Abdullah Azila, Pazai Afzan Muntaziana Mohd, Ridzuan Mohd Syafiq Mohammad, Sudirwan Fahmi, Hashim Shahidan, Abas Adnan, Murni Munira, Roli Zuraidah, Ramly Rimatulhana, Firdaus-Nawi Mohd
National Fish Health Research Division (NaFisH), Fisheries Research Institute (FRI) Batu Maung, Department of Fisheries Malaysia,11960 Batu Maung, Penang, Malaysia.
Freshwater Aquaculture Fisheries Research Division, Fisheries Research Institute (FRI) Glami Lemi, Department of Fisheries Malaysia, 71650 Titi Jelebu, Negeri Sembilan, Malaysia.
Vet World. 2022 Apr;15(4):1097-1106. doi: 10.14202/vetworld.2022.1097-1106. Epub 2022 Apr 27.
One of the emerging viral diseases in freshwater fish is Tilapia lake virus (TiLV), which infects all stages of fish and results in mass mortalities. Previously, a TiLV case was detected in the wild environment in Malaysia that involved tilapia and tinfoil barb. Hence, this study aimed to determine the presence of TiLV in wild tilapia () as well as tinfoil barbs () at the similar lake after the initial outbreak in year 2017.
Both fish species were sampled from this lake at a month interval for two years and subjected to TiLV detection using reverse transcriptase-polymerase chain reaction and cell culture isolation. Concurrently, bacterial isolation and water quality measurements were performed to deduce their correlation with TiLV occurrence. Other wild fish species and mollusk were also occasionally sampled during the fish inventory activity at this lake. The fish's weight, length, and associated clinical signs were noted throughout the entire study period.
Mortality was not observed throughout the whole study period, and results indicated a moderate to high prevalence of TiLV infection in both tilapia and tinfoil barbs. There was no correlation between TiLV infection with the isolation rate of opportunistic bacteria such as ., and . in the study site. At the same time, the Pearson correlation test revealed a moderate negative correlation between the water pH with the presence of TiLV (R=-0.4472; p<0.05) and a moderate positive correlation between the water iron content with the monthly detection of . in wild tilapia. This is contrary to tinfoil barbs, where there was a moderate negative correlation between the water iron content with the monthly isolation of . (R=-0.5190; p<0.05). Furthermore, isolation of TiLV on cell culture-induced viral invasion was resulted in the cytopathic effects.
Our results suggest that the wild fish may harbor TiLV for an extended period following a massive die-off event in 2017 without any obvious clinical signs and mortality. The persistency of viruses in the wild may need continuous and effective control as well as prevention strategies.
罗非鱼湖病毒（TiLV）是淡水鱼中一种新出现的病毒性疾病，它可感染鱼类的各个阶段并导致大量死亡。此前，在马来西亚的野生环境中检测到一起涉及罗非鱼和锡箔 barb 的 TiLV 病例。因此，本研究旨在确定在 2017 年首次爆发后，同一湖泊中的野生罗非鱼（）以及锡箔 barb（）中是否存在 TiLV。
在两年时间里，每月从该湖泊采集这两种鱼类样本，采用逆转录 - 聚合酶链反应和细胞培养分离法进行 TiLV 检测。同时，进行细菌分离和水质测量，以推断它们与 TiLV 发生的相关性。在该湖泊的鱼类清查活动中，还偶尔对其他野生鱼类和软体动物进行采样。在整个研究期间记录鱼类的体重、长度及相关临床症状。
在整个研究期间未观察到死亡情况，结果表明罗非鱼和锡箔 barb 中 TiLV 感染的患病率为中度到高度。在研究地点，TiLV 感染与诸如.、和. 等机会性细菌的分离率之间没有相关性。同时，Pearson 相关性检验显示水的 pH 值与 TiLV 的存在呈中度负相关（R = -0.4472；p < 0.05），水的铁含量与野生罗非鱼中. 的月度检测呈中度正相关。这与锡箔 barb 相反，在锡箔 barb 中，水的铁含量与. 的月度分离呈中度负相关（R = -0.5190；p < 0.05）。此外，在细胞培养上分离 TiLV 诱导病毒入侵会产生细胞病变效应。
我们的结果表明，在 2017 年大规模死亡事件之后，野生鱼类可能长期携带 TiLV，且没有任何明显的临床症状和死亡情况。病毒在野外的持续性可能需要持续有效的控制以及预防策略。
