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Multifocal outbreak of equine influenza in vaccinated horses in Argentina in 2018: Epidemiological aspects and molecular characterisation of the involved virus strains

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  • Multifocal outbreak of equine influenza in vaccinated horses in Argentina in 2018: Epidemiological aspects and molecular characterisation of the involved virus strains

    Equine Vet J. 2019 Sep 8. doi: 10.1111/evj.13176. [Epub ahead of print]
    Multifocal outbreak of equine influenza in vaccinated horses in Argentina in 2018: Epidemiological aspects and molecular characterisation of the involved virus strains.

    Olguin-Perglione C1, Vissani MA1,2, Alamos F1, Tordoya MS1, Barrandeguy M1,2.
    Author information

    1 Instituto Nacional de Tecnología Agropecuaria (INTA), Instituto de Virología, Buenos Aires, Argentina. 2 Escuela de Veterinaria, Universidad del Salvador, Champagnat, 1599, Ruta Panamericana km 54.5 (B1630AHU), Pilar, Buenos Aires, Argentina.

    Abstract

    BACKGROUND:

    Equine influenza is an important cause of respiratory disease of horses worldwide. The equine influenza virus (EIV) undergoes antigenic drift through the accumulation of amino acid substitutions in the viral proteins, which may lead to vaccine breakdown.
    OBJECTIVES:

    To describe the epidemiological findings and the molecular characteristics of the EIV detected during the multifocal outbreak that occurred in Argentina between March and July 2018 and evidence a vaccine breakdown.
    STUDY DESIGN:

    Observational, descriptive study.
    METHODS:

    Virus was detected in nasopharyngeal swabs by real-time RT-PCR. Nucleotide and deduced amino acid sequences of the haemagglutinin (HA) and neuraminidase (NA) genes were obtained from EIV positive nasopharyngeal swabs, and phylogenetic analysis was undertaken. Amino acid sequences were compared against the current World Organisation for Animal Health (OIE)-recommended Florida clade 1 vaccine strain and strain components of vaccines used in Argentina. Serum samples were tested by haemagglutination inhibition test.
    RESULTS:

    EIV infection was confirmed by real-time RT-PCR and serological testing. The phylogenetic analysis of the HA and NA genes revealed all the EIV identified during the outbreak belong to the H3N8 subtype, Florida clade 1. Multiple amino acid changes, some of them at antigenic sites, were observed in the currently circulating virus when compared with the strains included in the most commonly used vaccine in Argentina. Seventy-six percent of the affected horses had been vaccinated with this vaccine, suggesting the occurrence of vaccine breakdown.
    MAIN LIMITATIONS:

    The study does not include antigenic characterisation and full genome sequencing of Argentinian strains, that could provide additional information.
    CONCLUSIONS:

    The occurrence of this multifocal equine influenza outbreak in regularly vaccinated horses is field evidence of vaccine breakdown, reinforcing the necessity of keeping vaccine strains updated according to OIE recommendations. It too underlines the importance of the implementation of appropriate quarantine measures and restriction of horse movement in the face of disease.
    © 2019 EVJ Ltd.


    KEYWORDS:

    Florida clade 1; H3N8; South America; haemagglutinin; horse; neuraminidase

    PMID: 31494962 DOI: 10.1111/evj.13176
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