| Avian influenza(AI),especially highly pathogenic AI,is a kind of virulent infectious disease.It is a highly contagious disease caused by avian influenza virus(AIV).AI has spread around the world in a variety of ways,it can infect not only birds,such as chickens,ducks and geese,but also mammals(pigs,horses,etc.)and even humans.And what's more,AI often leads to the death of infected animals and humans.Control of AI has become a common task of human public health.At present,the policy on prevention and control of highly pathogenic AI is divided into two different strategies in the world.One is culling of priority,the use of vaccine is strictly controlled or the vaccine immunity is not supported completely.The other is a combination of vaccination and culling.China has adopted the strategy of vaccination combined with culling.AI has been well controlled in China since 2004,when the vaccine of H5 subtype of highly pathogenic AI was used for immunization compulsively.Since 2013,the H7N9 subtype of AI has brought great harm to the development of poultry industry and human health,in particular,the H7N9 subtype of AIV mutated into highly pathogenic at the end of 2016,which caused huge losses on farms in China.The development and application of "H5 + H7 bivalent inactivated vaccine" has played an important role in preventing the occurrence and epidemic of H5 and H7 subtypes of AI in China.However,due to the improper selection of vaccines and the unreasonable formulation of immunization procedures,AI still occurs from time to time.In order to solve these problems,based on the epidemiological investigation of AI,the bivalent inactivated vaccine of recombinant AI(H5+ H7)and the AI recombinant Newcastle disease virus bivalent vaccine,Live(r L-H5 Strain),were selected as the candidate vaccines.In this paper,the evaluation of immune effect in farm,optimization of immune procedure and application of AI vaccine were studied.The main research contents and results are as follows:(1)In the study of the aetiological investigation of AI,for the period 2015-2017,chicken throat and cloacal cotton swabs as well as tissues and organs suspected of AI,collected from 10 farms,self-employed farmers and some live poultry markets in the three northeastern provinces were tested for pathogens.For H5 subtype AI,2216 samples were all negative;for H7 subtype AI,2 samples were positive in 3041 samples;for H9 subtype AI,12 samples were positive in 2661 samples.By sequencing and analyzing the positive samples of two H7 subtype AIV strains,it was found that in the two H7 subtype AIV strains,the HA gene had the cleavage sites of “-ARTAR*G-”and the potential glycosylation sites of “NST/NVT/NSS/NGS”;There were no mutations at the sites associated with Oseltamivir phosphate resistance in the NA gene;and there were no mutations at the sites associated with the virulence and resistance in the internal genes,such as PB2,NS,M and PA gene.These characteristics are consistent with highly pathogenic AIV.(2)The investigation of AI vaccine immunization program and surveillance of antibody levels in farm showed that,in the 10 farms monitored in this study,only the inactivated vaccine was used,and 4 times of inactivated vaccine were given before laying,which were about 15,45,70 and 110 days respectively.And inactivated vaccine was vaccinated every 3 months during laying period.Surveillance of antibody levels showed that,the eligible rates of H5,H7 and H9 subtype AI antibodies were 90.31%-97.72%,90.97%-96.48% and 81.51%-97.88%,respectively.It meets the immunization qualifification rate required by Animal Disease Imumune Surveillance Program.According to the surveillance data of AI in China,various subtypes of AI still break out sporadically under the condition of high immunization frequency and high qualified rate of antibody,which indicates that there are still loopholes in the field production.(3)Comparative analysis of immune evaluation indexes of AI.Based on the surveillance data of AI immune antibody in 10 farms,the relationship among antibody level,dispersion and boundary slip(Q)of AI immune status in chickens were analyzed.According to the National AI Standard,the test result of immune antibody is qualified when it is more than 4log2,the qualified rate of population antibody is qualified when it is more than 70%,and the dispersion is qualified when it is less than 20%.These two indexes can reflect the immune level of chickens to some extent,despite there are some errors,the boundary slip(Q)is more meaningful to guide farm production.When Q ? 50%,the health status of birds is relatively stable.When Q ? 100%,not only the health status of chickens is stable,but also has little influence on egg production,and even if the egg production drops due to some factor,its recovery is also faster.When Q < 50%,the health status of poultry population was very unstable,which suggested that the corresponding vaccine should be immunized in time.The evaluation index of the difference rate can reflect the immune level and the overall health state of the chicken population,which is of great significance to know the immune status and to decide the immune date in time.(4)Optimization of immune procedure for AI vaccine.The optimization of immune procedure mainly includes the optimization of immune times,the optimization of first immune day,and the optimization of combined application of vaccines.The results showed that,the best immunization time of the inactivated vaccine was 3 times before laying;for the first immune day,there was no significant difference among 7-,10-and 14-day-old for AI recombinant Newcastle disease virus bivalent vaccine,Live(r L-H5 Strain),however,consideration of the immune procedure of Newcastle Disease,the best immune age of combined live vaccine was 7-day-old,the optimal first immunization age of the recombinant AI(H5 + H7)bivalent inactivated vaccine was 10-day-old;for the combined application of vaccine,the combined application of the two vaccines is more effective,especially the rational use of AI recombinant Newcastle disease virus bivalent vaccine,Live(r L-H5 Strain),during laying period can reduce the immune side effects and reduce the cost of breeding.(5)The results of clinical application of optimized immune procedure of AI vaccine showed that high antibody level could be obtained after 3 times of immunization before laying of hens.The qualified rate of antibody is 100%,the dispersion of antibody is less than 20%,and the Q value is more than or equal to 100%,the chickens are in stable health and good production performance.The side effect of AI recombinant Newcastle disease virus bivalent vaccine,Live(r L-H5 Strain),on egg production rate is less than that of inactivated vaccine,so it is recommended to use recombinant live vaccine for immunization at egg production peak.In a word,through the investigationof epidemiological,immune procedure and antibody level monitoring of AI,we found the problems in the use of vaccines in farm.Then,the immune procedure of AI vaccine was optimized by the comparative analysis of immune evaluation indexes,the detection of vaccine quality and the evaluation of vaccine immune effect in farm.The optimized immunization program was applied to the farm and good results were obtained.These results will provide scientific guidance for the establishment of scientific and reasonable immunization procedure of live vaccine and inactivated AI vaccine in the farm,and for ensuring the immune effect of AI vaccine in the farm. |
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