease lead to substantial economic losses. The H3N8 EIV has caused respiratory disease in horses across the world, including South American countries. Nucleotide and deduced amino [...] Read more.
Equine influenza virus (EIV) is considered the most important respiratory pathogen of horses as outbreaks of the disease lead to substantial economic losses. The H3N8 EIV has caused respiratory disease in horses across the world, including South American countries. Nucleotide and deduced amino acid sequences for the complete haemagglutinin gene of the H3N8 EIV detected in South America since 1963 were analyzed. Phylogenetic and Bayesian coalescent analyses were carried out to study the origin, the time of the most recent common ancestors (tMRCA), the demographic and the phylogeographic patterns of the H3N8 EIV. The phylogenetic analysis demonstrated that the H3N8 EIV detected in South America grouped in 5 well-supported monophyletic clades, each associated with strains of different origins. The tMRCA estimated for each group suggested that the virus was circulating in North America at least one year before its effective circulation in the South American population. Phylogenetic and coalescent analyses revealed a polyphyletic behavior of the viruses causing the outbreaks in South America between 1963 and 2012, possibly due to the introduction of at least 4 different EIVs through the international movement of horses. In addition, phylodynamic analysis suggested South America as the starting point of the spread of the H3N8 EIV in 1963 and showed migration links from the United States to South America in the subsequent EIV irruptions. Further, an increase in the relative genetic diversity was observed between 2006 and 2007 and a subsequent decline since 2009, probably due to the co-circulation of different lineages and as a result of the incorporation of the Florida clade 2 strain in vaccines, respectively. The observed data highlight the importance of epidemiological surveillance and the implementation of appropriate quarantine procedures to prevent outbreaks of the disease. Full article
(This article belongs to the Special Issue Equine Influenza)
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Open AccessArticle
Retrospective Analysis of the Equine Influenza Virus A/Equine/Kirgizia/26/1974 (H7N7) Isolated in Central Asia
Pathogens 2016, 5(3), 55; https://doi.org/10.3390/pathogens5030055 - 10 Aug 2016
Cited by 2
Abstract
A retrospective phylogenetic characterization of the hemagglutinin, neuraminidase and nucleoprotein genes of equine influenza virus A/equine/Kirgizia/26/1974 (H7N7) which caused an outbreak in Kirgizia (a former Soviet Union republic, now Kyrgyzstan) in 1977 was conducted. It was defined that it was closely related to [...] Read more.
A retrospective phylogenetic characterization of the hemagglutinin, neuraminidase and nucleoprotein genes of equine influenza virus A/equine/Kirgizia/26/1974 (H7N7) which caused an outbreak in Kirgizia (a former Soviet Union republic, now Kyrgyzstan) in 1977 was conducted. It was defined that it was closely related to the strain London/1973 isolated in Europe and it shared a maximum nucleotide sequence identity at 99% with it. This Central Asian equine influenza virus isolate did not have any specific genetic signatures and can be considered as an epizootic strain of 1974 that spread in Europe. The absence of antibodies to this subtype EI virus (EIV) in recent research confirms its disappearance as of the 1990s when the antibodies were last found in unvaccinated horses. Full article
(This article belongs to the Special Issue Equine Influenza)
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Review

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Open AccessReview
How to Meet the Last OIE Expert Surveillance Panel Recommendations on Equine Influenza (EI) Vaccine Composition: A Review of the Process Required for the Recombinant Canarypox-Based EI Vaccine
Pathogens 2016, 5(4), 64; https://doi.org/10.3390/pathogens5040064 - 25 Nov 2016
Cited by 11
Abstract
Vaccination is highly effective to prevent, control, and limit the impact of equine influenza (EI), a major respiratory disease of horses. However, EI vaccines should contain relevant equine influenza virus (EIV) strains for optimal protection. The OIE expert surveillance panel annually reviews EIV [...] Read more.
Vaccination is highly effective to prevent, control, and limit the impact of equine influenza (EI), a major respiratory disease of horses. However, EI vaccines should contain relevant equine influenza virus (EIV) strains for optimal protection. The OIE expert surveillance panel annually reviews EIV evolution and, since 2010, the use of Florida clade 1 and 2 sub-lineages representative vaccine strains is recommended. This report summarises the development process of a fully- updated recombinant canarypox-based EI vaccine in order to meet the last OIE recommendations, including the vaccine mode of action, production steps and schedule. The EI vaccine ProteqFlu contains 2 recombinant canarypox viruses expressing the haemagglutinin of the A/equine/Ohio/03 and A/equine/Richmond/1/07 isolates (Florida clade 1 and 2 sub-lineages, respectively). The updated EI vaccine was tested for efficacy against the representative Florida clade 2 EIV strain A/equine/Richmond/1/07 in the Welsh mountain pony model. Protective antibody response, clinical signs of disease and virus shedding were compared with unvaccinated control ponies. Significant protection was measured in vaccinated ponies, which supports the vaccine registration. The recombinant canarypox-based EI vaccine was the first fully updated EI vaccine available in the EU, which will help to minimise the increasing risk of vaccine breakdown due to constant EIV evolution through antigenic drift. Full article
(This article belongs to the Special Issue Equine Influenza)
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Open AccessReview
The Influenza NS1 Protein: What Do We Know in Equine Influenza Virus Pathogenesis?
Pathogens 2016, 5(3), 57; https://doi.org/10.3390/pathogens5030057 - 31 Aug 2016
Cited by 4
Abstract
Equine influenza virus remains a serious health and potential economic problem throughout most parts of the world, despite intensive vaccination programs in some horse populations. The influenza non-structural protein 1 (NS1) has multiple functions involved in the regulation of several cellular and viral [...] Read more.
Equine influenza virus remains a serious health and potential economic problem throughout most parts of the world, despite intensive vaccination programs in some horse populations. The influenza non-structural protein 1 (NS1) has multiple functions involved in the regulation of several cellular and viral processes during influenza infection. We review the strategies that NS1 uses to facilitate virus replication and inhibit antiviral responses in the host, including sequestering of double-stranded RNA, direct modulation of protein kinase R activity and inhibition of transcription and translation of host antiviral response genes such as type I interferon. Details are provided regarding what it is known about NS1 in equine influenza, especially concerning C-terminal truncation. Further research is needed to determine the role of NS1 in equine influenza infection, which will help to understand the pathophysiology of complicated cases related to cytokine imbalance and secondary bacterial infection, and to investigate new therapeutic and vaccination strategies. Full article
(This article belongs to the Special Issue Equine Influenza)
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Open AccessReview
A Review of Evidence that Equine Influenza Viruses Are Zoonotic
Pathogens 2016, 5(3), 50; https://doi.org/10.3390/pathogens5030050 - 12 Jul 2016
Cited by 13
Abstract
Among scientists, there exist mixed opinions whether equine influenza viruses infect man. In this report, we summarize a 2016 systematic and comprehensive review of the English, Chinese, and Mongolian scientific literature regarding evidence for equine influenza virus infections in man. Searches of PubMed, [...] Read more.
Among scientists, there exist mixed opinions whether equine influenza viruses infect man. In this report, we summarize a 2016 systematic and comprehensive review of the English, Chinese, and Mongolian scientific literature regarding evidence for equine influenza virus infections in man. Searches of PubMed, Web of Knowledge, ProQuest, CNKI, Chongqing VIP Database, Wanfang Data and MongolMed yielded 2831 articles, of which 16 met the inclusion criteria for this review. Considering these 16 publications, there was considerable experimental and observational evidence that at least H3N8 equine influenza viruses have occasionally infected man. In this review we summarize the most salient scientific reports. Full article
(This article belongs to the Special Issue Equine Influenza)
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Open AccessReview
The Use of a Recombinant Canarypox-Based Equine Influenza Vaccine during the 2007 Australian Outbreak: A Systematic Review and Summary
Pathogens 2016, 5(2), 42; https://doi.org/10.3390/pathogens5020042 - 10 Jun 2016
Cited by 15
Abstract
In 2007, Australia experienced the most extensive equine influenza outbreak observed in recent years. Extraordinary measures were rapidly implemented in order to control and prevent the spread of this highly contagious disease. The control strategy involved stringent movement restriction and disease surveillance, seconded [...] Read more.
In 2007, Australia experienced the most extensive equine influenza outbreak observed in recent years. Extraordinary measures were rapidly implemented in order to control and prevent the spread of this highly contagious disease. The control strategy involved stringent movement restriction and disease surveillance, seconded by emergency post-outbreak vaccination strategies. Sixteen months after the first case and 12 months following the last reported case, Australia regained its equine influenza-free OIE status. This systematic review reports and summarises information relating to the implementation of emergency vaccination during the 2007 Australian equine influenza outbreak, including the choice of vaccine and implementation strategies. Full article
(This article belongs to the Special Issue Equine Influenza)
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