Molecular Epidemiological Investigation And Pathogenicity Of Subgroup J Avian Leukosis In Part Local Breeders And Imported Broiler Breeders

Subgroup J avian leukosis is a tumorous diseases caused by subgroup J avian leukosis virus subgroup(ALV-J)and characterized by excessive proliferation of certain cell components in Avian hematopoietic tissues.ALV-J was first detected in broiler chickens in China since 1999,followed by scattered reports of infection of layer and local chickens,resulting in huge economic losses to Chinese breeding industry.After 2013,although the incidence of avian leukosis in laying hens in China was significantly reduced,it still caused serious harm in local breeders and imported broiler breeders.Objective: The study investigated the molecular epidemiology and pathogenicity of ALV-J in part local breeders and imported broiler breeders in china,and laid a foundation for mastering its epidemic trend,molecular characteristics and pathogenicity.Methods: Our study isolated and identified some isolates based on the methods of virus isolation,ELISA antigen detection and multiple PCR.The full genome sequence were amplified and sequenced by PCR.A variety of sequence analysis softwares were used to compare the whole genome sequence of isolates with that of reference strains.Further,virus suspension(local breeders and imported broiler breeders ALV-J isolates)was injected into the intraperitoneal per one 1-day-old SPF chicken Since 3,5,7,9,11,13,17,21,24,28,30,32 weeks after infection,samples of cloacal swabs,anticoagulant and non-anticoagulant blood were collected to study the virus-infected stutus such as virus shedding,viremia,and specific antibody to ALV-J and clinical symptoms and pathological changes were also observed.Results:(1)Our study collected the unknown pathogen from 260 samples collecting from 10 farms of 5 provinces in China and isolated 18 ALV-J isolates During 2013~2018.Sequence characteristics as follows: the full genome sequence analysis indicated that variation is mainly focused on gp85,3 ` UTR,3 ` LTR gene,etc.Gp85 amino acid analysis showed that a few isolates(3/18)were closely related to ALV-J broiler strains.Some isolates(3/18)were closely related to layer strains.However,most isolates(9/18)were closely related to local breeders and formed independent branches.rTM of 3 ` UTR of most local breeders ALV-J is missed,kept the complete E element;U3 region appeared 9 bp base substitution.Among the 18 isolates,the homology between G266 and all the reference strains was less than 90 %.The pathogenicity study showed that detoxification(15%)began on the 6th day,after which the detoxification rate fluctuated greatly,and viremia maintained a high level after the 7th W.antibody production was not detected during the whole process.(2)Since 2018,this study had collected 55 samples of 6 batches which suspected avian leukosis samples from imported broiler breeders farms in liaoning,shandong and other places,from which 8 ALV-J isolates were isolated,sequenced and analyzed.The full gene sequence characteristics were as follows: gp85 amino acids of 8 ALV-J isolates showed the homology of less than 92.5 % with other ALV-J reference strains,while its showed high identity with the GD14J2 isolate from parental broiler breeders in 2014 and belonged to same branch.The 3’UTR region was continuously missing 210 bp in the rTM and DR-1 region and 125 bp in the E element,which was consistent with GD14J2.U3 region in 3’LTR had higher homology with GD14J2 strain(94.3 %~96.3 %).Pathogenicity study found that detoxification began on the 10 th day after infection,and viremia was detected in the 2nd W and the positive rate was 100%.After that,it changed continuously at different times and fluctuated greatly.The whole process always had antibodies and fluctuated at low levels.Conclusion:(1)18 ALV-J isolates were isolated and identified from part local breeders.Most isolates had evolved a separate genetic branch in gp85,U3 region.The E element in 3 ` UTR region was conservative,and its found nine unique base substitution in U3 region.After G266 isolate was infection with SPF chicken,there is no induction of antibodies,but there is persistent viremia,intermittent detoxification.(2)Since 2018,imported broiler breeders emerged suspected cases of avian leukosis in the china,we have determined that the pathogen of the outbreak was ALV-J in the previous survey,Sequence analysis suggested that the ALV-J isolates may be from the same source as the GD14J2 isolate,both of which were imported from foreign white feather progenitor broiler.Pathogenicity studies found that the infected SPF chickens induced low levels of antibodies,intermittent viremia and detoxification.The above study provides useful data for the analysis of the variation trend and source of ALV-J in local breeders and imported broiler breeders.