中文摘要：

蛋用型鸡虽在试验条件下可以感染ALV-J，但自然感染时很少引起发病。然而，近年来在中国蛋鸡群中ALV-J发病严重，本研究对2008年以来ALV-J蛋鸡分离株的3′非编码区（3′UTR）进行了系统的分析。结果表明，89.5%（17/19）的ALV-J蛋鸡分离株的3′UTR出现了205 bp的缺失，94.7%（16/17）ALV-J蛋鸡分离株保留了完整的E元件。84.2%（16/19）的ALV-J蛋鸡分离株的U3区序列与肉鸡分离株的相似性低于92.5%，所有转录调控元件高度保守。ALV-J蛋鸡分离株的E元件和U3区均出现了多个碱基的突变。这些结果表明，ALV-J蛋鸡分离株的E元件和U3区正在迅速的演化，明显不同于肉鸡分离株的序列特征。这些发现有助于更好地了解ALV-J引起蛋鸡群发病的致病机理。

英文摘要：

Avian leukosis virus subgroup J （ALV-J） was first isolated from meat-type chickens in 1988. No field cases of ALV-J infection and tumors in layer chickens were observed worldwide until 2004. However, layer flocks in China have experienced outbreaks of this virus in recent years. The molecular epidemiology of 3′UTR of ALV-J strains isolated from layer flocks was investigated. A total of 205 nucleotides were deleted from the 3′ untranslated region of 89.5% （17/19） of the ALV-J layer isolates. Approximately 94.7% （16/17） of the layer isolates contained a complete E element of 146-149 residues. The U3 sequences of 84.2% （16/19） of the ALV-J layer isolates displayed less than 92.5% sequence homology to the ALV-J broiler isolates, although the transcriptional regulatory elements that are typical of avian retroviruses were highly conserved. Several unique nucleotide substitutions in the U3 region and the E element of most of the ALV-J layer isolates were detected. These results suggested that the E element and U3 region in the ALV-J layer isolates have evolved rapidly and were significantly different from those of the ALV-J broiler isolates. These findings will contribute to a better understanding of the pathogenic mechanism of layer tumor diseases induced by ALV-J.