Instituto de Virología, Instituto Nacional de Tecnología Agropecuaria (INTA), Hurlingham, Buenos Aires, Argentina.
Escuela de Veterinaria, Universidad del Salvador, Pilar, Buenos Aires, Argentina.
Equine Vet J. 2020 May;52(3):420-427. doi: 10.1111/evj.13176. Epub 2019 Oct 4.
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.
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.
Observational, descriptive study.
Virus was detected in nasopharyngeal swabs using real-time reverse transcriptase PCR (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 using haemagglutination inhibition test.
Equine influenza virus infection was confirmed using real-time RT-PCR and serological testing. The phylogenetic analysis of the HA and NA genes revealed that 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 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.
The study does not include antigenic characterisation and full genome sequencing of Argentinian strains, that could provide additional information.
The occurrence of this multifocal equine influenza outbreak in regularly vaccinated horses is a field evidence of vaccine breakdown, reinforcing the necessity of keeping vaccine strains updated according to OIE recommendations. It also underlines the importance of the implementation of appropriate quarantine measures and restriction of horse movement in the face of disease.
马流感是世界范围内马呼吸系统疾病的重要病因。马流感病毒（EIV）通过病毒蛋白中氨基酸替换的积累而发生抗原漂移，这可能导致疫苗失效。
描述 2018 年 3 月至 7 月期间在阿根廷发生的多病灶暴发期间检测到的 EIV 的流行病学发现和分子特征，并证明疫苗失效。
观察性、描述性研究。
使用实时逆转录聚合酶链反应（RT-PCR）从鼻拭子中检测病毒。从 EIV 阳性鼻拭子中获得血凝素（HA）和神经氨酸酶（NA）基因的核苷酸和推导的氨基酸序列，并进行系统进化分析。将氨基酸序列与当前世界动物卫生组织（OIE）推荐的佛罗里达 1 分支疫苗株以及阿根廷使用的疫苗株成分进行比较。使用血凝抑制试验检测血清样本。
使用实时 RT-PCR 和血清学检测确认了马流感病毒感染。HA 和 NA 基因的系统进化分析表明，暴发期间鉴定的所有 EIV 均属于 H3N8 亚型，佛罗里达 1 分支。与阿根廷常用疫苗中包含的菌株相比，循环病毒中观察到多个氨基酸变化，其中一些位于抗原位点。76%受影响的马已接种该疫苗，表明发生了疫苗失效。
该研究不包括抗原特征和阿根廷毒株的全基因组测序，这可能提供更多信息。
在定期接种疫苗的马中发生这种多病灶马流感暴发是疫苗失效的现场证据，这强调了根据 OIE 建议更新疫苗株的必要性。它还强调了在疾病面前实施适当的检疫措施和限制马匹运动的重要性。
