| Since its discovery in the late 1980's (Payne, et al. 1991) avian leukosis subgroup J (ALV-J) has been recognized as a major disease issue for the poultry industry worldwide. To better understand the pathogenesis, impact and variability of ALV-J, six isolates have been characterized. These isolates include Hc1, the North American prototype (Fadly and Smith, 1999) and five isolates that were obtained at the University of Delaware (UD) from broilers and broiler breeders of four common meat-type breeds.; The effects of ALV-J on broiler performance and vaccine response has been evaluated with three ALV-J isolates. Each isolate was assessed with both simulated horizontal and simulated vertical transmission. In each experiment, ALV-J inoculated chickens were reared in simulated commercial conditions. Production characteristics were evaluated and ALV viremia, homologous ALV-J neutralizing antibody and antibody to common avian viruses were monitored. Vaccine response was evaluated by challenge studies comparing the protection of ALV-J inoculates with that of the sham inoculated hatch-mates. These studies revealed a substantial adverse impact of ALV-J infection on broilers reared in commercial conditions. Results of the vaccine response study did revealed minor differences between ALV-J and sham inoculates in protection to challenge.; A study to assess the pathogenesis and transmission of ALV-J was performed in semi-isolation with one isolate. The role of age in disease development, viremia and homologous ALV-J neutralizing antibody was studied. Disease produced in the pathogenesis and transmission study was mild, in contrast to disease induced by the same isolate in the broiler studies. Results of the pathogenesis and transmission study also demonstrate that substantial horizontal transmission can occur.; In vitro characterization of the virus included antigenic characterization by cross-neutralization and analysis of selected regions of the genome of the UD isolates. The sequenced region included the 3 ' third of the genome, which contains the region that determines antigenic characteristics (the env gene), and regulatory elements. Both the antigenic characterization and sequence analysis demonstrate a high level of variability among the isolates studied. Sequence analysis reveals that the UD isolates vary in the ALV-J specific genome elements present, including regions which may effect growth. |
