Isolation of influenza A viruses from migratory waterfowl in San-in District, western Japan in the winter of 1983-1984

Certain species of winter migratory waterfowl in San-in District, western Japan, were surveyed for influenza virus from November 1983 to March 1984. Faeces of the waterfowl were collected regularly at five stations. Eleven influenza A viruses including H5N3 and H10N4 subtypes were isolated from 450 faecal samples from whistling swans, 28 viruses including H2N2 and H10N4 subtypes were isolated from 362 faecal samples from pintails; and subtype H13N6 was isolated from 240 faecal samples of black-tailed gulls.     

上海地区活禽批发市场H9亚型禽流感病毒调查

为弄清上海地区活禽批发市场中H9禽流感病毒（Avian influenza virus,AIV）的流行情况及鸡群的免疫情况,2009年对上海三大活禽批发市场进行了采样监测。采用HI试验检测H9 AIV抗体、荧光RT-PCR试验和鸡胚接种分离鉴定病毒。共采集110批次1 646份血样和喉头泄殖腔棉拭样品,平均抗体合格率为60.27%,分离到H9病毒134株,其中4-6月和9-11月为全年中病毒分离的2个高峰期（样品带毒率均超过了10.00%）,明显比其它月份要高（其他月份均低于5.00%）,样品带毒率平均为8.14%。不同市场、不同地区采集的样品其抗体合格率和样品的带毒率也存在一定的差异。在30批分离到病毒的样品中,13批次已免疫H9N2油乳剂灭活苗且抗体合格率均大于70.00%的样品中分离到45株病毒（45/195）,其中6批次抗体合格率达到100%的样品中也分离到了病毒（8/90）,但带毒率明显比未经疫苗免疫的样品（79/255）低。调查结果表明养殖户对肉鸡群H9N2油乳剂灭活苗免疫重视程度不够,鸡群中带毒现象较普遍。疫苗免疫后能产生较高的免疫抗体,且抗体能减轻临床症状,降低带毒率,但不能完全阻止病毒复制,存在高抗体下带毒现象。     

Influenza surveillance in birds in Italian wetlands (1992-1998): is there a host restricted circulation of influenza viruses in sympatric ducks and coots?

We report the results of a 6-year serological and virological monitoring performed in ducks and coots in Italy, in order to assess the degree of influenza A virus circulation in these birds during wintering. A total of 1039 sera collected from 1992 to 1998 was screened by a double antibody sandwich blocking ELISA (NP-ELISA): seroprevalence of antibodies to influenza A viruses was significantly higher in ducks compared to coots (52.2% vs. 7.1%, respectively). The hemagglutination-inhibition (HI) assay, performed on NP-ELISA positive sera, showed that 16.9% of these duck sera and 33.3% of these coot sera had antibodies to at least one influenza virus HA subtype: ducks showed HI antibodies against most of the HA subtypes, except for the H3, H4, H7, and H12; coots were seropositive to the H3 and H10 subtypes, only. From 1993 to 1998, 22 virus strains were obtained from 802 cloacal swabs, with an overall virus isolation frequency of 2.7%. Viruses belonging to the H1N1 subtype were by far the most commonly circulating strains (18/22) and were isolated mainly from ducks (17/18). The remaining viruses were representative of the H10N8, H5N2 and H3N8 subtypes. Our data indicate some differences between influenza A virus circulation in sympatric ducks and coots and a significant antigenic diversity between some reference strains and viruses recently isolated in Italy.     

H9N2亚型禽流感病毒血凝素和神经氨酸酶基因的遗传分析

H9N2亚型禽流感病毒自1994年在中国首次发现以来,一直在家禽中流行,其导致的产蛋下降和发病死亡给养禽业发展带来严重危害。以前的研究发现中国的H9N2亚型禽流感病毒在进化过程中形成多个基因型,其表面抗原蛋白血凝素基因(HA)可被划分为以A/chicken/Beijing/1/94、A/quail/Hong Kong/G1/97(G1)和A/chicken/Heilongjiang/35/01等为代表的3个亚群,神经氨酸酶基因(NA)可被划分为以A/chicken/Beijing/1/94、A/quail/Hong Kong/G1/97(G1)和A/chicken/Hong Kong/G9/97(G9)等为代表的3个亚群。其中类G1病毒的HA基因只在香港分离株中出现。本研究对我国2003年～2004年从禽类中分离的H9N2亚型禽流感病毒血凝素(HA)和神经氨酸酶(NA)基因进行测定和遗传演化分析,结果表明其中11株病毒的HA基因属于CK/BJ/1/94群系,NA基因属于CK/BJ/1/94或DK/HK/G9/97群系,并首次发现两株病毒含有类G1病毒HA和NA基因,而且这些类G1病毒具有不同的抗原性以及人流感病毒的受体结合位点。本研究结果提示应对H9N2病毒的防治及其公共卫生意义予以高度重视。     

Avian influenza A viruses in birds --an ecological, ornithological and virological view

Avian influenza A viruses (AIV) are the causative agents of the presently most important poultry disease. Ten countries in Asia and several other countries in Eastern Europe suffer high losses from the lethal effects of these viruses of the H5N1 subtype. AIV of other subtypes cause in additional countries severe losses. The threat to health and well-being of the avifauna, domestic poultry and possibly mammals including humans are worldwide of major concern. The European Union reacted with a complete import ban on untreated meat, eggs, poultry products as well as free-living and pet birds. Extensive surveillance of free-living birds and domestic poultry that is maintained in free-range and close to open waters were initiated in an attempt to gather information on the current status of infection with these viruses and to target appropriate countermeasures for the protection of domestic poultry (in-house keeping) and to safeguard food production for humans. Since the monitoring of free-living birds is labour-intensive, costly, and time-consuming, only birds should be included in the monitoring programme that harboured in the past most if not all influenza A viruses. The birds of the order Anatiformes, family Anatidae, subfamilies Anserinae and Anatinae, provided 65.9 % of all avian AIV isolates. The cosmopolitan Common Mallard (Anas platyrhynchos) is the dominant species with the highest rate of isolations among all bird species. Second in frequency is the North-American Blue-winged Teal (Spatula discors). Consequently, free-living anatiform birds of the genera Anas and Spatula should comprise the main focus for the collection of cloacal and pharyngeal swabs. With the likely exception of the most recent H5N1 viruses, signs of disease were not recorded in AIV infected anatiform birds. AIV isolations were definitely less frequently obtained from birds of the orders Phasianiformes (including domestic chickens and turkeys), Charadriiformes (plovers and lapwings), Lariformes (gulls), Columbiformes (pigeons) and Psittaciformes (psittacines) and need less attention in sampling efforts. This review presents also data on taxonomy and most suitable means for isolation and typing of haemagglutinating viruses. The different frequencies of the detection of 16 haemagglutinin (HA) subtypes and 9 subtypes of neuraminidase (NA) surface antigens are composed on the basis of extensive literature retrievals. Both antigens occure in isolates at different frequencies. Only 103 of all 144 possible HA x NA combinations were described so far. The AIV that contain the HA subtypes H3, H4, H6 are most frequently isolated whereas the AIV of the subtypes H5 and H7 were less frequently encountered. All other HAs are rather rare. AIV that possess the NA of the subtypes N2, N1, N8 and N3 are frequent and all other NAs are rarely detected.     

Surveillance and identification of influenza A viruses in wild aquatic birds in the Crimea, Ukraine (2006-2008)

The ecology of avian influenza (AI) viruses in wild aquatic birds of Asia is poorly understood, especially for the H5N1 high pathogenicity AI (HPAI) viruses. From March 2006 through November 2008, 20 AI viruses were isolated in the Crimea region of Ukraine with an overall frequency of virus recovery of 3.3%. All the viruses were isolated from three species of dabbling ducks: mallard (Anas platyrhynchos), wigeon (Anas penelope), and garganey (Anas querquedula), making the frequency of virus recovery for dabbling ducks 6.3%. The viruses were predominantly isolated during the fall sampling period. All viruses were genetically and antigenically characterized. No H5N1 HPAI viruses were isolated, but other HA and NA subtypes were identified including H3N1 (2), H3N6 (3), H3N8 (4), H4N6 (6), H5N2 (3), H7N8 (1), and H10N6 (1) subtypes. All isolates were of low pathogenicity, as determined by the intravenous pathogenicity index of 0.00. For H5N2 and H7N8 isolates, the HA gene was sequenced and the phylogenetic analysis revealed possible ecologic connections of the Crimea region with AI viruses from Siberia and Europe. No influenza A isolates were recovered from other Anseriformes (diving ducks [two species of pochards] and graylag geese), Columbiformes (collared doves), Gruiformes (coot), and Galliformes (gray partridges).     

Virological Surveillance and Preliminary Antigenic Characterization of Influenza Viruses in Pigs in Five European Countries from 2006 to 2008

This study presents the results of the virological surveillance for swine influenza viruses (SIVs) in Belgium, UK, Italy, France and Spain from 2006 to 2008. Our major aims were to clarify the occurrence of the three SIV subtypes – H1N1, H3N2 and H1N2 – at regional levels, to identify novel reassortant viruses and to antigenically compare SIVs with human H1N1 and H3N2 influenza viruses. Lung tissue and/or nasal swabs from outbreaks of acute respiratory disease in pigs were investigated by virus isolation. The hemagglutinin (HA) and neuraminidase (NA) subtypes were determined using standard methods. Of the total 169 viruses, 81 were classified as ‘avian‐like’ H1N1, 36 as human‐like H3N2 and 47 as human‐like H1N2. Only five novel reassortant viruses were identified: two H1N1 viruses had a human‐like HA and three H1N2 viruses an avian‐like HA. All three SIV subtypes were detected in Belgium, Italy and Spain, while only H1N1 and H1N2 viruses were found in UK and Northwestern France. Cross‐hemagglutination inhibition (HI) tests with hyperimmune sera against selected older and recent human influenza viruses showed a strong antigenic relationship between human H1N1 and H3N2 viruses from the 1980s and H1N2 and H3N2 human‐like SIVs, confirming their common origin. However, antisera against human viruses isolated during the last decade did not react with currently circulating H1 or H3 SIVs, suggesting that especially young people may be, to some degree, susceptible to SIV infections.     

2009—2010年华东地区家禽低致病性禽流感病毒的流行病学调查与分析

为了解华东地区家禽中低致病性禽流感病毒（low pathogenic avian influenza viruses,LPAIVs）的分布规律,从2009年10月到2010年9月在华东地区某活禽市场采集鸡、鸭、鹅等家禽的泄殖腔拭子共1 650份,经鸡胚接种和HA、HI试验鉴定,结果从58份样品中分离到了LPAIVs,总分离率为3.51%。所分离到的6种HA亚型及各HA亚型分离率从高到底依次为：H6、H3、H1、H4、H9、H11。从这些样品中鉴定出7种NA亚型,包括N1、N2、N3、N4、N5、N6、N8,二者之间有11种组合。家鸭样品中LPAIVs的分离率为7.28%,显著高于鸡源样品的分离率1.00%和鹅源样品的分离率1.02%。LPAIVs的季节性分布较为明显,3～6月份和10～12月份的分离率较高,而冬季最冷的1月份和夏季最热的7月份则没有分离到。2种或2种以上不同HA亚型混合感染的样品有6份,全部为水禽源样品,占总阳性样品数的10.34%。这些数据表明活禽市场可以作为AIV的一个重要储存库,而家养水禽可作为AIV的一个重要储存宿主,应该继续加强对活禽市场,尤其是家养水禽中AIV的监测。     

猪流感病毒H1N1、H1N2和H3N2亚型多重RT-PCR诊断方法的建立

对我国分离到的猪流感病毒和GenBank数据库中已有的猪流感病毒H1N1、H1N2和H3N2亚型毒株的HA、NA基因核苷酸序列进行分析,分别选出各个病毒亚型HA和NA基因中高度保守且特异的核苷酸区域,设计扩增猪流感病毒H1和H3、N1和N2亚型的2套多重PCR特异性引物,建立了猪流感H1N1、H1N2和H3N2亚型病毒多重RT-PCR诊断方法。采用该方法对H1N1、H1N2、H3N2亚型猪流感病毒标准参考株进行RT-PCR检测,结果均呈阳性,对扩增得到的片段进行序列测定和BLAST比较,表明为目的基因片段。其它几种常见猪病病毒和其它亚型猪流感病毒的RT-PCR扩增结果都呈阴性。对107EID50/0.1mL病毒进行稀释,提取RNA进行敏感性试验,RT-PCR最少可检测到102EID50的病毒量核酸。对40份阳性临床样品的检测结果是H1N1、H1N2和H3N2亚型分别为16份、1份和20份,其它3份样品同时含有H1N1和H3N2亚型猪流感病毒,和鸡胚分离病毒结果100%一致。试验证明建立的猪流感病毒H1N1、H1N2和H3N2亚型多重RT-PCR诊断方法是一种特异敏感的诊断方法,可用于临床样品的早期快速诊断和分型。     

Molecular characterization of low pathogenic avian influenza viruses, isolated from food products imported into Singapore

We have completed the genetic characterization of all eight gene segments for four low pathogenic avian influenza (LPAI) viruses. The objective of this study was to detect the presence of novel signatures that may serve as early warning indicators of the conversion of LPAI viruses to high pathogenic avian influenza (HPAI) viruses. This study included three H5N2 and one H5N3 viruses that were isolated from live poultry imported into Singapore as part of the national avian influenza virus (AIV) surveillance program. Based on the molecular criterion of the World Organisation for Animal Health (OIE), sequence analysis with the translated amino acid (aa) sequence of the hemagglutinin (HA) gene revealed the absence of multibasic aa at the HA cleavage site, identifying all four virus isolates as LPAI. Detailed phylogenetic tree analyses using the HA and neuraminidase (NA) genes clustered these isolates in the Eurasian H5 lineage, but away from the HPAI H5 subtypes. This analysis further revealed that the internal genes clustered to different avian and swine subtypes, suggesting that the four isolates may possibly share their ancestry with these different influenza subtypes. Our results suggest that the four LPAI isolates in this study contained mainly avian signatures, and the phylogenetic tree for the internal genes further suggests the potential for reassortment with other different circulating avian subtypes. This is the first comprehensive report on the genetic characterization of LPAI H5N2/3 viruses isolated in South-East Asia.     

鸭源H5N1亚型高致病性禽流感病毒的分离鉴定及其HA和NA基因的生物信息分析

分离到1株 H5N1亚型高致病性禽流感病毒, 经序列测定发现HA蛋白裂解位点上插入多个连续的碱性氨基酸（PQREIRRKKR*G）,从分子上证实是一株高致病性禽流感病毒。核酸序列比较分析结果表明,分离的流感病毒HA基因与A/duck/VietNam/Ncvd1/2002(H5N1)同源率最高,达到98.8%;NA基因与A/duck/VietNam/Ncvd1/2002(H5N1) 和A/chicken/Jiangsu/cz1/2002(H5N1)同源率最高,达到98.7%。氨基酸水平上,HA与A/duck/Viet Nam/Ncvd1/2002(H5N1)同源率最高,可达99.3%;NA与A/chicken/Jiangsu/cz1/2002(H5N1)同源率最高,达98.7%。HA与NA基因的潜在糖基化位点与作者所选参比毒株一致。通过遗传进化树分析结果表明,A/duck/VietNam/Ncvd1/2002(H5N1)可能是该毒株的来源株。     

Host range of A/Chicken/Pennsylvania/83 (H5N2) influenza virus

The highly pathogenic A/Chicken/Penn./1370/83 (H5N2) avian influenza virus, which caused 80% mortality in chickens in Pennsylvania, produced only mild transient illness in experimentally infected pheasants, little or no clinical signs in ring-billed gulls and pigs, and no clinical signs in pekin ducks. Virus could be recovered from only the upper respiratory tract of gulls and pigs for 1-2 days. Infection in ducks resulted in intestinal replication of virus in only 1 out of 12 ducks. By contrast, pheasants shed virus in feces (10(4.7) EID50) for at least 15 days. These studies reinforce wildlife surveillance findings indicating that gulls and ducks are unlikely to have transmitted virus between chicken farms during the 1983 outbreak. Although experimental data suggest that wild gallinaceous birds such as pheasants are potentially capable of virus transmission, there has been no evidence of this from wildlife surveillance in Pennsylvania. Experimental infection of chickens with H5N2 virus isolated from wild ducks one year before the Pennsylvania outbreak or a gull virus (H5N1) isolated in the quarantine area in 1983 resulted in asymptomatic infections and virus replication occurring only in the upper respiratory tract. These studies suggest that if the first H5N2 virus infecting chickens in Pennsylvania originated from waterbirds, changes in host specificity and pathogenicity for chickens and other gallinaceous birds probably occurred during emergence of the Chicken/Penn./83 virus. It is recommended that attention be given in the future to the isolation of domestic poultry from contact with wild aquatic birds.     

禽流感病毒N4亚型神经氨酸酶基因的克隆和序列分析

应用无特定病原体 (SPF)鸡胚增殖禽流感病毒 A/ Turkey/ Ontario/ 6 118/ 6 8(H8N4 )毒株 ,Tri Zol L S Reagent提取病毒 RNA,RT- PCR扩增神经氨酸酶 (NA)基因全片段 ,克隆到 p MD18- T载体上 ,并进行了鉴定和序列测定。所获得的 NA基因片段长 14 4 1bp,编码 4 90个氨基酸残基。根据推导的氨基酸序列进行预测 ,有 9个潜在的糖基化位点和2 0个半胱氨酸残基     

福建省H9N2亚型禽流感病毒HA和NA基因的进化分析

为进一步了解福建省H9N2亚型禽流感病毒的基因遗传进化关系,本研究将福建省2011年分离的毒株FZ-04、FZ-11与GenBank上登录的2000～2011年福建省分离的H9N2毒株及国内外典型代表株进行HA、NA基因的序列比对和遗传进化分析。结果表明,分离株FZ-04和FZ-11的HA基因与CK/FJ/G9/09株核苷酸同源性最高,属于国内常见的CK/BJ/1/94亚系。HA裂解位点处的氨基酸序列为-PSRSSR/GL-,符合低致病性禽流感病毒的分子特征。NA基因在遗传进化关系上呈现独立的分支,与CK/FJ/10954/05毒株核苷酸序列同源性最高,属于CK/HK/G9/97亚系,且NA基因推导的469个氨基酸序列中没有缺失。同时,从HA和NA基因的遗传进化树上可知,2000～2011年福建省H9N2禽流感病毒进化相对比较稳定,可能有一个共同的起源。     

Prevalence and subtypes of Influenza A Viruses in Wild Waterfowl in Norway 2006-2007

The prevalence of influenza A virus infection, and the distribution of different subtypes of the virus, were studied in 1529 ducks and 1213 gulls shot during ordinary hunting from August to December in two consecutive years, 2006 and 2007, in Norway. The study was based on molecular screening of cloacal and tracheal swabs, using a pan-influenza A RT-PCR. Samples found to be positive for influenza A virus were screened for the H5 subtype, using a H5 specific RT-PCR, and, if negative, further subtyped by a RT-PCR for the 3''-part of the hemagglutinin (HA) gene, encompassing almost the entire HA2, and the full-length of the neuraminidase (NA) gene, followed by sequencing and characterization. The highest prevalence (12.8%) of infection was found in dabbling ducks (Eurasian Wigeon, Common Teal and Mallard). Diving ducks (Common Goldeneye, Common Merganser, Red-breasted Merganser, Common Scoter, Common Eider and Tufted Duck) showed a lower prevalence (4.1%). In gulls (Common Gull, Herring Gull, Black-headed Gull, Lesser Black-headed Gull, Great Black-backed Gull and Kittiwake) the prevalence of influenza A virus was 6.1%. The infection prevalence peaked during October for ducks, and October/November for gulls. From the 16 hemagglutinin subtypes known to infect wild birds, 13 were detected in this study. Low pathogenic H5 was found in 17 dabbling ducks and one gull.     

猪流感病毒H1、H3、N1、N2亚型分型 RT-PCR方法的建立

根据GenBank中H1N1和H3N2亚型猪流感病毒(SIV)血凝素(hemagglutinin,HA)、神经氨酸酶(neuraminidase,NA)和M基因保守序列,分别设计合成了5对特异性引物,利用RT-PCR技术对SIV的型和亚型进行鉴定。结果表明,该方法的型RT-PCR可以检测出10⁴ EID₅₀病毒量所提取的RNA;H1、H3、N1和N2的亚型RT-PCR均可以检测出10⁴ EID₅₀病毒量所提取的RNA。除每对特异性引物所对应的亚型外,对其他亚型及猪繁殖与呼吸综合征病毒(PRRSV)和猪瘟病毒(CSFV)的检测均为阴性,应用该方法对临床样品进行检测,其结果与病毒分离结果符合率为100%。结果表明,该方法特异性好、敏感性高,有望成为SIV的一种特异、敏感、快速的分型检测方法,为猪流感分子流行病学的调查奠定了良好的基础。     

上海地区野鸟中禽流感的流行病学监测

为了评估野鸟在禽流感流行病学中的作用,于2004年4月-2005年6月间对上海地区捕捉到的63个品种的1 010只野鸟进行了血样和喉肛棉拭样品的采集.采用病毒分离试验和荧光RT-PCR试验对喉肛棉拭样品进行了病原学检测,结果均为阴性;采用HA和HI试验进行了禽流感血清抗体的检测,结果在15种野鸟的587份血样中检出了44份AIV阳性抗体,其中H1阳性数3份,阳性率为0.51%;H3阳性数4份,阳性率为0.68%;H5阳性数11份,阳性率为1.87%;H9阳性数26份,阳性率为4.43%.     

Susceptibility of laughing gulls (Larus atricilla) to H5N1 and H5N3 highly pathogenic avian influenza viruses

This investigation detailed the clinical disease, gross and histologic lesions, and distribution of viral antigen in juvenile laughing gulls (Larus atricilla) intranasally inoculated with either the A/tern/South Africa/61 (H5N3) (tern/SA) influenza virus or the A/chicken/Hong Kong/220/97 (H5N1) (chicken/HK) influenza virus, which are both highly pathogenic for chickens. Neither morbidity nor mortality was observed in gulls inoculated with either virus within the 14-day investigative period. Gross lesions resultant from infection with either virus were only mild, with the tern/SA virus causing decreased lucency of the air sacs (2/6), splenomegaly (2/6), and pancreatic mottling (1/6) and the chicken/HK virus causing only decreased lucency of the air sacs (2/8) and conjunctival edema (2/8). Histologic lesions in the tern/SA-inoculated gulls included a mild to moderate heterophilic to lymphoplasmacytic airsacculitis (6/6), mild to moderate interstitial pneumonia (3/6), and moderate necrotizing pancreatitis and hepatitis at 14 days postinoculation (DPI) (2/6). Immunohistochemical demonstration of viral antigen occurred only in association with lesions in the liver and pancreas. In contrast, viral antigen was not demonstrated in any tissues from the chicken/HK-inoculated gulls, and inflammatory lesions were confined to the air sac (3/8) and lungs (3/8). Both viruses were isolated at low titers (<10(1.68) mean embryo lethal dose) from oropharyngeal and cloacal swabs up to 7 days postinoculation (DPI), from the lung and kidney of one of two tern/SA-inoculated gulls at 14 DPI, and from the lung of one of two chicken/HK-inoculated gulls at 7 DPI. Antibodies to influenza viruses as determined with the agar gel precipitin test at 14 DPI were detected only in the two tern/SA-inoculated gulls and not in the two chicken/HK-inoculated gulls.     

一株野鸟源重组禽流感(H6N1)病毒基因组分子特征分析

2017年在江苏省野生豆雁粪便中分离得到1株H6N1亚型禽流感病毒A/Anser fabalis/Jiangsu/J746/2017(H6N1)(J746)。本研究对J746进行了全基因组测序,并对其进行了遗传进化分析。遗传进化分析结果表明:与HA和NA基因同源性最高的毒株为A/wild waterfowl/Korea/F14-5/2016(H6N1),同源性为99.4%。HA基因与流行于韩国、日本和孟加拉的N1、N2、N8亚型毒株处于同一分支,NA基因与韩国野生水禽的H6、H7亚型毒株处于同一分支,PB2基因与中亚及东亚地区低致性病毒株处于同一分支,PB1基因和NP基因与流行在东南亚的低致病性毒株处于同一分支,PA基因和M基因均处于欧亚分支,但PA形成了独立的小分支,NS基因与分离于中国中南部和日本的毒株聚集在一起。氨基酸位点分析表明,神经氨酸(NA)蛋白存在H274Y突变,该突变可增强病毒对神经氨酸酶抑制剂药物的耐药性;同时在PB2蛋白中发现与增强对小鼠致病性有关的L89V突变,在NS1蛋白中发现与增强对小鼠致病性、提高复制能力和改变宿主嗜性有关的P42S、L103F、I106M、N205S突变。综上所述,J746毒株基因组构成来源复杂,是由多个国家和地区形成的一株多元重组病毒。