| Avian leukosis(AL)is an infectious avian tumor disease caused by avian leukosis virus(ALV).ALV belongs to the retrovirus family Retroviridae alpha retrovirus genus Retrovirus.The infection of ALV can cause chickens a variety of tumor diseases,but most infected birds have subclinical symptoms,such as growth retardation,immunosuppression or decreased egg production,that cause huge economic losses to the poultry industry.In recent years,the game fowl industry in Pingxiang,Guangxi has been growing and has become a big sector in poultry industry.However,the research on ALV infections in game fowls and the pathogens are considerable limited.Therefore,an epidemiological investigation of the ALV infections in game fowls and the whole genome sequencing and analysis of the representative isolates were performed in the study.The research and the result will enrich and supplement the AL epidemiological data of diferent breeds of poultry and will be helpful for the eradication for this unique breed of chicken in Guangxi.Due to the lack of effective therapeutic drugs and vaccines,the only measure available for the prevention and control of ALV infection is mainly through the eradication on the breeders.At present,ELISA is used to detect group-specific antigen P27 of ALV in the eradication program to eliminate the positive birds,but the method has the limitatios of complicated procecures,time-lasting,and requires special instruments.Therefore,the exploration for a method that is easy to operate,short in detection time,can be used to detect massive samples and maintaining considerable specificity and sensitivity of the detection has become an urgent need of the eradication work for the breeding company.The plasma samples and anal swabs from 61 breeding birds of game fowl from a biggest breeding company in Pingxiang were collected.The plasma samples were inoculated into DF-1 cells for the virus isolation and later the supernatant of the cell cultrues and the anal swab samples of the corresponding birds were detected for ALV-p27 by ELISA kit.The results showed that the positive rates of ALV-p27 antigen of the 61 cell-culture supernatants and the anal swab samples were 18%(11/61)and 44.3%(27/61),respectively.Three of the isolated strains GX18PX01,GX18PX02 and GX18PX03 were used to run the full-genome sequencing and analyzing.The results showed that the sequence similities of the gp85 gene of the isolates GX18PX01 and GX18PX02 with the ALV-B reference strains was 90.9%,belonged to the subgroup B,while the sequence simility of the gp85 gene of the isolate GX18PX03 with the ALV-A reference strains was 97.1%,belonged to the subgroup A.Interestingly,the U3 region sequences of the isolates GX18PX01,GX18PX02 and GX18PX03 had the highest homology with the ALV-J reference strains by 94.0%,94.4%and 96.3%respectively,while those with subgroups C,D,E and K were all less than 85%.Based on the findings,it was concluded that the isolates GX18PX01 and GX18PX02 were the recombinant ALV-B subgroup viruses with the U3 sequence of ALV-J,and isolate GX18PX03 was a recombinant ALV-A subgroup virus with the U3 sequence of ALV-J.The comparisons on the sensitivity and specificity of colloidal gold test strips and ELISA kits for detecting ALV-p27 antigen was performed.100 cell-culture supernatants and 100 meconium samples with known S/P values of ELISA detection were used to study in parallel by ELISA kit and colloidal gold test strips,including 10 samples with S/P value of 0.099 and below,30 samples with S/P value between 0.1 and 0.19,30 samples with S/P value between 0.2 and 0.29,20 samples with S/P value between 0.3 and 0.49,and 10 samples with S/P value at 0.5 and above.The results showed that detections on both the cell culture supernatant and the meconium the samples with S/P values of ?0.099 and?0.5(10 for each)run by the two methods,were consistent and the former was negative and the latter was positive.In the detections on cell culture supernatant,samples with S/P values in the range of 0.1-0.19,0.2-0.29,and 0.3-0.49,the consistency between the colloidal gold test strip and the ELISA kit was 60%,66.7%and 85%,respectively.In the detections on meconium,samples with S/P values in the range of 0.1-0.19,0.2-0.29,and 0.3-0.49,the consistency between the colloidal gold test strip and the ELISA kit was 46.7%,63.3%and 75%,respectively.And all the positive samples detected by the colloidal gold test strip were also positive detected by the ELISA kit.The results showed that even the sensitivity of the detection with the colloidal gold test strip was lower than that of ELISA kit,but it has the very good specific and the advantages of simple operation,shorter detection time and no requirement of special equipments.The results of this study demonstrated that there is a considerable degree of ALV infection in game fowls in Guangxi Pingxiang,there are different subgroups coexist in the same flock and the representative isolates are recombinant viruses.Although the sensitivity of colloidal gold test strips for detecting ALV-p27 antigen is lower,but it is more suitable for rapid detection for massive sample in the field. |
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