A Review on Equine Influenza from a Human Influenza Perspective

Abstract

Influenza A viruses (IAVs) have a main natural reservoir in wild birds. IAVs are highly contagious, continually evolve, and have a wide host range that includes various mammalian species including horses, pigs, and humans. Furthering our understanding of host-pathogen interactions and cross-species transmissions is therefore essential. This review focuses on what is known regarding equine influenza virus (EIV) virology, pathogenesis, immune responses, clinical aspects, epidemiology (including factors contributing to local, national, and international transmission), surveillance, and preventive measures such as vaccines. We compare EIV and human influenza viruses and discuss parallels that can be drawn between them. We highlight differences in evolutionary rates between EIV and human IAVs, their impact on antigenic drift, and vaccine strain updates. We also describe the approaches used for the control of equine influenza (EI), which originated from those used in the human field, including surveillance networks and virological analysis methods. Finally, as vaccination in both species remains the cornerstone of disease mitigation, vaccine technologies and vaccination strategies against influenza in horses and humans are compared and discussed.

A multilocus perspective on the evolutionary dynamics of multistrain pathogens

“…Our model would therefore predict that, all else being equal, EIV should be less genotypically diverse than IAV. Interestingly, EIV can be roughly divided into three antigenic clusters [56], whereas IAV consists of 11 antigenic clusters [57] (see also [58]). Of course, EIV and IAV differ with respect to other properties (e.g., IAV undergoes more rapid antigenic drift [58]); testing how the shape of the function controlling antigen-specific cross-protections limits genotypic diversity and constrains evolutionary dynamics warrants further work.…”

Equine Influenza Virus: An Old Known Enemy in the Americas

“…Differences between EIV and human influenza virus sialic acid receptors may act as a restriction factor for the interspecies transmission from equine to humans and for the efficient human-to-human spread of EIV [ 55 ]. However, in addition to sialic acid, other viral and host genes could be responsible for influencing host range and interspecies jumps that still need to be clarified [ 56 ].…”

“…Some of these risk factors have been extensively reported for IAV infections in humans, which are mainly related to international travel and outbreaks appearing through contact with fomites or microdroplets from infected individuals [ 56 ].…”

“…The latter is recommended by the WOAH because it includes the representative viruses of both Clades 1 and 2 of the Florida sublineage [ 69 ]. In addition, the WOAH Expert Surveillance Panel on Equine Influenza Vaccine Composition recommends updating the vaccines that are sold; however, it is difficult due to the time and cost that this process implies for the commercial market [ 56 ]. Currently, other types of vaccines have been developed, such as adjuvanted subunits and genomic vaccines [ 6 , 56 ].…”

“…In addition, the WOAH Expert Surveillance Panel on Equine Influenza Vaccine Composition recommends updating the vaccines that are sold; however, it is difficult due to the time and cost that this process implies for the commercial market [ 56 ]. Currently, other types of vaccines have been developed, such as adjuvanted subunits and genomic vaccines [ 6 , 56 ]. In the development of new vaccines, it is important to keep in mind the type of adjuvant employed because it generates a better immune response, even similar to the immune response developed by a new field strain, in addition to generating a rapid decrease in clinical signs [ 70 ].…”