摘要
网状内皮增生症病毒(Reticuloendotheliosis virus, REV)、马立克氏病病毒(Marek’s disease virus, MDV)、鸡传染性贫血病病毒(Chicken anemia virus, CAV)和J亚群白血病(Avian leukosis virus subgroup J)是目前鸡群中常见的免疫抑制性病毒。这些病毒除不同程度的引起机体发生原发感染之外,更严重的是以继发感染的形式出现,致使家禽的免疫系统受到损害,引起机体免疫功能下降,导致疫苗免疫效果降低。根据近年的报道,种鸡和商品鸡均存在这些病毒的感染,并存在不同程度的共感染;发病鸡群新城疫等抗体水平明显偏低的原因多数是由于鸡群感染免疫抑制性病毒所致;种鸡群感染并垂直传播给商品鸡,间接引起了商品鸡群30日龄左右免疫能力降低,死亡率上升。因此,免疫抑制性疾病是目前养鸡业的潜在威胁,给养鸡业造成了巨大的经济损失。
1. REV、ALV、MDV和CAV在山东省肉鸡群中感染状况的调查
从山东省潍坊、青岛、泰安三个地区30个疑似免疫抑制性疾病感染鸡群中采集948只鸡的脾脏,用组织DNA直接斑点杂交方法检测各样品中REV、MDV、CAV的感染状况。同时采集各个鸡只的泄殖腔棉拭子,用酶联免疫吸附试验检测禽白血病病毒p27抗原。结果表明:所有鸡场中ALV感染率(52.7 %)最高,其次为REV(46.3%)。各地区都存在非常严重单独感染和混合感染,并且感染率从种鸡到商品鸡呈递增趋势。潍坊地区ALV发病最频繁,REV在青岛地区感染率最高。REV、MDV、ALV和CAV的广泛传播和多重感染是当前山东省各鸡场条件性致病菌发病率高、家禽生产性能下降的重要原因。
2.由疫苗污染所致规模化鸡场免疫抑制性疾病的垂直传播
用间接免疫荧光检测出山东某规模化AA祖代鸡场所用的疫苗中有两株疫苗感染REV,一株感染ALV-J。该祖代鸡下属父母代鸡场和商品鸡场所用疫苗没有出现这种现象。随即采集该祖代鸡场的27周龄祖代鸡及其所生产的19日龄父母代鸡胚、25周龄父母代鸡及其所生产的19日龄商品代鸡胚、1日龄商品鸡和30日龄商品鸡的脾脏样品,采用斑点杂交方法调查各代次鸡群中REV、MDV、CAV的感染状况,同时用酶联免疫吸附试验检测各样品中ALV-J抗体阳性率。结果表明:祖代种鸡中REV、ALV-J分别为13.1%和10.8%,未出现MDV、CAV感染,其所生产的19日龄父母代鸡胚REV感染率为11.3%;父母代鸡中REV、CAV、ALV-J分别为16.2%、10.8%和21.6%,30日龄商品鸡中这三种病毒的检出率分别为34.6 %、14.1%和42.3 %;父母代鸡所生产的商品代鸡胚中REV、CAV的检出率分别为24.5%和14.2%,REV和CAV的共感染率为11.3%。在父母代鸡中存在REV和ALV-J的共感染(13.5%)以及REV和CAV的共感染(8.1%);二重感染在商品鸡中也很严重REV+ALV-J (26.9%)、REV+CAV(9.0%)、CAV+ALV-J(11.5%)。鸡群这几种病毒单独感染和混合感染的感染率从父母代种鸡到商品鸡呈增长趋势。可见REV和ALV-J在祖代种鸡、父母代鸡再和商品鸡中的广泛传播与祖代鸡厂接种污染这两种病毒的疫苗有关,然后在鸡群中垂直传播。
3. AA肉种鸡内源性类ALV-J gp85基因及其抗原表位的分析
利用ALV-J gp85基因两侧的序列片段为引物,从山东潍坊某肉种鸡场送检的7日龄肉种鸡的基因组中完整地扩增了内源性类ALV-J gp85基因。利用ALV-J env基因特异性引物不能扩增出长度为2.2kbp的目的片段,用ALV-J特异性单抗JE-9做间接免疫荧光检测,也呈现阴性反应。这种内源性类ALV-J gp85基因与已报道的禽内源性反录病毒EAV-HP序列的同源性为85.6 %～93.8%。所得到的内源性类ALV-J gp85基因与外源性ALV-J毒株HPRS-103、SD07LK1、NX0101的同源性分别为93.8%、91.8%、91.7%。并且与外源性ALV-J gp85基因具有相似的Jameson-Worlf抗原表位优势。这种内源性类gp85基因很可能与肉雏鸡早期感染ALV-J后所呈现的免疫耐受现象有关。
Reticuloendotheliosis virus (REV), Marek’s disease virus (MDV), Chicken anemia virus (CAV) and Avian leukosis virus subgroup J (ALV-J) were the major immunosuppressive virus in current chicken flocks. These immunosuppressive virus can cause primary infection in different extent. Even more, these virus can make other pathogens easily infected, and then make chicken immunity descend, chicken body immunosuppressive and effect of vaccine fall. Current reports showed that these virus existed in the investigated chicken flocks and Co-infections were serious. The infections of immunosuppressive virus were the main causation for descent or failure of the function of the NDV vaccines. The breeder flocks were infected by them and then the 1d chicken flocks were infected vertically which made the death rate of 30d commercial chicken flocks increase. So infections of immunosuppressive virus were the potential menace to poultry industry at present, and bring mass economic loss for poultry industry at present.
1. Epidemic Investigation of infection of REV, ALV, MDV and CAV in meat-type flocks in Shandong province
The tissues samples were collected from 948 birds in 30 chicken flocks wich suspected to be infected by immunodepressive virus in Weifang, Qingdao and Taian of Shandong province. The DNA was extracted for hybridizationin Dot-blot with probes of Reticuloendotheliosis virus (REV), Marek’s disease virus (MDV) and Chicken anemia virus (CAV). At the same time, we investigated Avian leukosis virus subgroup p27-shedding in cloaca swabs from collected birds using ELISA method. The result indicated that these virus existed in the investigated chicken flocks and co-infections were serious. Single infection and co-infection increased by degrees from broiler breeders to commercial chicken in diseased farms. Weifang was detected as the region where occur ALV frequently most of all. The checkout ratios of REV in Qingdao Region is higher than other regions. The result indicated that existing in wide range and co-infection of REV, MDV, ALV and CAV in chickens are the important causations for high incidence opportunistically pathogenic diseases and descent of poultry production performance in Shandong province.
2. Vertical Transmission of Immunosuppressive diseases in large-scale AA Broiler Breeder caused by Contaminated Vaccines
The Indirect immunofluorescence analysis (IFA) was applied to check vaccines which have been vaccinated to grandparent generation breeding birds in one large-scale AA broiler breeder company of Shandong province. There are two vaccines contaminated by REV and one contaminated by MDV used in grandparent generation broiler breeders according to indirect immunofluorescence analysis. This phenomenon didn’t appear in vaccines used in their corresponding broiler parent flocks and commercial flocks. The tissues samples of 27 weeks grandparent generation breeding birds and their 19 days incubating embryos, 25 weeks broiler parent flocks and their corresponding 19 days incubating embryos, 1 days and 30 days commercial chicken were randomly collected. To detect REV, MDV and CAV by dot-blot hybridization with tissue-extracted DNA as the templates. At the same time, serum were collected from all birds for investigating the infection of Avian leukosis virus subgroup J (ALV-J) using ELISA method. The checkout ratios of REV and ALV-J in the grandparent generation breeding birds were 13.1% and 10.8%, not occur infection of MDV and CAV, the checkout ratios of REV in their 19 days incubating embryos was 11.3%. The infection rate of REV、CAV and ALV-J were 16.2%、10.8% and 21.6% in broiler parent flocks, and in the 30 days commercial chicken the infection rate of REV、CAV and ALV-J were 34.6 %、14.1% and 42.3 %. In 19 days incubating commercial embryos, the infection rate of REV、CAV were 24.5% and 14.2%, the dual infection of this two virus were 24.5%. Dual infection of REV+ALV-J(13.5%) and REV+CAV (8.1%) was occured in the broiler parent flocks. Dual infection in the 30 days commercial chicken were serious: REV+ALV-J (26.9%), REV+ CAV(9.0%), CAV+ALV-J(11.5%). The checkout ratios of single infection and dual infection increased by degrees from broiler breeders to commercial chicken. The results indicated that REV and MDV transmit widespread in this broiler breeders may originally come from routine vaccines contaminated by REV or MDV, and then transmisted generation by generation in chicken flocks.
3. Analysis of Avian Endogenous ALV-J gp85-like Gene and it’s Epitope in AA Meat-type Broiler Breeder
primers corresponding to the nucleotide sequences flanking the ALV-J gp85 gene were used to amplify the intact endogenous gp85-like gene from 7 days AA meat-type broiler breeder collected in Weifang region Shandong province. The isolate strain was negative reaction in polymerase chain reaction with specific primers of ALV-J env gene and gave nothing reaction in indirect fluorescence antibody assay(IFA)with ALV-J specific monoclonal antibody JE-9. The endogenous ALV-J gp85-like gene had 85.6% to 93.8% homology with the Endogenous avian retrovirus haemangiopericytoma (EAV-HP) sequences have been reported. The endogenous ALV-J gp85-like elements demonstrated 93.8%, 91.8% and 91.7% identical to strain HPRS-103、SD07LK1、NX0101 ALV-J. Antigenic index analysis indicated that ALV-J gp85-like of meat-type broiler breeder was highly similar to that of exogenous ALV-J. The endogenous ALV-J gp85-like gene may play a important role in immunological tolerance of chick after infected with ALV-J.
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