| Avian leukosis(AL)is a type of neoplastic disease with multiple types caused by a group of viruses generally named the avian leukosis virus(ALV),which belongs to the Retrovididae.It has been resulting in huge economic loss to poultry industry.In this study,4 flocks of commercial layer chickens,originated from the same parent-stock company,were epidemiologically investigated and detected continually to study the states of ALV infection,the epidemiological characteristics and the main performance of flocks,isolation and identification of the virus and its genetic variation of viral gp85 gene,for the purpose to provide the basis data for the prevention and control of AL in layers.Birds in flocks A and C began to show obvious clinical symptoms at 10-week-old with significant tumors were found in the visceral organs of the diseased birds at the early stage of the diseases,and suspect myeloma was also found in the sternum of the diseased birds in flock A.The PCR detection results of the suspect tumor tissues showed that flock A was ALV+,MDV+ and REV-and flock C was MDV+,REV+ and ALV-.At the later stages of the diseases,the results of virus isolation and identification of the 26-week-old diseased birds showed that flocks A was MDV-,REV-and ALV+,and group C was MDV-,REV-and ALV-.At 5.8 weeks of age,eggs and blood samples of the birds from the four flocks were collected to detect the ALV-p27 antigen and to isolate ALV by cultivating in DF-1 cells,respectively.The results show that the p27 antigen positive rates of flocks A,B,C and D were 14.29%(15/105),10.92%(13/119),0%(0/104)and 0%(0/104),respectively.The positive rates of ALV isolation of the serum samples of flocks A,B,C and D were 9.78%(9/92),5.43%(5/92),0%(0/92)and 1.09%(1/92),respectively.On the laying performance,the housed hens’ laying rates of flocks A,B,C and D were 76.05%,84.94%,78.29%and 79.23%,respectively,in the stage of 19-72 weeks.Flocks A was significantly lower than that of flock B in the birds with the pink shell eggs,and it was not significantly different between the two groups of birds with the brown shell eggs(flocks C and D).In death and eliminate,the mortality rates of four.flocks were 37.51%,3.12%,.31.78%and 1.18%,respectively,in the stage of 0-18 weeks before laying,and were 18.06%,4.69%,9.58%and 9.55%,respectively,in the laying stage of 19-72 weeks.The mortality rate of flock A was significantly higher than others,while the high mortality rate of flock C was mainly in the incidence stage.The birds with clinical disease were necropsied and the suspect tumor samples were inoculated onto DF-1 cell cultures for virus isolation.An ALV-J strain named GX201507 was isolated by detections of the ELISA and PCR of the cultures.The glycoprotein gene gp85 of the isolate was amplified,sequenced and analyzed.It was found that its gp85 gene was 924 nucleotides in length and encoded 308 amino acids(aa).There were 12 aa-site mutations in the full length of gp85 protein,and the site-mutation S182G,A268V and L289H were strain-specific.The analysis of phylogenetic tree showed that the genetic relationship between GX201507 and the subgroup A,B,E reference strains SDAU09C3,SDAU09E3,SD0501 was farther and clustered in different branches,while the genetic relationship between GX201507 and other ALV-J reference strains GX14ZS14 and GX14FF01,originated from birds of Guangxi local breeds,reference strains FJ201308 and GL09DP01,originated from China layer chickens,and ALV-J prototype strain HPRS103 were closer,and clustered in the same branch.The analysis of gp85 homology showed that the sequence similarity between GX201507 and the subgroup A,B,E reference strains SDAU09C3,SDAU09E3 and SD0501 was low by 43.7%,44.3%and 43.5%,respectively,while those between GX201507 and other reference strains of subgroup J were 87.8%-98.4%,were 87.8%-98.4%between with 4 ALV-J isolates from Guangxi local breed chickens,were 88.7%-98.1%between with 5 ALV-J reference strains of China layer chickens,and were 89.6%-92.2%between with 5 ALV-J reference strains from white-feather broilers.And the highest similarity was 98.4%between with.a Guangxi reference strain GX14FF01,while that between with the prototype strain HPRS103 was 95.5%。The investigation showed that birds of 3 flocks were infected by ALV in the 4 flocks brooded at the same day from the same parent-stock company,and with only one flock’s birds experienced obvious clinical diseases with visceral organ tumors and sternal myeloma and there was a mixed infection of ALV and MDV found in the early stage of the disease.The laying performance of the flock that had suffered from avian leukosis was significantly lower than that of other normal flocks of the same breed,and the mortality rate was higher than others during the whole feeding period.An ALV-J strain was isolated from the clinical diseased birds and the isolate was higher similarity on gp85 gene with other ALV-J isolates derived from birds of China layers and Guangxi local breeds than that of isolates derived from the white feather broilers. |
PDF Full Text Request