van Maanen C, van Essen G J, Minke J, Daly J M, Yates P J
Animal Health Service, P.O. Box 9, 7400 AA, Deventer, The Netherlands.
Vet Microbiol. 2003 Jun 10;93(4):291-306. doi: 10.1016/s0378-1135(03)00029-4.
An outbreak of equine influenza H3N8 in a riding school is described retrospectively with emphasis on diagnosis and putative vaccine failure. In March 1995 an outbreak of equine influenza occurred among 11 horses in a riding school, where most horses had received basic primary immunizations and several booster vaccinations against influenza. Six of the 11 diseased horses had received their last booster vaccination within 5 months of the outbreak. Nevertheless, the influenza infection spread rapidly and clinical manifestations were prominent with frequent, harsh, dry coughing often accompanied by high fever. Nasal swabs were taken from 11 diseased horses. Influenza A virus of the equine H3N8 (equi-2) subtype was isolated from five nasal swab extracts. Stored nasal swab extracts were also retrospectively investigated in two different enzyme immunoassays designed to detect the type-specific conserved nucleoprotein of influenza A viruses, and in a single-tube reverse transcription-PCR (RT-PCR) using a set of primers based on highly conserved regions of the matrix gene of influenza A viruses. Five nasal swab extracts were found positive in a DAS-ELISA and seven in the Directigen((R)) Flu A (DFA) assay, respectively. Two nasal swab extracts from which virus was isolated did not give a positive result in the DAS-ELISA, and one of these also did not give a positive result in the DFA assay. Nine nasal swab extracts were found positive by RT-PCR. Moreover, all virus isolation and/or ELISA positive nasal swab extracts were confirmed by RT-PCR. Three nasal swab extracts were negative by virus isolation, PCR and ELISA. A significant rise in HI titre against influenza A/eq/Miami/63 (H3N8) virus was detected in seven of the nine paired sera available. In acute phase serum samples from 10 horses, SRH antibody levels varied widely. However, some horses with high, or at least putatively clinically protective SRH antibody levels, showed clinical signs and infection was confirmed. Antigenic analysis of two isolates showed that A/eq/Holland/1/95 (H3N8) and A/eq/Holland/2/95 (H3N8) cluster with the UK isolate Osgodsby/92, the Swedish isolate Borlänge/91 and some other European isolates, with H/2/95 identical in reactivity to Borlänge/91 and H/1/95 more similar in reactivity to Osgodsby/92 than H/2/95. Nucleotide and deduced amino-acid sequences showed large differences of both isolates as compared with Miami/63, Fontainebleau/79 and Kentucky/81, the influenza A H3N8 subtype strains incorporated in the vaccines used in this riding school. The role of antigenic drift in vaccine breakdown is discussed in the light of evidence for vaccine breakdown in the UK in 1989, Sweden in 1991 and in the USA since 1991.
本文回顾性描述了一所马术学校发生的H3N8型马流感疫情，重点在于诊断和假定的疫苗失效情况。1995年3月，一所马术学校的11匹马中爆发了马流感，该校大多数马匹都接受过针对流感的基础初次免疫和几次加强免疫接种。11匹患病马匹中有6匹在疫情爆发前5个月内接受了最后一次加强免疫接种。然而，流感感染迅速传播，临床表现明显，频繁出现剧烈、干咳，常伴有高热。从11匹患病马匹采集了鼻拭子。从5份鼻拭子提取物中分离出了马H3N8（equi - 2）亚型的甲型流感病毒。还对储存的鼻拭子提取物进行了回顾性研究，采用两种不同的酶免疫测定法检测甲型流感病毒的型特异性保守核蛋白，以及使用一组基于甲型流感病毒基质基因高度保守区域的引物进行单管逆转录 - 聚合酶链反应（RT - PCR）。在双抗体夹心酶联免疫吸附测定（DAS - ELISA）中，5份鼻拭子提取物呈阳性，在直接免疫荧光法（Directigen((R)) Flu A，DFA）检测中，7份呈阳性。从其中分离出病毒的两份鼻拭子提取物在DAS - ELISA中未得出阳性结果，其中一份在DFA检测中也未得出阳性结果。9份鼻拭子提取物经RT - PCR检测呈阳性。此外，所有病毒分离和/或ELISA阳性的鼻拭子提取物均经RT - PCR确认。3份鼻拭子提取物经病毒分离、PCR和ELISA检测均为阴性。在可得的9对血清样本中，7份检测到针对甲型/马/迈阿密/63（H3N8）病毒的血凝抑制（HI）效价显著升高。在10匹马的急性期血清样本中，血清反应素（SRH）抗体水平差异很大。然而，一些SRH抗体水平高或至少假定具有临床保护作用的马匹出现了临床症状，且感染得到了确认。对两株分离株的抗原分析表明，A/马/荷兰/1/95（H3N8）和A/马/荷兰/2/95（H3N8）与英国分离株奥斯戈德比/92、瑞典分离株博伦厄/91以及其他一些欧洲分离株聚类，H/2/95与博伦厄/91的反应性相同，H/1/95与奥斯戈德比/92的反应性比H/2/95更相似。与该校使用的疫苗中所含的甲型流感H3N8亚型毒株迈阿密/63、枫丹白露/79和肯塔基/81相比，两株分离株的核苷酸和推导氨基酸序列显示出很大差异。结合1989年英国、199?1年瑞典以及自1991年以来美国出现疫苗失效的证据，讨论了抗原漂移在疫苗失效中的作用。 （注：原文中“199?1年”疑似有误，可能是1991年，译文按1991年翻译）
