Eradication Of Avian Leukosis In Three-yellow Chickens And The Pathogenicity Study Of The ALV Isolates In Guangxi

Avian Leukosis(AL)is one of transmissible neoplastic diseases,mainly resulting in some kinds of hematopoietic cells hyperlasia,which is caused by avian leukosis virus(ALV)that belong to the family Retroviridae.Based on cross-neutralization,virus interference assays and host range,ALVs are divided into ten subgroups A-J,and a newly reported subgroup K isolated in 2012.ALV infection mainly resulted in tumor and emaciation,mal-development of chicken and the reduction of performance such as the decreases of egg production and their fertility,also the immune suppression and nonspecific resistance decline,and it causes the huge economic losses in poultry industry.Mixture infection of multi-subgroup ALVs has been recognized as a common condition in native chicken flocks in china in recent years that may result in increasing pathogenicity of infection and possible recombination.Since the lack of effective medicines and vaccine to treat and prevent ALV infection at present,so the strict eradication program is the only effective measure for the control of AL.Guangxi is one of the most abundant province of native chicken breeds and many excellent local breeds have been successful developing and creating great commercial value.Three-Yellow chicken in a Guangxi commercial breeding company DGGX4 that has been the biggest chick-produce company consisted of pure lines A,B and C,was chosen to carry out for the eradication practice in the study.The mainly measures of eradication included the detecting of each individuals and elimination of the positives and breeding with the negatives,applying the strict bio-security measures to prevent the contamination and vertical transmission of the eggs and offspring,eliminating the infection through the contamination of vaccines.After 8 generations’ eradication(from generation 0 to 7),the ALV-p27 antigen positive rates of the hens in lines A,B and C were significantly dropped from 44.36%,8.14%and 7.9%to 0.80%,0.91%and 0.94%,respectively;the positive rates of the cocks in lines A,B and C were significantly dropped from 45.36%,17.50%and 15.45%to 1.46%,2.64%and 1.64%.Positive rates of subgroup A/B antibody and subgroup J antibody were significantly dropped to 4.34%,2.17%,3.26%and 6.52%,5.43%,6.52%,respectively.The data showed the eradication program was effective and successful.The pathogenicity of the field isolated ALV-J mono-infection and mix-infection of multi-subgroup ALV including ALV-A,ALV-B and ALV-J(ALV-M)was carried out to day-old chicks of Three-Yellow birds through peritoneal injection.The results were showed that both the ALV-J and ALV-M infection were reproduced and the affected birds showed extreme emaciation and hypoplasia,comb paleness and the hemangioma found on toes,skin,liver,kidney and mucous membrane on intestine.Swollen and whitish tumor nodules were also found in liver and spleen,and the bulb-shape tumor was found in the kidney as the clinical cases.The body-weight gains of infected groups at 5-week-old and afterwards were very significantly lower than that of the uninfected group(P<0.01).The thymus/body weight rations of the infected groups were very significantly lower than that of the uninfected group(P<0.01)at 1,5and11 weeks of age,and the bursa/body weight rations of the infected groups were significantly higher than that of the uninfected group(P<0.05)at one-week-old,and spleen/body weight rations of the infected groups were very significantly higher than that of the uninfected group(P<0.01)at 11-week-old.And the antibody responses of the vaccination of NDV,AIV-H5 and-H9 in the infected groups were suppressed to some extent.Histological examination revealed that mass proliferation of lymphocytes and myeloblasts were observed in liver,kidney were mainly proliferated with myeloblasts that much acidophilic cytoplasm.Blood routine examination:the counts of WBC and LYM of the infected groups were significantly lower than those of the uninfected group(P<0.05)at 21-week-old,even through were not statistically different during one-week-old and 15-week-old(P>0.05).The CD4+/CD8+ rations were significantly lower in the infected groups than the uninfected group(P<0.01)at 11-week-old.These datas indicated that the infections of ALV-J and ALV-M can result in immunosuppression,and the ALV-M was more serious.