Evaluation Of Immune Efficacy Of Newcastle Disease Recombinant Virus RmNA-1 As A Vaccine Candidate Strain

Newcastle disease is one of the most serious diseases in China's poultry industry,and the control or research about Newcastle disease has always attached great importance in the world.Studies have shown that genotype ? has become dominant during the prevalence of ND in China.However,the extensive use of attenuated ND vaccines(such as La Sota)still focused on genotype II.Though protection against morbidity or mortality can be offered by genotype II vaccines,it presents tissue or organ lesions among chicken immunized with this kind of vaccines.The use of vaccines of the same genotype as the epidemic strain not only reduces the chance of spreading viruses into the outside,but also significantly reduces the viral load in the laryngeal and cloaca.Therefore,it is necessary to use vaccines consistent with the epidemic genotype in an attempt to prevent ND effectively.In a situation like this,It is necessary to develop new attenuated ND vaccines of gene type VII.In this study,rm NA-1,a recombinant mutant strain of Newcastle disease,was used as vaccines.During the subculture in chicken embryos or chicken,genetic stability,immunological safety and immunological efficacy of the vaccines was compared with the most commonly used commercial vaccines of La Sota strain,thus laying the foundation of developing a vaccine candidate consistent with current epidemic strains.With these data,we would be able to complete the project "Newcastle disease diagnosis and prevention and control and demonstration",and aslo it will help to contribute to declaring a new veterinary drug at the Ministry of Agriculture.The main contents are as follows:?.Genetic stability of recombinant virus rm NA-1 strainIn order to determine the genetic stability of the newly reconstituted ND virus rm NA-1 strain,the experiments were carried by two parts: the genetic stability test of chicken embryo and the genetic stability test of the chicken.The recombinant virus survived the 14 th generation on the basis genetic stability in chicken embryo.And the mutant locus remained stable,no mutations occurred,indicating that the mutant rm NA-1 could at least be stable during the chicken embryo inheritance for more than 24 generations.In addition,in order to better determine the stability of the recombinant virus,animal experiments were carried out.The genetic stability of the virus remained stable in chicken after six generations.Therefore,the ?-type mutant strain rm NA-1 has the potential of becoming a new ND vaccine candidate.?.Safety test of the recombinant virus rm NA-1 strainTo ensure the safety of the rm NA-1 strain,ten SPF chicken of 3-day-old were infected with rm NA-1 chicken embryo allantoic fluid 0.2ml(about 100 times the normal dose used).Two weeks later,no chicked developed clinical symptoms of ND,nor tissue lesions,indicating that the vaccine candidate is safe.?.Immunization efficacy test of recombinant virus rm NA-1 strainIn order to determine the minimum immunization dose of the recombinant virus rm NA-1,chicken were inoculated with different virus load,and the survival of each group was measured after three weeks.The minimum immunization dose of rm NA-1 was 5×104EID50.In order to determine the immune effect of rm NA-1 virus,forty SPF chicken of 7-day-old were immunized 2×106EID50 virus load.The level of HI antibody was continuously monitored in the immunization process.At six time points,which there is three weeks,six weeks,Seven weeks days,eight weeks,nine weeks,ten weeks,five immunized SPF chickens of each group were selected randomly for a 105ELD50 NA-1 virus challenge.Results showed that the survival rate at all time points were 100%.The immunological duration of the rm NA-1 virus was determined to be at least 8 weeks.?.A comparison on immunization effect between commercial vaccine of the La Sota strain and the rm NA-1.The level of HI antibody in the recombinant virus group decreased rapidly after the challenge and then increased rapidly.As for the commercial vaccine group,the HI antibody level directly increased.Results showed that when the genotype of epidemic strains and vaccine strains matched,the antibody produced by the vaccine would neutralize the virus,and then produced a immune response in the body.Clinical results and survival rate were almost the same between the two group.However,the weight gained of the commercial vaccine group after immunization was much lower than that of the recombinant vaccine group.The virus spread time from cloacal and oropharyngeal of the commercial vaccine group was longer.The histological sections of the commercial vaccine group showed much seriuous tissue lesion,indicating that the use of vaccines of a non epidemic genotype will not ensure fully protection to the animal.