Phylogenetic analysis of subgroup J avian leucosis virus from broiler and native chickens in Taiwan during 2000-2002.

Subgroup J avian leucosis virus (ALV-J) causes great economic losses in the poultry industry. One in 3 grandparent farms was closed due to ALV-J infection in 1998 in Taiwan. The remaining 2 farms were forced to import breeding chicks from different breeding companies afterwards. We report on the ALV-J infection status among these breeders, their progeny and Taiwan native chickens during 2000-2002. The weekly mortality for the male line among the infected breeders was higher than that for the female line. Sixty-three percent (5/8) of the broiler flocks were infected with ALV-J. The surface (SU) portion of the env gene from the ALV-J field isolates was cloned and sequenced. The phylogenetic results show that all of the isolates fell into 2 clusters. Unexpectedly, the isolates from the same breeds fell into different clusters, with a cluster including isolates from different breeding companies. ALV-Js from native chickens crossbred with imported chickens were placed into the same clusters as those from the imported breeds. The high similarities observed in different ALV-J isolates suggest that different ALV-Js were mixed in the pedigree generations in different breeding lines.