TILAPIA LAKE VIRUS: AN EMERGING PATHOGEN IN THAILAND

Tilapia is the most important freshwater fish in Thailand with annual production of 200,000 metric ton. During 2015-2016, we investigated the massive die-off of red and Nile tilapia due to an unknown cause in Thailand. The disease has been called tilapia one month mortality syndrome (TOMMS). The cumulative mortality rate is 20-90 percent with peak of mortality occurred during 2 weeks since the moribund fish have been observed. The clinical signs of disease fish include lethargy, skin hemorrhage and congestion, skin and fin erosion, pale discoloration, exophthalmos and abdominal swelling. Here, we used reverse transcriptase polymerase chain reaction (RT-PCR) and virus isolation to confirm the presence of recently discovered tilapia lake virus (TiLV) in diseased tilapia in Thailand. The virus infected permissive cell line with cytopathic effect (CPE) development in 3 to 5 days post inoculation. Transmissible electron micrographs of infected cell and fish tissues showed round enveloped virions of 60 to 80 nm with characteristics very similar to those of Orthomyxoviridae. Additionally, genome analysis indicated that Thai TiLV is closely related to Israel TiLV. This is the first report of TiLV in Thailand and in South East Asia. At present, TiLV has been reported in Israel, Ecuador, Colombia, Egypt and Thailand. The spread of this emerging virus highlights that it is a potential threat to tilapia aquaculture in Thailand, Asia, and worldwide.