台灣家禽白血病J亞群病毒的演化及不同亞群共同感染之分析

Abstract

家禽白血病病毒（Avian Leukosis Virus, ALV）屬於反轉錄病毒科（family Retroviridae），可引發淋巴球性白血病與骨髓球性白血病，雞隻一旦感染，常伴隨嚴重免疫抑制、生產性能下降、腫瘤生成及高死亡率，對全球家禽產業造成重大損失。根據病毒封套蛋白（envelope, env）序列差異，ALV可分為11個亞群（A-K），ALV-A與ALV-J亞群病毒最常見於雞場。ALV依傳播途徑可分為外源性與內源性，兩者間在雞隻體內或雞場環境中可能發生重組，增加了診斷與根除的難度。近年新興的ALV-K被認為可能為外源性與內源性病毒重組之產物，其致病性與其他亞群間的交互作用目前尚未釐清，亦缺乏在台灣地區的流行病學研究。本研究針對近年台灣家禽場所分離到之ALV-A、ALV-J及ALV-K進行親緣關係分析，同時利用RCAS（Replication Competent ALV LTR with a Splice acceptor）載體系統構築帶有台灣ALV-J封套蛋白之重組病毒，進一步探討不同亞群的交互作用。RCAS為禽類反轉錄病毒載體，可攜帶ALV env基因並搭載EGFP或mCherry螢光標記，適用於追蹤無細胞病變效應之ALV感染路徑。本研究比較RCAS病毒於多種永生化細胞株、雞初代細胞及三維（3D）類器官模型中的感染表現，以模擬不同條件下之病毒傳播與交互作用。統計2023至2025年間的家禽腫瘤病例，ALV陽性樣本中以ALV-J最常見，且ALV-J與ALV-K共同感染的現象最頻繁。進一步分析序列發現台灣ALV-J病毒株在近20年間持續產生變異，而ALV-K則相對穩定。透過RCAS病毒感染實驗，發現ALV-A與ALV-J在細胞內呈現不同的傳播模式。此外當與ALV-K共同感染時，ALV-A的感染受到抑制，而ALV-J的感染則顯著增強，顯示不同亞群間存在不一樣的交互作用。我們進一步比較不同支系之ALV-J病毒於單獨感染以及與ALV-K共同感染之差異，結果呈現其感染能力與在共同感染下的反應亦有所不同。本研究闡明台灣ALV之演化趨勢與亞群間的交互作用，並透過RCAS系統提供可量化且可追蹤的ALV感染模型，為後續探討其致病機轉與疫病控制策略奠定基礎。

Avian Leukosis Virus（ALV）, classified into Retroviridae family, is known to induce lymphoid leukosis and myeloid leukosis. Infected chickens often exhibit severe immunosuppression, reduced production performance, tumor formation, and high mortality rates, resulting in significant economic losses for the global poultry industry. Based on the envelope glycoprotein（env）, ALV is classified into 11 subgroups（A-K）, among which ALV-A and ALV-J are the most common subgroup infections in poultry farms. In addition, ALV can be further categorized as exogenous or endogenous depending on the transmission route. Recombination between exogenous and endogenous ALV is frequently observed in poultry farms, which further complicates pathogen detection and eradication. Recently, a novel subgroup, ALV-K, has been identified and is hypothesized to be a recombinant between exogenous and endogenous ALVs. Its pathogenicity and interactions with other ALV subgroups remain poorly understood, and its epidemiological status in Taiwan is largely uncharacterized. In this study, phylogenetic analyses were performed on ALV-A, ALV-J, and ALV-K isolates collected from Taiwanese poultry farms in recent years. To further investigate inter-subgroup interactions, we constructed recombinant viruses using the RCAS system, incorporating envelope proteins from field strains of ALV-J in Taiwan. RCAS（Replication Competent ALV LTR with a Splice acceptor）, an avian retroviral vector, was engineered to carry ALV env genes tagged with EGFP or mCherry, allowing visualization of viral spread in the absence of cytopathic effects. We evaluated RCAS viral infection profiles in multiple immortalized cell lines, primary chicken cells, and three-dimensional（3D）models to simulate viral transmission and interaction under various conditions. Analysis of tumor cases in poultry from 2023 to 2025 revealed that ALV-J was the most frequently detected subgroup, with ALV-J/ALV-K coinfections being particularly common. Sequence analysis showed ongoing genetic variation in Taiwanese ALV-J strains over the past two decades, while ALV-K strains remained relatively stable. Functional assays using RCAS viruses revealed distinct transmission patterns for ALV-A and ALV-J in cells. Notably, in coinfection experiments, ALV-K suppressed ALV-A infection but significantly enhanced ALV-J infectivity, indicating subtype-specific interactions. Further comparisons among ALV-J clades showed differences in infectivity and responses under coinfection with ALV-K. This study elucidates the evolutionary trends of ALVs in Taiwan and highlights the complex interplay among different ALV subgroups. By applying the RCAS system, we established a quantifiable and traceable model for studying ALV infections, providing a foundation for future research on viral pathogenesis and control strategies.