A Comprehensive Review on Equine Influenza Virus: Etiology, Epidemiology, Pathobiology, Advances in Developing Diagnostics, Vaccines, and Control Strategies

Abstract

Among all the emerging and re-emerging animal diseases, influenza group is the prototype member associated with severe respiratory infections in wide host species. Wherein, Equine influenza (EI) is the main cause of respiratory illness in equines across globe and is caused by equine influenza A virus (EIV-A) which has impacted the equine industry internationally due to high morbidity and marginal morality. The virus transmits easily by direct contact and inhalation making its spread global and leaving only limited areas untouched. Hitherto reports confirm that this virus crosses the species barriers and found to affect canines and few other animal species (cat and camel). EIV is continuously evolving with changes at the amino acid level wreaking the control program a tedious task. Until now, no natural EI origin infections have been reported explicitly in humans. Recent advances in the diagnostics have led to efficient surveillance and rapid detection of EIV infections at the onset of outbreaks. Incessant surveillance programs will aid in opting a better control strategy for this virus by updating the circulating vaccine strains. Recurrent vaccination failures against this virus due to antigenic drift and shift have been disappointing, however better understanding of the virus pathogenesis would make it easier to design effective vaccines predominantly targeting the conserved epitopes (HA glycoprotein). Additionally, the cold adapted and canarypox vectored vaccines are proving effective in ceasing the severity of disease. Furthermore, better understanding of its genetics and molecular biology will help in estimating the rate of evolution and occurrence of pandemics in future. Here, we highlight the advances occurred in understanding the etiology, epidemiology and pathobiology of EIV and a special focus is on designing and developing effective diagnostics, vaccines and control strategies for mitigating the emerging menace by EIV.

Success and Limitation of Equine Influenza Vaccination: The First Incursion in a Decade of a Florida Clade 1 Equine Influenza Virus that Shakes Protection Despite High Vaccine Coverage

“…The scale, number and duration of this epidemic had not been experienced in Europe since the late 1970s and 1980s. Sequencing results revealed that H3N8 EIV strains at the origin of the 2018-2019 French outbreaks (and EI outbreaks in other European countries, OIE ESP communication) belong to the FC1 sub-lineage, which was not isolated in France since 2009 [13] and was usually circulating in North and South Americas [17,20,32]. While several amino acids mutation were identified in the HA, results from the hemagglutination inhibition assay using mono-specific ferret sera and the associated antigenic cartography analyses indicate that FC1 EIV strains the origin of the 2018-2019 EI outbreaks were still antigenically closely related to the recommended FC1 EIV strains for inclusion in EI vaccine [33].…”

<p>Immunoinformatics and Vaccine Development: An Overview</p>

“…Influenza viruses are able to thrive for a long while in a given human population. 111,112 The virus has a high mutation rate such that a once effective vaccine can easily lose efficacy. Antigenic variability is only one of the evidences of phenotypic variation in the biology of the Influenza virus.…”

Animal influenza virus infections in humans: A commentary

“…Equine influenza viruses (EIVs) are an important cause of respiratory tract disease in horses, chiefly caused by the H3N8 influenza A subtype (Singh et al, 2018). Before vaccines were developed, EIV outbreaks in equine populations were very common and had a case fatality as high as 20% (Sack et al, 2017).…”