| Avian infectious bronchitis(IB)is an acute and highly contagious infectious disease caused by infectious bronchitis virus(IB V).The disease mainly causes respiratory system and urogenital system lesions,resulting in chicken death,slow weight gain of broilers,and decreased egg production of laying hens.IBV is prone to variation,and there are many serotypes and genotypes,and new serotypes and genotype strains continue to emerge.There are large antigenic differences between different strains.Therefore,the prevention and control of IBV by vaccine immunization still has the problem that it is impossible to cover all genotypes.The prevalence of IBV varies in different periods,different regions and different types of chickens.It is very important for the prevention and control of IBV and the development of vaccines to grasp the epidemic characteristics of IBV in time,especially to understand the changes of epidemic genotypes in time.In this study,the epidemic situation of IBV in some areas of China in the first half of 2021 was investigated.A total of 5730 throat and cloacal swab samples and environmental samples of chickens,ducks,geese,pigeons and quails were collected from 12 provinces such as Anhui,Fujian and Guangdong.The collected swabs were inoculated with chicken embryo virus isolation and RT-PCR detection was performed.The S1 gene of IBV was sequenced,and the genotype and genetic evolution of IBV were analyzed,which provided a scientific basis for mastering the overall infection rate and epidemic characteristics of IBV in poultry in China.The results showed that 916 IBV positive samples were detected in 5730 samples,and the total positive rate of individuals was 15.99%(916/5730).The positive rates of IBV individuals in 12 provinces were 2.50%-25.63%,respectively.The individual positive rate of IBV in chickens was 27.06%(889/3282),in ducks was 0.96%(14/1455),in geese was 1.40%(5/357),in pigeons was 0.84%(5/592),in quails was 0(0/5),and in environmental samples was 10.26%(4/39).The overall positive rate of field points in 12 provinces was 73.96%(71/96).Genetic evolution analysis showed that 545 of 916 strains of IBV belonged to 9 pedigrees:201 strains of GI-19(QX type)and 107 strains of GI-13(4/91 type),which were the two main prevalent pedigrees at present.In recent years,GI-19 is the most prevalent strain in poultry flocks in China,causing significant economic losses to the poultry industry.Therefore,in-depth study of GI-19 IBV is of great significance to prevent and control the occurrence and prevalence of IBV in China.In this study,the passage characteristics,pathogenicity to chicken embryo,EID50 and pathogenicity to chicken of 7 strains of GI-19 IBV were studied.The results showed that 7 IBV isolates could be passaged stably in chicken embryos.The isolated strain S1402 was pathogenic to chicken embryos,and the typical pathological changes were small embryo curling.The EID50 test results of the second to fifth generations were 103.12/0.1ml,10-5.24/0.1ml,10-5.83/0.1ml and 10-5.33/0.1ml,respectively.Then,the EID50 was determined again with the second generation after the passage of the swabs from the experimental animals challenged with the isolate S1402,and the detection result was 104.16/0.1ml.However,the isolate S1402 had no pathogenicity to chickens.The isolated strain C1452 had no pathogenicity to chicken embryos,but the incidence rate to chickens was 33.33%(5/15).The typical pathological change was the deposition of uric acid salt in the kidney of chickens.This study provides a scientific basis for the development of new vaccines and differential diagnostic reagents for IBV epidemic strains,and provides a reference for the comprehensive prevention and control of IBV.High-throughput sequencing technology(NGS)was used to perform genome-wide sequencing of the selected 6 strains of GI-19 IBV.Homology and phylogenetic tree analysis of the sequencing results with the reference strains of IBV in each pedigree and 10 open reading frame sequences were performed.The amino acid sequences of partial structural proteins of the 6 isolates were analyzed,including antigen prediction,transmembrane region prediction,potential glycosylation site prediction,potential phosphorylation site prediction and homologous recombination analysis.The results showed that the isolates S1402 and C1452 were different from the other four isolates,and the isolate S1402 showed homologous recombination in the lab region.The homology of the whole genes of the six isolates was 96.0%-100%;the homology with the reference sequence was 85.0%-96.7%.This study enriched the IBV data and provided technical support for the follow-up study of IBV. |
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