Israeli Veterinary Services, Bet Dagan, Israel.
Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Transbound Emerg Dis. 2021 Nov;68(6):3025-3033. doi: 10.1111/tbed.13955. Epub 2020 Dec 30.
Tilapia lake virus (TiLV) is an emerging viral disease that affects several tilapia species in different countries since 2014. In 2017-2018, 129 samples were collected from 14 tilapia farms in Israel. Ninety samples represented mortality events (ME), and 39 were used as control samples (CS). RT-qPCR was performed on 89 and 39 duplicate brain and liver tissue samples from ME samples and CS, respectively. TiLV was diagnosed in 37 (41.6%) ME, while only two of the CS samples (5%) were positive for TiLV (OR = 13.2, 95% CI = 3.0-58.1). Additional RT-PCR was performed on positive samples, and amplified products were sequenced. Maximum likelihood phylogenetic analysis of segment-3 revealed three distinct clades: the first clade (A) includes 25 sequences of TiLV, detected previously in Israel (2011), Ecuador (2012), Egypt (2015), Thailand (2015-2019), India (2017), Peru (2018) and USA (2018-2019) and 11 sequences of TiLV from the current study (2017-2018); the second clade (B) includes only four sequences from Thailand (2018) and Bangladesh (2017 and 2019); and a third clade (C) which includes a single sequence from Bangladesh (2019). Out of the 39 sequences included in clade A, 14 closely related sequences of TiLV from the current study (2018) formed a distinctive sub-clade (IL-2018). Mann-Whitney U test showed differences in the distribution of survival rates between Israeli sequences (from 2011, 2017 and 2018) of clade A (p = 0.004) and Israeli sequences (from 2018 solely) of sub-clade IL-2018. The average survival rates of clade A and sub-clade IL-2018 were 58.1% (SD = 21.5) and 31.2% (SD = 25.6), respectively. This is one of only few field studies which show direct association of TiLV with mortality events in tilapia farms. The decrease in survival rate in the newly evolved clade might raise concern regarding virus evolution towards increased virulence, which should be further explored.
罗非鱼湖病毒（TiLV）是一种新兴的病毒性疾病，自 2014 年以来已影响到多个国家的多个罗非鱼品种。2017-2018 年，从以色列的 14 个罗非鱼养殖场采集了 129 个样本。90 个样本代表了死亡率事件（ME），39 个样本作为对照样本（CS）。对 ME 样本和 CS 的 89 个和 39 个脑组织和肝脏组织的重复样本进行了 RT-qPCR。在 37 个（41.6%）ME 中诊断出 TiLV，而 CS 样本中只有 2 个（5%）呈 TiLV 阳性（OR=13.2，95%CI=3.0-58.1）。对阳性样本进行了额外的 RT-PCR，扩增产物进行了测序。对第 3 节的最大似然系统发育分析表明存在三个不同的分支：第一个分支（A）包括 25 个 TiLV 序列，之前在以色列（2011 年）、厄瓜多尔（2012 年）、埃及（2015 年）、泰国（2015-2019 年）、印度（2017 年）、秘鲁（2018 年）和美国（2018-2019 年）检测到，以及来自当前研究（2017-2018 年）的 11 个 TiLV 序列；第二个分支（B）仅包括来自泰国（2018 年）和孟加拉国（2017 年和 2019 年）的四个序列；第三个分支（C）包括来自孟加拉国（2019 年）的单个序列。在 A 分支中包含的 39 个序列中，来自当前研究（2018 年）的 14 个密切相关的 TiLV 序列形成了一个独特的亚分支（IL-2018）。Mann-Whitney U 检验显示，A 分支的以色列序列（来自 2011 年、2017 年和 2018 年）和以色列亚分支 IL-2018 序列（仅来自 2018 年）的存活率分布存在差异（p=0.004）。A 分支和亚分支 IL-2018 的平均存活率分别为 58.1%（SD=21.5）和 31.2%（SD=25.6）。这是为数不多的几项实地研究之一，直接表明 TiLV 与罗非鱼养殖场的死亡率事件有关。新进化分支中存活率的下降可能引起对病毒向更高毒力进化的关注，这需要进一步探讨。
