The Influence Of Vaccination On The Evolution Of Newcastle Disease Virus In China And Construction Of A Full-length CDNA Clone Of Newcastle Disease Virus LaSota Strain

Newcastle disease (ND), caused by ND virus (NDV), is one of the most seriousavian contagious virus disease all over the world nowadays. It is also one of the mostserious illnesses of birds in our country. NDV has posed a great threaten to the poultryindustry. Because of the severe nature of the disease and the high mortality rates. NDis included as an Office International des Epizooties list A disease.Many commercial Newcastle disease virus (NDV) live vaccines are widely usedfor preventing infection of chickens from Newcastle disease in China. Theseattenuated live vaccines for mass vaccination is thought to be convenient and effective.Therefore, in China, the immune density and frequency of NDV far surpassinternational level, ND was controlled well as a result of the huge of vaccination area.Howover, in recent years, NDV emerged some new epidemic situation. ND stillbreaks out in those vaccinated flocks even though high titre antibody was produced.And the vaccinated strains are hard to avoid draining into the environment, however,the evolution role of a great quantity of vaccine strains is unknown in NDV. Atpresent, it is not clear whether the scattered vaccine strains have any influence on theenvironment.In this study, phylogenetic and recombination analyses were performed and got aseries of evidences for homologous recombination between NDV strains. Severalmosaics were proposed to be partially descended from vaccine strains. These resultsindicate that vaccines may also play roles in shaping NDV evolution via homologousrecombination. Recombination between vaccines and circulating viruses may causeimmunization failure in some cases. Therefore, appropriate immunization programsshould be adopted in NDV preventive treatment so as to avoid such recombination in clinical as much as possible.It is widely accepted that the recombination rate of negative-sense RNA virus isvery low, so the recombination phenomenon in NDV has not been systematicallystudied. This problem has not been concerned in the use of NDV vaccine. Themechanism of recombination in NDV is unknown. In order to know the influences ofrecombination in NDV biological characters, especially virulence variation, andgenetic diversity of of NDV, it is necessary to establish the experimental system ofNDV homologous recombination, to provide laboratory evidence for NDVrecombination. This study use NDV LaSota, a lentogenic vaccine strain widely usedto prevent Newcastle disease, to establish a reverse-transgenic system of NDV. First,we pretreat NDV LaSota by purification and amplification. Then we design twelvepairs of primers for NDV LaSota to amplify the whole genome, and ultimately gettwelve cDNA sections which cover the whole genome. And then, we clone thesetwelve fragments into the pMD18-T vector and sequence them. We use DNAman, abioinformatic software, to analyse the nucleotide sequence of LaSota and thedistribution of restriction enzyme sites. At last, we construct a full-length cDNA cloneof NDV strain LaSota, pMC18-NDV. This work is an important foundation for thestudy of homologous recombination between NDV LaSota strain and circulatingviruses.