云南蓝舌病病毒1型毒株M6基因序列分析

为了解云南蓝舌病病毒(Bluetongue virus,BTV) 1型M6基因流行株的遗传变异及其与国内外流行病毒的遗传进化关系,试验从细胞培养物中分别提取4株云南分离株BTV-1 (Y863、SZ120169、6-12和7-12) RNA,用M6基因特异引物进行RT-PCR扩增和测序,采用生物信息学软件对获得的M6基因编码区序列进行核苷酸、氨基酸同源性比对及遗传进化分析.结果表明,分别获得4株云南分离株BTV-1 M6基因1 763 bp序列;4株云南分离株BTV-1核苷酸同源性在95.2%~99.9%之间,氨基酸同源性在97.6%~99.8%之间,1979年师宗分离的Y863病毒毒株与2012年师宗(SZ120169)、2013年江城(6-12、7-12)分离的3株病毒毒株核苷酸同源性分别为95.5%、95.2%和95.2%,氨基酸同源性分别为97.6%、98.4%和98.2%,而近两年(2012、2013)分离病毒核苷酸和氨基酸同源性较高,分别在96.9%~99.9%和99.1%~99.8%之间;遗传进化分析发现,4株云南分离株BTV-1为Eastern基因群病毒,它们之间核苷酸和氨基酸同源性分别为95.2%~99.9%和97.6%~99.8%;进一步分析发现4株云南分离株BTV-1与希腊及澳大利亚 BTV-1型毒株亲缘关系较近,核苷酸和氨基酸同源性分别为90.4%~95.6%和95.1%~99.1%,而与地中海国家(意大利、法国、阿尔及利亚、摩洛哥和突尼斯)和南非毒株关系较远,核苷酸和氨基酸同源性分别在83.8%和95.7%以下.4株云南分离株BTV-1属于Eastern基因群病毒,云南分离株BTV-1 M6基因在自然进化中发生遗传变异缓慢,该基因可以用来进行BTV-1基因群分布及毒株的地理区域来源相关的研究.     

云南江城蓝舌病病毒16型毒株分离鉴定及其L2基因序列分析

为了解近年来云南江城县蓝舌病病毒16型(Bluetongue virus type 16,BTV-16)毒株的流行情况及其L2基因与国外流行株的遗传进化关系,本研究将江城县送检的300份牛肝素钠抗凝血提取红细胞后静脉接种10日龄鸡胚,将收集的鸡胚肝脏捣碎离心,上清液接种于C6/36和BHK21细胞传代。针对出现细胞病变的样品,应用群特异性VP7片段引物进行RT-PCR检测,应用BTV-16 L2基因特异性引物对检测出的BTV核酸阳性样品进行RT-PCR扩增和测序,采用DNAStar和Mega 6.0软件对获得的L2基因编码区序列进行核苷酸、氨基酸同源性比对及遗传进化分析,同时利用BTV-16标准阳性血清对分离到的病毒进行中和试验鉴定。结果显示,江城县发现30个可致细胞病变的样品,其中17个样品经RT-PCR初步确认为BTV;经L2基因序列分析和中和试验鉴定,确定其中6株为BTV-16型毒株;核苷酸、氨基酸同源性比对分析结果显示,6个毒株核苷酸和氨基酸同源性分别在93.4%～98.0%和94.2%～99.1%之间;遗传进化分析发现,其中5株与2001—2008年日本及1982—2011年印度分离的BTV-16毒株亲缘关系较近;1株与1985—1990年日本分离的BTV-16毒株亲缘关系较近。本研究发现,云南江城县BTV-16毒株呈现新旧毒株交叉持续流行态势,但在自然进化中遗传变异不大,有一定的稳定性,本研究在分子水平阐明了云南江城县地方流行BTV-16 L2基因间的遗传和差异,为进一步开展BTV分子流行病学及检测研究提供科学依据。     

云南江城蓝舌病病毒16型毒株分离鉴定及其L2基因序列分析

为了解近年来云南江城县蓝舌病病毒16型（Bluetongue virus type 16,BTV-16）毒株的流行情况及其L2基因与国外流行株的遗传进化关系,本研究将江城县送检的300份牛肝素钠抗凝血提取红细胞后静脉接种10日龄鸡胚,将收集的鸡胚肝脏捣碎离心,上清液接种于C6/36和BHK21细胞传代。针对出现细胞病变的样品,应用群特异性VP7片段引物进行RT-PCR检测,应用BTV-16 L2基因特异性引物对检测出的BTV核酸阳性样品进行RT-PCR扩增和测序,采用DNAStar和Mega 6.0软件对获得的L2基因编码区序列进行核苷酸、氨基酸同源性比对及遗传进化分析,同时利用BTV-16标准阳性血清对分离到的病毒进行中和试验鉴定。结果显示,江城县发现30个可致细胞病变的样品,其中17个样品经RT-PCR初步确认为BTV;经L2基因序列分析和中和试验鉴定,确定其中6株为BTV-16型毒株;核苷酸、氨基酸同源性比对分析结果显示,6个毒株核苷酸和氨基酸同源性分别在93.4%~98.0%和94.2%~99.1%之间;遗传进化分析发现,其中5株与2001-2008年日本及1982-2011年印度分离的BTV-16毒株亲缘关系较近;1株与1985-1990年日本分离的BTV-16毒株亲缘关系较近。本研究发现,云南江城县BTV-16毒株呈现新旧毒株交叉持续流行态势,但在自然进化中遗传变异不大,有一定的稳定性,本研究在分子水平阐明了云南江城县地方流行BTV-16 L2基因间的遗传和差异,为进一步开展BTV分子流行病学及检测研究提供科学依据。     

12个新城疫病毒分离株的F基因和HN基因序列分析

自1997年-2016年从广东佛山、肇庆、云浮等地疑似新城疫的家禽病料分离鉴定获得12株新城疫病毒,采用RT-PCR方法对所有分离株的F基因和HN基因进行扩增,产物经克隆并测序后与GenBank数据库中的参考毒株做遗传进化分析。12个分离株的F基因遗传进化分析结果显示,9株属于基因Ⅶ型,2株属于基因Ⅸ型,1株属于基因Ⅵ型。F基因同源性分析结果显示,12个毒株与目前疫苗株La Sota、B1、Mukteswar和Clone30的同源性在81.6%~91.5%之间,12个毒株间同源性的差异较大,9个Ⅶ型分离株之间的同源性在84.8%~99%之间;HN基因同源性分析结果显示,12个毒株与目前疫苗株La Sota、B1、Mukteswar和Clone30的同源性在80.9%~91.9%之间,12个毒株间同源性的差异较大,9个Ⅶ型分离株之间的同源性在84%~98.5%之间。氨基酸序列分析表明,12个分离株与NDV强毒株的氨基酸特征相符,有10个分离株的HN基因第514氨基酸残基出现Ⅰ→Ⅴ的变异,有9个分离株的F基因和HN基因的中和抗原位点出现变异。试验提示,当前广东部分地区的分离株与传统疫苗株之间存在抗原性差异,故应加强广东地区新城疫病毒的分子遗传监控。     

10株广西野鸟源新城疫病毒HN基因的遗传进化分析

对分离自广西4种鸟类的10株新城疫病毒(NDV)分离株,进行HN基因的RT-PCR扩增、序列测定和分析,旨在探讨广西野鸟源NDV HN基因的分子进化特征,为科学防控新城疫提供依据。结果显示,10株广西野鸟源NDV分离株HN基因的ORF全长均为1 716 bp,编码571个氨基酸,符合强毒株的基因长度特征。核苷酸同源性比较显示,2株鹧鸪源NDV分离株与NDV基因XII型同源性高达98.0%～98.1%, 5株斑鸠源和3株鸽子源NDV病毒与NDV基因VI型的同源性高达90.0%～91.9%。遗传进化分析显示,10株广西野鸟NDV分离株与我国经典强毒株F48E9、弱毒疫苗株LaSota和基因VII型NDV(我国目前应用最广的疫苗株基因型)遗传距离较远。     

两广地区2011-2012年H9N2亚型禽流感病毒的HA基因进化分析

为探究两广地区H9N2亚型禽流感病毒(avian influenza virus,AIV)的变异情况及分子流行规律,于2011—2012年从该地区发病鸡群中共分离到16株H9N2亚型AIV,并对分离株HA基因进行测序与进化分析。结果表明,分离株HA基因开放阅读框全长均为1 683bp,编码560个氨基酸;HA基因核苷酸同源性为88.7%⁹9.6%,编码氨基酸同源性为91.8%99.6%,编码氨基酸同源性为91.8%⁹9.5%。本试验分离毒株与国内疫苗株(GD-SS、SH-F和SD-6)的核苷酸同源性在90.1%99.5%。本试验分离毒株与国内疫苗株(GD-SS、SH-F和SD-6)的核苷酸同源性在90.1%⁹2.6%之间,推导的氨基酸序列同源性在91.6%92.6%之间,推导的氨基酸序列同源性在91.6%⁹4.8%之间。进化分析显示分离株可分为Group 1和Group 2两个亚分支,与疫苗株均属于欧亚谱系的Y280分支,但亲缘关系较远。分离株HA蛋白裂解位点附近序列有3种形式:PARSSR↓GLF、PSRSSR↓GLF和PARLSR↓GLF,均无连续碱性氨基酸的插入,符合低致病性AIV的特征。本试验发现分离株GD4、GX2在HA1的127、295位分别增加一个潜在的糖基化位点;除分离株GD5和GD6外,其余分离株在HA1的216位发生Q216L氨基酸突变,表明其存在感染人的可能性。     

羊口疮病毒上海流行株的分离鉴定及其保护性抗原基因遗传进化分析

为了解上海地区羊口疮病毒(ORFV)流行毒株的分子生物学特性与遗传变异情况,采集疑似ORFV感染的羔羊唇部结痂组织,应用PCR、MDBK细胞分离培养、电子显微镜观察、间接免疫荧光技术等方法,进行分离鉴定,并对这2个分离毒株保护性抗原基因F1L、B2L进行克隆与序列分析。结果表明,成功分离到2株ORFV,将其分别命名为ORFV-F416、ORFV-F429。其中,2株分离株F1L基因与参考毒株核苷酸序列同源性分别为95.2%~99.4%,推导氨基酸序列与参考毒株氨基酸序列同源性分别为94.4%~99.4%,遗传进化树分析均显示2株均属于同一分支,且与福建株FJ-YX(KC568410)亲缘关系最近。但与相关参考毒株相比,分离株FIL基因编码的氨基酸在44~66位不存在核苷酸的缺失,表明上海流行株与FJ-YX株存在一定的变异。2株分离株B2L基因与参考毒株核苷酸序列同源性为96.7%~99.6%,氨基酸序列同源性为94.7%~98.9%,且在遗传进化树上均与广西株GX-YB(JQ904793)有较近的亲缘关系,但与中国疫苗株(JQ904789)亲缘关系较远。表明从上海地区分离得到的2个毒株与流行于中国南方地区的ORFV毒株有较近的亲缘关系,但分离株的FIL基因和B2L基因存在一定变异。     

蓝舌病病毒血清1型野毒株及疫苗株S10基因差异

蓝舌病病毒血清型 1型是主要致病血清型之一。为明确其流行规律的分子生物学基础 ,采用 RT- PCR扩增和序列测定技术分析了 15株野毒株及 1株弱毒疫苗株的 S10全基因片段 ,并对其核苷酸和氨基酸差异进行了比较。所有毒株 S10基因核苷酸长度均为 82 2 bp,含有 2个起始密码子 (核苷酸 2 0～ 2 2和 5 9～ 6 1)和 1个终止子 (核苷酸 70 7～70 9) ,预测编码 2种蛋白 (NS3和 NS3A)。不同毒株间 S10基因核苷酸差异为 0～ 138个 (同源性 10 0 %～ 82 %) ,NS3/NS3A蛋白氨基酸差异为 0～ 15个 (同源性 10 0 %～ 93%)。基于 S10基因序列分析 ,可将蓝舌病病毒野毒株及疫苗株分为 2个基因群 :12株野毒株及 1株疫苗株为基因 群 ,3株野毒株与澳大利亚 型毒株属于基因 群 ,两群间的核苷酸同源性为 79%。各基因群在地域分布及宿主来源上未发现有明显的特征性。基因群与毒株分离年代、对 BHK- 2 1细胞毒力等特征关系亦不明显。     

2012-2014年河南省猪伪狂犬病病毒gE基因和TK基因的遗传变异分析

为了解河南地区猪伪狂犬病病毒(PRV)流行株的遗传变异情况,本研究对2012-2014年14株河南PRV分离株的2个主要毒力基因gE和TK进行扩增、克隆测序和遗传进化分析。结果显示:14株河南分离株的gE基因氨基酸同源性为95.7%~99.8%,与2012年之前国内分离的毒株同源性较低(96.6%~98.9%),并在多个部位存在碱基的插入与替换,与2012年之后中国流行的毒株的同源性较高(除XX1外同源性为98.7%~99.5%);14株TK基因的氨基酸同源性为98.1%~100.0%,与疫苗株Bartha株同源性为98.1%~99.4%,与2012年之后流行株的氨基酸同源性为98.4%~99.7%。进化树分析显示:PRV流行毒株gE基因和TK基因均可分为3个群,与国内分离的大多数毒株同处于基因1群。分析结果表明:14个分离株与ZJ-01株、TJ株亲缘关系较近,与Ea株、Min-A株、LA株次之,与Becker株、Kaplan株和P-Prv株亲缘关系较远。TK基因较为保守,gE基因存在很多点突变,提示可能是当前流行毒株毒力增强从而导致当前疫苗免疫保护力下降的主要原因。     

鸽新城疫病毒北京分离株F基因的遗传进化分析

对一株分离自北京市的鸽源新城疫病毒BJP13株的F基因进行扩增、序列测定和分析。结果显示,F基因核苷酸序列长为1 662bp,编码553个氨基酸,蛋白裂解位点的序列为112RRQKRF117,具备强毒株的序列特征;同源性比较显示,BJP13与国内外不同基因型毒株的同源性在87.9%~99.1%;与新城疫基因Ⅵ型的同源性较高,为93.7%~99.1%,其中与基因Ⅵb亚型中的毒株11和毒株LLN713同源性最高为99.1%,与1996年北京分离株STP96的同源性最低为93.7%;与基因Ⅰ型疫苗株V4株和基因Ⅱ型疫苗株La Sota株的同源性分别为90.3%和88.6%;遗传进化分析显示,北京分离株BJP13与比利时毒株11、4940和中国毒株SDS、LLN713最为接近,位于同一进化分支上,属于基因Ⅵb亚型。     

VP2‐segment Sequence Analysis of Some Isolates of Bluetongue Virus Recovered in the Mediterranean Basin During the 1998–2003 Outbreak

The complete nucleotide sequences of the VP2 segments of bluetongue virus (BTV) isolates recovered from Italy, Greece and Israel, from 1998 to 2003, were determined. Phylogenetic analysis of these sequences, those from related viruses and the South African vaccine strains, were used to determine the probable geographic origin of BTV incursions into Italy. Results indicated that viruses from each of the four serotypes isolated in Italy (2, 4, 9 and 16) possibly had a different origin. Analysis of the bluetongue virus serotype 2 (BTV‐2) isolates gave evidence that this serotype probably moved from Tunisia. BTV‐4 results showed probable incursion from the southwest and not from Greece or Israel. BTV‐9 isolates clearly have an eastern origin (most probably Greece), whereas BTV‐16 isolates are indistinguishable from the BTV‐16 live attenuated vaccine strain. The phylogenetic findings were supported by polyacrylamide gel electrophoresis (PAGE) analysis of the complete amplified genome of each isolate except for BTV‐16 Italian field isolate, which showed a slightly different PAGE profile. A combination of the complete VP2 sequencing and PAGE analysis of complete genomes, allowed not only phylogenetic analysis, but also vaccine detection and assessment of reassortment events.     

VP2-segment sequence analysis of some isolates of bluetongue virus recovered in the Mediterranean basin during the 1998-2003 outbreak

The complete nucleotide sequences of the VP2 segments of bluetongue virus (BTV) isolates recovered from Italy, Greece and Israel, from 1998 to 2003, were determined. Phylogenetic analysis of these sequences, those from related viruses and the South African vaccine strains, were used to determine the probable geographic origin of BTV incursions into Italy. Results indicated that viruses from each of the four serotypes isolated in Italy (2, 4, 9 and 16) possibly had a different origin. Analysis of the bluetongue virus serotype 2 (BTV-2) isolates gave evidence that this serotype probably moved from Tunisia. BTV-4 results showed probable incursion from the southwest and not from Greece or Israel. BTV-9 isolates clearly have an eastern origin (most probably Greece), whereas BTV-16 isolates are indistinguishable from the BTV-16 live attenuated vaccine strain. The phylogenetic findings were supported by polyacrylamide gel electrophoresis (PAGE) analysis of the complete amplified genome of each isolate except for BTV-16 Italian field isolate, which showed a slightly different PAGE profile. A combination of the complete VP2 sequencing and PAGE analysis of complete genomes, allowed not only phylogenetic analysis, but also vaccine detection and assessment of reassortment events.     

Molecular epidemiology of bluetongue virus in Portugal during 2004-2006 outbreak

After 44 years of epidemiological silence, bluetongue virus (BTV) was reintroduced in Portugal in the autumn of 2004. The first clinical cases of bluetongue disease (BT) were notified in sheep farms located in the South of Portugal, close to the Spanish border. A total of six BTV, five of serotype 4 and one of serotype 2 were isolated from sheep and cattle during the 2004-2006 epizootics. The nucleotide sequence of gene segments L2, S7 and S10 of BTV-4 prototype strain (BTV4/22045/PT04) obtained from the initial outbreak and of BTV-2 (BTV2/26629/PT05) was fully determined and compared with those from other parts of the world. The phylogenetic analysis revealed that BTV4/22045/PT04 is related to other BTV-4 strains that circulate in the Mediterranean basin since 1998, showing the highest identity (99%) with BTV-4 isolates of 2003 from Sardinia and Corsica, whereas BTV2/26629/PT05 is almost indistinguishable from the Onderstepoort BTV-2 live-attenuated vaccine strain and its related field strain isolated in Italy. Since live-attenuated BTV-2 vaccine was never used in Portugal, the isolation of this strain may represent a natural circulation of the vaccine virus used in other countries in Mediterranean Europe.     

猪瘟病毒野毒株和兔化弱毒疫苗株RT-PCR-RFLP鉴别检测方法的建立

本研究旨在建立猪瘟病毒野毒株和兔化弱毒疫苗株RT-PCR-RFLP鉴别检测方法。根据Shimen株设计1对特异性引物,建立猪瘟病毒RT-PCR-RFLP检测方法;对20份疑似猪瘟临床样品进行检测,并对检出的山东8株流行野毒株和2株疫苗株PCR产物进行克隆与序列分析,验证上述方法。结果RT-PCR扩增片段为825bp,产物经RFLP分析,野毒株的PCR产物能被ApaⅠ酶切为322bp和503bp 2个片段,兔化弱毒疫苗株则不能被酶切,检测出RNA的最低浓度为0.028 6μg.mL-1;8株流行野毒株都含GGGCCC序列(ApaⅠ酶切位点),2株疫苗株相应序列为GAGCCC,不能被ApaⅠ酶切;8株流行野毒株属于基因2群,2株疫苗株与HCLV遗传关系近,为基因1群。建立了可鉴别猪瘟病毒野毒株和兔化弱毒疫苗株RT-PCR-RFLP检测方法,为猪瘟的防控提供有效手段。     

Comparison of genome segments 2, 7 and 10 of bluetongue viruses serotype 2 for differentiation between field isolates and the vaccine strain

Bluetongue (BT) virus serotype 2 (BTV 2) was first confirmed in Tunisia in February 2000 and has since spread northward and westward, infecting several other countries and islands, including Corsica, where clinical disease was reported in October 2000. BT was again reported on the Island in July 2001, some six months after a vaccination campaign against BTV 2. The molecular relationship between isolates of the BTV 2 Corsican wild-type viruses from 2000 and 2001, and the attenuated BTV 2 vaccine were determined by comparing corresponding sequences of genome segments 2, 7 and 10 with each other and with already published sequences available in the genome database. Complete genetic stability was observed between the isolates of the Corsican BTV 2. There was some divergence between the nucleotide sequences of segment 10 obtained from the wild-type and vaccine virus strains. Based on these differences, primers were selected that could be used in RT-PCR to differentiate between the wild-type and the vaccine viruses.     

IBV D41株主要结构基因及3′端非编码区序列分析

采用反转录及聚合酶链式反应 ( RT-PCR) ,成功地扩增出鸡传染性支气管炎病毒 ( IBV)人工致弱毒D41株 S1基因、M基因、N基因和基因组 3′端非编码区 ( U TR)的 c DNA。序列测定结果表明 :D41株的 S1基因全长 1611bp(从 ATG到 S前体蛋白裂解位点 ) ,编码一条由 53 7个氨基酸组成的多肽 ;M基因全长 678bp,编码一条由 2 2 6个氨基酸组成的多肽 ;N基因全长 12 3 0 bp,编码一条由 410个氨基酸残基组成的多肽 ,3′端 UTR长度为52 5bp,其中高变区 ( HVR)长度为 2 2 5bp。与国内外已报道的一些 IBV标准毒株的相应基因序列进行核苷酸序列同源性分析后发现 :D41株与麻省血清型的毒株同源性最高 ,尤其与国际常用的标准疫苗株 H52和 H12 0的亲缘关系最接近。但它与国内“腺胃型”毒株 QXIBV在系统发生进化树上却相隔较远     

Differentiation between field and vaccine strain of bluetongue virus serotype 16

In August 2000, bluetongue virus (BTV) appeared for the first time in Sardinia and, since then, the infection spread across Sicily and into the mainland of Italy involving at the beginning serotypes 2 and 9 and then, from 2002, 4 and 16. To reduce direct losses due to disease and indirect losses due to new serotype circulation, the 2004 Italian vaccination campaign included the modified-live vaccines against BTV-4 and 16 produced by Onderstepoort Biological Product (OBP), South Africa. Few months after the end of the campaign, BTV-16 was reported broadly in the country and the need of differentiating field from the BTV-16 vaccine isolate became crucial. In this study, the gene segments 2, 5, 6 and 10 of both the Italian and vaccine BTV-16 strains were sequenced and their molecular relationship determined. As sequences of segment 5 were those showing the highest differences (17.3%), it was possible to develop a new diagnostic tool able to distinguish the Italian BTV-16 NS1 gene from that of the homologous vaccine strain. The procedure based on the use of a RT-PCR and the subsequent sequencing of the amplified product showed a high degree of sensitivity and specificity when samples from either BTV-16 vaccinated or infected sheep were tested.     

Recombinant cDNA probe from bluetongue virus genome segment 10 for identification of bluetongue virus

Genome segment 10 of bluetongue virus (BTV) serotype 11 UC8 strain was cloned and subsequently hybridized to viral double-stranded RNA extracted from 90 field isolates of BTV serotypes 10, 11, 13, and 17; the prototype strains of BTV 2, 10, 11, 13, and 17; the prototype strain epizootic hemorrhagic disease virus (EHDV) serotype 1; and 4 field isolates of EHDV serotype 2. The 90 field isolates were obtained from different counties in California, Louisiana, and Idaho during the years 1979, 1980, and 1981. The cloned genetic probe hybridized with all the BTV samples tested, showing different degrees of cross-hybridization at the stringency conditions used in this study. This indicated that BTV genome segment 10 has conserved nucleotide sequences among the BTV serotypes 2, 10, 11, 13, and 17. No cross-hybridization signals were detected between the cloned genome segment 10 of BTV 11 UC8 strain and the prototype strain of EHDV serotype 1 and the field isolates of serotype 2. This probe recognized a wide variety of BTV isolates.     

The detection of the meq gene in chicken infected with Marek's disease virus serotype 1

In the genome of strains of very virulent Marek's disease virus serotype 1(vvMDV1), such as Md5 and RB1B, the meq open reading frame (ORF) encoding a 339-amino-acid bZIP protein, is present, while a slightly longer meq ORF, termed as L-meq, in which a 180-bp sequence is inserted into the meq ORF is found in other strains of MDV1, such as CV1988/R6 and attenuated JM. When chickens were infected with vvMDV1 strains and the meq gene was amplified by nested polymerase chain reaction (PCR), the meq gene was detected throughout the experimental period for 7 weeks post inoculation (pi). However, the L-meq gene was also detected at 3 to 5 weeks and 3 to 4 weeks pi. in Md5-infected and RB1B-infected chickens, respectively. In the case of chickens infected with an attenuated MDV1, the JM strain, the L-meq gene was detected at 2 to 7 weeks pi., and the meq gene was also detected at 2 to 6 weeks pi. Both L-meq and meq genes were detected in chickens infected with an attenuated nononcogenic vaccine strain of MDV1 (CVI988/R6), throughout the experimental period. Though quantitative PCR was not performed, a larger amount of the PCR products corresponding to the L-meq than the meq gene was amplified from chickens infected with JM or CVI988/R6. These results suggest that a dynamic population shift between the MDV subpopulations displaying meq and L-meq genes occurs in chickens during the course of MDV infection. Since the MDV subpopulation that displays the L-meq gene only displays it during the latent phase, the L-meq and its gene product, if any, might contribute to the maintenance of the MDV latency.