Research On Reticuloendotheliosis Virus Contamination Of Wild Type Fowlpox Virus And Fowlpox Vaccine

It has become a common phenomenon that REV gene fragments integrated into FPV vaccines, gene fragments and even complete genome integrated into the FPV wild strains.Studies have shown that, the development of FPV and REV integration has promotion effect on Pox virus proliferation and infection. And this integration has great influence on the biological characteristics of FPV. The most obvious manifestation is the decreased FPV vaccine protection force and the enhancement of wild virus virulence.In this study, REV integration was isolated for identification and sequence comparison from 12 different PFV vaccine batches from different regions and abroad during 2012-2014,three turkey pox and one chicken pox from a region of Tai’an. In order to estimate the defects of PFV vaccines used currently, the potential risks as well as REV Pollution in PFV at home and abroad.12 fowl pox vaccine strains were inoculated to CEF and passaged until obvious cytopathy appeared, and then extracted cell DNA. According to the published integration sequence, PCR amplified FPV-REV 5,LTR integration area. Meanwhile, amplified the sequences of LTR, Env, Gag, Pol fragments of REV.The results showed that, the products containing REV 5,LTR and FPV fragments were amplified in the 12 fowl pox vaccine strains,but the sequences of Env, Gag and Pol were not amplified. Etermined the sequence of FPVREV 5,LTR integration by NCBI, DNA-star comparative analysis. Two foreign vaccine strains integrated with 446 bp REV-LTR sequences, and the homology with REV wild strain HA9901 isolated recent years in China was 98% and 94.3% with SNV.REV-LTR fragments of another 10 domestic integrated vaccine strains are relatively small, only 194 bp, and the homology with HA1101 was only 98.4% and 96.4% with HA9901. The homology between the integration zones of the 10 domestic vaccine strains and published abroad fowl pox strain AY255632 and HP-438 was as high as 98.6%-100%. And the homology between two foreign vaccine strains and AY255632 was 100%. The results showed that the detected 12 fowl pox vaccine strains were partly integrated with REV LTR sequence, and the homology with isolates from America is higher than the isolates from China.Three turkey pox and one chicken pox wild strain were serially passaged with chick embryo until variola appeared. The results showed that, the products containing REV 5,LTR and FPV fragments were amplified in the four wild virus, and the sequences of Env, Gag and Pol were amplified too.The sequence analysis showed that the homology of the FPV-REV 5,LTR integration in the four wild strains is 100%, and is highly homologous with the integration areas of domestic vaccine strains.At the same time select T1 strain infected 20 SPF chickens, and detected REV antibodies by ELISA method. The positive rate of REV antibody was 0% before poison attack, and the positive rate was 100% after two weeks of poison attack.Dissected the chickens, there were general pathological changes in the immune organs and other organs, including bursal bleeding and atrophy, thymus bleeding and atrophy,tracheal bleeding associated with mucilage, kidney swelling and other symptoms,it may caused by REV but needs further study.Protected SPF chickens by PFV vaccines(two Chinese vaccine strains, a foreign vaccine strain) integrated with REV-LTR from three different manufacturers. Infected birds with FPV wild strain integrated REV genome. The results showed that the protective immunity of the three vaccine strains reached 100%(incidence rate were 20/20, 26/26, 15/15),the incidence rate was 85% in the control group(18/21).