| Avian leukosis virus(ALV)has been reported that caused great outbreak and epidemics in the world.Due to high pathogenicity,mortality and incidence of tumors has caused economic losses in poultry industry.ALV is expanded exponentially mainly by vertical transmission,the samples of hatching eggs and semen play an important role in the vertical transmission of the virus.ALV eradication has been carried out by detecting the plasma samples and egg albumen for the presence of ALV,and breeder cocks detection were ofen overlooked.The detection of ALV in plasma or cock semen for virus isolation in eradication breeder cocks is not clear.In addition,the ALV will result in decresing the body weight,egg production and more mortality after infection,causing great risks to the chicken flocks.However,it had an extortionate ALV infection rate in some Chinsese local chicken breeds,the high rate of ALV infection was reduced by variety methods and reduce the pathogenicity of chickens due to the vertical transmission.In this present study,chickens were inoculated with ALV-J via yolk sac in embryos to establish ALV vertical transmission model,and reverse transcriptase inhibitors(RTI)such as AZT were adminisatrated in infected chickens to evalvate the effect of RTIs in reducing the pathogenicity of ALV-J in chickens.1.Detection of ALV in plasma and semen in breeder cocks The samples of plasma and semen were collected from breeder cocks from two farms which had been implementing ALV erdadication program in China and inoculated to DF-1cells for isolating the virus and compare two different detection method to evaluate the ALV infection,and a few isolates were sequenced and analyzed.The results showed that 11 semon samples are positive,13 plasma samples are positive in total 400 samples from breeder cocks in layer farm,total of 8 samples were ALV positive in both plasma and semen.In another pheasant farm,there were 45 positive semon samples and 188 positive plasma samples weredetected in total 1800 samples from breeder cocks,while,the total of 16 samples were ALV positive in both plasma and semen.The results demonstrated that it can not effectively detected the ALV-positive breeder cocks by virus isolation from plasma or semen alone.ALV isolation should be performed using both plasma and semen samples at the same time to determine the ALV-positive chickens.Analysis of gp85 gene sequences of patial isolated virus from layer farms showed that the homology of the isolates was 99.0%-100%.The homology of these samples was 88.6% ~ 99.2% with subgroup A,which was significantly higher than that of B,E,F,J,K that were 83.2% ~ 83.7%,85.4% ~ 89.6%,83.0% ~ 83.9%,50.0% ~51.1% and 84.8% ~ 85.9% respectively.Phylogenetic analysis demonstrated that all samples were in same branch brach with subgroup A.2.Protective effects of reverse transcriptase inhibitors on SPF chickens infected with ALV Chicken embryos were inoculated with ALV-J strain NX0101 via yolk sac to establish ALV vertical transmission model.Chickens were hatched and divieded into two groups.Chickens were injected with 5mg Zidovudine(AZT)and 2mg Lamivudine(LAM)via intramuscularly last one week for treatment group.Chickens were injected physiological saline in same volume intramuscularly at the same time as control group.Chickens were hatched to evalvate the effect of RTIs in reducing the pathogenicity of ALV-J in chickens.The results showed that the body weight and antibody titers of NDV and AIV-H9 in untreatment chickens were significantly lower than treatment group with AZT and LAM,more significantly lower than the control group.However,NRTI treatment could not prevent ALV replication in chickens,indicating that the drugs could not replace the eradication program.The above data not only illustrated the phathology of ALV-J by vertical transmissionin for the chicken flocks,it also showed that NRTI such as AZT and LAM helps to reduce the risk of vertical transmission of ALV-J in chicken flocks. |
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