Avian Leukosis Virus Subgroup J in Layer Chickens, China

To the Editor: In recent years, cases of avian leukosis virus subgroup J (ALV-J) infection and tumors in commercial layer chickens and breeders of egg-type chickens have been emerging in the People's Republic of China.ALV-J was fi rst isolated from meattype chickens with myeloid leukosis in 1988.Although egg-type chickens have been experimentally infected with ALV-J to induce tumors (1), fi eld cases of ALV-J infection and tumors in commercial layer chickens were not found worldwide until 2004 (2).ALV-J has recently been found to have induced various tumors and caused production problems in commercial layer fl ocks and local chicken breeds in China (2,3).Many fi eld cases of ALV-J infection and tumors have occurred in 15-to 29-week-old eggtype chickens in several provinces.Affected fl ocks had dramatically reduced egg production and hemorrhage in the skin surrounding the phalanges and feather follicles.Some birds had graywhite nodules in the liver, spleen, or kidneys, and liver and spleen were enlarged up to several times their normal size.Morbidity rates for some fl ocks reached 60%, and mortality rates for some fl ocks were >20%.Clinical samples from livers, spleens, whole blood, and tumors were collected from chickens in different provinces and sent for laboratory diagnosis.Results showed that the predominant virus in the samples was ALV-J.During 2007-2009, we conducted an epidemiologic investigation of ALV in layer fl ocks in China.All virus isolation was performed in DF-1 cells.Briefl y, 233 clinical samples were collected from 44 layer fl ocks in different provinces and used to inoculate subconfl uent cell cultures containing Dulbecco modifi ed essential medium