| Newcastle disease(ND)is a highly contagious disease caused by Newcastle disease virus(NDV),which mainly infects poultry,it has harmed the development of poultry industry in China and the world for a long time.Though the prevalence of Newcastle disease has slowed down in recent years,the host range of it is still expanding and the new genotypes are also constantly emerging.Therefore,it is of great significance to carry out NDV phylogeography research and to build a risk assessment model for NDV infection in poultry farms for ND control.The main content of this project was displayed as the follows:1.Genetic diversity of Newcastle disease virus and phylogeography of its predominant genotypes in China.In this study,the prevalence of NDV in China was investigated in recent years,and the F and HN gene sequences during 1986 to 2015 of NDV in China were collected from Gen Bank for the first time.Based on the Bayesian phylogeography,the genetic diversity,the migration links between diverse regions and the potential transmission risk between poultry and wild birds in China were inferred.The results showed that the overall outbreaks of NDV in China have been declining in recent years,and its genetic diversity is also no longer growing.The mean evolutionary rates of the F genes of genotype ? and ?,and HN gene of genotype ?,were estimated at 8.07×10-4 subs/site/year(95%HPD:5.06×10-4?1.09×10-3),1.03×10-3subs/site/year(95%HPD:8.54×10-4?1.19×10-3)and 8.78×10-4 subs/site/year(95%HPD:7.11×10-4?1.05×10-3),respectively.Phylogeography analysis showed that the origin region of each genotype of NDV may be different.Genotype ? may originate in Jiangxi Province at first,and genotype ? in Guangxi Province.It is speculated that the Province of Shandong and Jiangsu are the most likely transmission centers of NDV in China.In the future,we should focus on monitoring and control these areas to reduce the risk of cross provincial spread of NDV.In addition,sporadic cases of Nd in wild birds may be mainly spilled from poultry.Migration of wild birds seems to play a weak role in the spread of NDV in poultry.2.The research of the risk assessment model of NDV infection in scale poultry farm.The risk assessment model of NDV infection in large-scale poultry farms was established by Delphi method and AHP.The risk assessment model has a total of 43risk factors,among which 3 are the special priority items:NDV was detected as virulent strains in chicken farm,no vaccine inoculation in this field,and there are Newcastle disease epidemic within 1000m upwind of chicken farm.After the model was established,the scale of poultry farms in southwest China was evaluated through field visits and questionnaire surveys.The results showed that the 51 large-scale poultry farms surveyed were all evaluated as low-risk and moderate-risk,and no high-risk situations occurred.Among them,the risk assessment level of large-scale chicken farms is all evaluated as low risk,the risk assessment level of medium-sized chicken farms is low risk accounting for about 85%,medium risk accounting for 15%;the risk assessment level of small-scale farms is low risk accounting for only 6%,medium risk accounting for 94%.However,there are still big loopholes in the planning and layout,feeding management,harmless treatment and disinfection,monitoring of immune antibody level and disease purification of the small-scale chicken farm,which should be improved in the future.The assessment results show that the current large-scale poultry farms in Southwest China pay more attention to NDV control and the risk of Newcastle disease outbreaks in these regions is low.In this study,phylogeography analysis of F and HN genes of NDV predominant genotypes in China was carried out to understand the epidemic trend and the origin and migration of virus,providing a basis for ND control.At the same time,the risk assessment model of NDV infection can provide theoretical basis and scientific guidance for the prevention and control of Newcastle disease in poultry farms. |
PDF Full Text Request