Screening Of Virulent Strains Of Goose Parvovirus And Preliminary Evaluation Of Virus-like Particle Vaccine

Goose parvovirus?GPV?disease,also known as gosling plague,is a viral infection that infects goslings and young muscovy ducks to cause acute or subacute sepsis.The disease has a wide range of epidemics,high incidence,and high mortality rate of goslings,which has brought huge economic losses to the Chinese waterfowl breeding industry.Traditional inactivated vaccine or attenuated vaccine can't prevent and control the disease well.Therefore,this study plans to build a virus-like particle vaccine of GPV from the current popular virus-like particle vaccine,and evaluate its immune effect to provide a new method for the prevention and control of goose parvovirus.The suspected infections of goslings and geese in multiple geese farms in Jilin Province were collected and carried out virus multiplication culture by using goose embryo allantoic fluid.Then 7 GPV viruses were obtained and the status of virus species was determined by PCR and gene sequence analysis.They were named LY strain,SP strain,ZL strain,PS strain,SY strain,LS strain,and CH strain respectively.The pathogenicity of TCID₅₀,ELD₅₀ and LD₅₀ were determined,and the candidate strains of strong virus vaccine were screened.The results showed that the lethality rate of CH strain was 60%,and the lethality rate of LS strain was 50%.It was the two strains with the highest lethality among the 7 strains of GPV strain.Among the test data of TCID₅₀,ELD₅₀,LD₅₀ and other test data,CH strain and LS strain also showed strong pathogenicity.Therefore,the CH strain and the LS strain were used as vaccine candidate strains of this experiment,and were sent to the Changchun Military Veterinary Research Institute for the preparation of the GPV VLPs vaccine.The GPV virulent CH strain was selected as the challenge strain.The death rate was recorded by each data,and the scoring standard was established to construct a 12-day-old gosling infection model,which laid a foundation for subsequent vaccine evaluation.Twenty-day-old goslings were challenged with CH strain.The experimental group was 800TCID₅₀,1200 TCID₅₀,1600 TCID₅₀,and the control group was non-challenged goslings.The body temperature,weight of the goslings and the situation of death were observed and recorded.The results showed that the animals in each experimental group began to have clinical symptoms such as loss of appetite and apathy on the 3rd day after the challenge.At the same time,the average body temperature began to rise and the body weight began to decrease.On the7th day after the challenge,the experimental scores of the experimental groups were the highest.The comprehensive clinical scores of the 800 TCID₅₀,1200 TCID₅₀,and 1600 TCID₅₀experimental groups were 1 CPI,1.6 CPI,and 2.1 CPI,respectively.The optimal concentration to confirm the half-lethal death of the GEV CH strain infected goslings was 1200 TCID50.In the vaccine evaluation test,six GPV virus-like particle vaccines were prepared corresponding to the GPV structural proteins,which were GPV VLPs.LS VP2 VLPs vaccine,LS VP3 VLPs vaccine,LS-?VP2+VP3?VLPs,CH VP2 VLPs vaccine,CH VP3 VLPs vaccine and CH-?VP2+VP3?VLPs GPV VLPs.According to the routine immunization procedure,all the experimental group vaccines and the control group vaccines were immunized to the animals,and the immune effects were evaluated.The blood of the animals after immunization was collected and the results showed that the two groups with higher humoral and cellular immune antibody content in the experimental animals after 10 days of the third immunization were CH VP3 VLPs vaccine group and CH-?VP2+VP3?VLPs vaccine group?p<0.01?.In the challenge protection experiment,three vaccines,CH inactivated vaccine,CH VP2 VLPs and CH VP3VLPs,were used to immunize the goslings at 1 day and 5 days,respectively,and then the virus was then challenged according to the infection standard of the animal infection model.The results showed that the temperature range and weight loss trend of the experimental group were effectively controlled,and the temperature range and weight loss of CH VP3 VLPs vaccine were the smallest.On the 7th day after the challenge,the comprehensive clinical score of the experimental group was reduced compared with the 7th comprehensive clinical score of the12-day-old gosling infection model.The comprehensive clinical scores of CH inactivated vaccine group,CH VP2 VLPs vaccine group,and CH VP3 VLPs vaccine group were 1.2 CPI,0.6 CPI,and 0.3 CPI,respectively,and the CH VP3 VLPs vaccine group had the lowest mortality rate of only 10%.It was finally determined that the virus-like particle vaccine CH VP3VLPs had the optimal immune effect.