| Newcastle disease（ND）is a highly contagious disease caused by Newcastle disease virus（NDV）,usually hosted by chickens,turkeys and a variety of birds.Guangdong province is located in the land border of China.The climate is warm and humid.Water area is vast and waterfowl industry is developed,so it is the high-frequency area of ND.Diseases caused by NDV have seriously threatened the development of the breeding industry.Therefore,during the period from August 2016 to December 2018,our research group carried out the epidemiological monitoring of NDV in Guangdong province.In recent years,NDV detection methods are diverse and disorderly,but the lack of a unified standard.In order to improve the detection method and efficiency of NDV,in this study,we evaluated 5 pairs of published qRT-PCR primers for NDV detection and screened out a pair of suitable primers,which were applied in NDV detection.During the monitoring process,we have isolated a total of 4 NDV strains.One of them is a genotype Ⅻ NDV which was isolated from the goose in live poultry market of Guangdong,named Goose/CH/GD/E115/2017（E115）.Up to now,only 6 strains genotype Ⅻ NDV were isolated in China and correlation research is rarely.In this study,the whole gene of this isolate was sequenced and analyzed.We analyzed the genetic evolution of the F genome,researched its Mean death time（MDT）and Intracerebral pathogenicity index（ICPI）,chose SPF chickens and non-immune geese as experimental animals to evaluate the pathogenicity and transmission in the intraspecific and interspecific,evaluated the protective effect of existing commercial vaccines on the market and researched its antigenic variation.During this study,we strive to have a more comprehensive understanding of this genotype of NDV.During the test,We performed whole genome sequencing and genetic evolution analysis of E115 strain.The whole genome sequencing results showed that the full-length gene of E115 strain was 15 192nt,with the substitution of N240S,and T496I in F protein.It locates at the same branch as the other six genotype Ⅻ NDV strains which were isolated in China from 2010～2013,belongs to the genetic Ⅻa subtype,but is different branch compared with Peru Ⅻb subtype and Vietnam Ⅻd subtype.The amino acid sequence of the F protein cleavage site is 112RRQKRF117,which meets the criteria for virulent toxicity.In order to understand the pathogenicity of E115 strain to SPF chickens and non-immune geese and the ability of intraspecific and interspecific transmission in these two animals.The MDT of E115 strain was 57.4 h and ICPI was 1.67 which was determined to be virulent toxicity.However,its pathogenicity and intraspecific and interspecific transmission test on SPF chickens showed that E115 virus strain can cause obvious clinical symptoms in infected chickens,which is characterized by depression,loss of appetite,neck twisting,lameness,and even paralysis,but no death.High virus titers can be detected in many organs such as liver,lung,and kidney.And detoxification can be detected in oropharynx and cloaca,the highest level of detoxification is achieved at 5 dpi.In addition,detoxification was also detected in oropharynx and cloacae of 3 cohabited chickens and 3 non-immunized geese at the age of 2 weeks in the same group,demonstrating that the virus could be transmitted in intraspecific through chickens and transmitted in interspecific to geese.The pathogenicity and intraspecific and interspecific transmission test of non-immune goose showed that infected geese could detoxification through oropharynx and cloaca,and the detoxification reached a peak at 5～7 dpi,Virus replication could also be detected in their liver,lungs,kidneys and other organs.Three geese and three chickens cohabited together were able to detect viral titers in the mouth and cloaca at 5～7 dpi.During the experimental period,there were no clinical symptoms and death in th e infected geese and chickens cohabited together.In the evaluation test of the protection effects of 2 commercial vaccines against E115 strain.By using LaSota inactivated vaccine and A-Ⅶinactivated vaccine to do immune protection experiments,the results showed that the detoxification can be detected in oropharyngeal swabs and cloacal swabs of infected chickens in the LaSota strain vaccine group during 3 to 5 dpi.And in the A-VII strain vaccine group,detoxification was detected in oropharyngeal swabs and cloaca swabs in 3 dpi in infected chickens.In the two experimental groups,the chickens in the cohabitation group were also able to detect detoxification throughout the experimental period.Both vaccines provide the chicken with a certain immunoprotective effect,but cannot prevent the spread of the E115 strain among them.In addition,the analysis results of the antigenic variation coefficient of E115 virus strain showed that the R-value between E115 strain and LaSota was 0.7783,and the R-value between E115 strain and mGM was 0.8133,which proved that the antigenic difference between E115 and LaSota and mGM strains was not significant.Hence,they could be determined to be the same serotype. |
