| Newcastle disease, caused by Newcastle disease virus (NDV), is one of the most serious diseases of poultry that has caused heavy losses in many countries. NDV is the unique member of avian paramyxovirus serotype-1 (APMV-1). The pathogenicity of NDV to different hosts has crucial distinction. Chicken is the most sensitive host, other fowls such as pigeon also can be infected and be taken bad, however, waterfowls such as goose and duck have strong resistibility for NDV. The waterfowls can be infected by NDV, but they don't show apparent clinical symptoms generally. They only act as the carriers of virus. Goose paramyxovirus (GPMV) disease is highly infectious and has caused frequent outbreaks from 1997 in China. The disease has high incidence and mortality rates to poultry. An acute and violent disease was outbreak in goose flocks in Shanghai in 1999. The virus isolate was designated as SF02 and identified as the causal agent of the outbreaks. GPMV was identified to be a member of avian paramyxovirus-1 (APMV-1). However, a significant difference exists between GPMV and NDV in the host pathogenicity. The NDV is generally pathogenic only to fowl, such as chicken and pigeon, while SF02 is highly pathogenic to both fowl and waterfowl, such as chicken, pigeon, partridge, goose and duck.The present study involves:Part I. It has been shown that there is a significant difference between the host pathogenicities of NDV and GPMV in animal. We investigated whether there is any difference of the pathogenicities in culture cells. Chicken and goose embryo fibroblasts were infected with NDV strains F48E9 (velogenic), Komarov (mesogenic), La Sota (lentogenic), V4/66 (avirulent) and GPMV SF02. The results shown that there is not significant distinction between the pathogenicity of NDV and GPMV to embryo fibroblasts.Part II. In order to elucidate the reason of the pathogenicity difference, the complete genome of SF02 was cloned by RT-PCR, Ligation-anchored PCR and analyzed by computer programs. The entire genome consists of 15 192 nucleotides. The genomes of SF02 isolate and of NDV strains contain 6 common ORFs in the same order: 3' -NP-P-M-F-HN-L- 5', but SF02 genome has extra 6nt between NP and P genes. Moreover, an antisense ORF at the 1960 to 1412 is found in the genome of SF02, but it is absent in NDV genomes. The genome of SF02 shares above 80% identities with NDV strains. Molecular phylogenetic analysis shows that the SF02 is a member of NDV genotype VIIa. Based on the molecular analysis of genomes of SF02 and NDV, the possible mechanism causing different host pathogenicities is discussed.Based on the sequence of F gene, a multiplex RT-PCR method has been developed. It could be used for the discrimination of GPMV from NDV.Part III. The virus diseases are being a great challenge for human health. Ribozyme is an effectively potential therapy scheme. In this study, hammerhead ribozyme RzF598 and its dysfunctional mutant dRzF598 targeting to the F gene of goose paramyxovirus SF02 have been designed. The transgenic plasmids pcDNARzF598 and pcDNAdRzF598 were constructed by inserting ribozyme genesinto eukaryotic expression vector pcDNA3. The plasmid pcDNA3 that lacks full ribozyme gene was used as a control. Plasmids pcDNARzF598, pcDNAdRzF598 and pcDNA3 were transfected into chicken embryo fibroblasts (CEFs). The concentration of virus released by infected CEFs and the survival rates of CEFs were identified. The results indicated that RzF598 successfully suppressed the replication of SF02 in CEFs. Survival rate of CEFs being transfected with pcDNARzF598 and infected SF02 was above 80%, while the survival rates of untransfected CEFs and CEFs transfected with pcDNA3 after infection with SF02 were only about 5 %.Based on this dissertation, the knowledge about the mechanism causing the host pathogenicity difference between NDV and GPMV was much more elucidated, and the possibility of using hammerhead ribozyme for the therapy of the disease causing by SF02 virus was investigated.
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