Epidemiological Survey And Pathogenicity Study Of Avian Leucosis In Diseased Chicken Flocks In Shandong Province

Avian Leucosis (avian leucosis, AL) is one kind of transmissible neoplastic disease, mainly in hematopoietic cells hyperplasia, which is caused by alpha-retroviral retrovirus avian leucosis virus. The virus is divided into 10 subgroups A-J. ALV is epidemic in around the world by horizontal and vertical transmission, resulted in death, emaciation or maldevelopment of chicken, as well as nonspecific resistance decline and immune suppression, and it is to be the mainly disease threaten poultry industry. In order to alleviate its harm to the poultry industry and find a suitable antiviral therapy, research on its preventation and treatment is on an urgent schedule.1. Diseased Chicken Flocks of Shandong provinceThe ELISA test results indicated that p27 antigen and ALV antibody were positive in all stains of layer chickens including grandparent flock, the and antibody's positive rates of antigen p27, antibody ALV-A/B, ALV-J and REV were respectively 19.36%, 9.29%, 5.18%, 13.77%. There are also some chickens getting co-infection with ALV-A/B and ALV-J or with three viruses. The p27 antigen and antibody's positive rates of ALV-A/B rose gradually from grandparents to commodity of Hy-line. ALV infection existed in all stains of layer chickens in Shandong province, as well as co-infection with MDV, REV.The pathology diagnosis indicates that the tumors mainly involve myelocytoma (27/41), hemangioma (7/41), fibrosarcoma (2/41), leiomyosarcoma (2/41) and MD (5/41).The groups getting disease were mainly Commercial flock and parent flock, while there're also some Hy-line brown grandparent flocks getting disease. The results showed that ALV-J mainly caused hyperplasia proliferate of eosinocyte; even some serious samples'bone marrows were substituted by these cells. Therefore, research on marrow is significant on the study of ALV-J. In addition, ALV-J also caused apoptosis of lymphocytes and myelocytes proliferated in some visceralorgans.The PCR test result indicated that: Among the 41 samples, there're 33 samples positive for ALV-J (80.49 %), 22 samples positive for MDV (53.66%), and the co-infection rate was 43.9%. Among 17 virus stains isolated, the homologies of gp85 gene of ALV-J take up a rate ranged from 94.0% to100%. The 17 isolated virus stains shared 94.3% to 98.7% identity with HPRS-103, and shared low homology with other strains (84.4%-96.8%).The levels of Hailan egg chicken's WBC, LYM, PLT, MVP, and PCT are all lower than that of healthy control group and also distinguished significantly. While in another condition, there's little difference in RBC, MCH, and MCHC.These results indicated that ALV infection existed in all stains of layer chickens in Shandong province as well as co-infection with MDV, REV. Myelocytoma and hemangioma were the main clinical symptoms of sick chickens.2. Chinese native breed -Luhua chickenThe result indicates that the ALV-A/B antibody was positive for 13.24% at the age of 240 days and REV antibody was positive at the age of 120 days and also increased with aging, while ALV-J antibody was not detected .Positive rate of antigen P27 was ranged from 34.21% to 66.18%. The mortality was 32% from egg laying stage to the age of 240 day. Numerous similar nodular lesions and resembling tumors in one or more tissues were seen at necropsy tests and some sick chickens'sciatic nerve was edematous. Histopathology tests revealed large islands of lymphocytes in tissues containing tumors. Among 16 samples, 14 samples were detected positive for ALV-J (87.50 %), 13 samples for MDV (81.25%), 2 samples for REV (12.5%) and co-infection rate was 6.30%. All the findings observed in this case were considered to be related with mixed infection of MDV, REV and ALV, while mainly observed was disease of MD tumor.In the blood routine, the levels of Luhua chicken's LYM, RBC, MCH, and MCHC are all lower than that of healthy control group and also distinguished significantly. The levels of PLT, MVP, and PCT are also lower than the healthy control group and distinguished much more significantly. While in another condition, there's little difference in WBC.These results indicated that ALV infection existed in Shandong province and co-infection with MDV, REV were occured. Myelocytoma and hemangioma were the main clinical symptoms of sick chickens.