Tilapia lake virus (TiLV) is an emerging pathogen in aquaculture, reportedly affecting farmed tilapia in 16 countries across multiple continents. Following an early warning in 2017 that TiLV might be widespread, we executed a surveillance programme on tilapia grow‐out farms and hatcheries from 10 districts of Bangladesh in 2017 and 2019. Among farms experiencing unusual mortality, eight out of 11 farms tested positive for TiLV in 2017, and two out of seven tested positive in 2019. Investigation of asymptomatic broodstock collected from 16 tilapia hatcheries revealed that six hatcheries tested positive for TiLV. Representative samples subjected to histopathology confirmed pathognomonic lesions of syncytial hepatitis. We recovered three complete genomes of TiLV from infected fish, one from 2017 and two from 2019. Phylogenetic analyses based on both the concatenated coding sequences of 10 segments and only segment 1 consistently revealed that Bangladeshi TiLV isolates formed a unique cluster within Thai clade, suggesting a close genetic relation. In summary, this study revealed the circulation of TiLV in 10 farms and six hatcheries located in eight districts of Bangladesh. We recommend continuing TiLV‐targeted surveillance efforts to identify contaminated sources to minimize the countrywide spread and severity of TiLV infection.

中文翻译：

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对罗非鱼湖病毒（TiLV）进行的为期两年的监测表明，罗非鱼湖病毒在孟加拉国多个地区的罗非鱼农场和孵化场中广泛传播。

罗非鱼湖病毒（TiLV）是水产养殖中的一种新兴病原体，据报道影响了多大洲16个国家的养殖罗非鱼。在2017年发出TiLV可能会广泛传播的预警之后，我们在2017年和2019年对孟加拉国10个地区的罗非鱼成长期养殖场和孵化场实施了监视计划。在死亡率异常的养殖场中，有11个养殖场中有8个的TiLV检测呈阳性在2017年，有七分之二在2019年呈阳性。对从16个罗非鱼孵化场收集的无症状亲鱼进行的调查显示，有六个孵化场的TiLV呈阳性。接受组织病理学检查的代表性样本证实了合胞性肝炎的病理性病变。我们从受感染的鱼类中回收了TiLV的三个完整基因组，一个来自2017年，另一个来自2019年。基于10个片段和仅1个片段的级联编码序列的系统进化分析一致显示孟加拉国TiLV分离物在泰国进化枝中形成了独特的簇，表明密切的遗传关系。总而言之，这项研究揭示了TiLV在孟加拉国八个地区的10个农场和六个孵化场的流通。我们建议继续以TiLV为目标的监视工作，以识别污染源，以最大程度地减少TiLV在全国的传播和严重程度。