Title : Tilapia lake virus (TiLV) from Vietnam is genetically distantly related to TiLV strains from other countries
Tilapia lake virus (TiLV) is reported as a threat to tilapia aquaculture in 16 countries from four continents with outbreaks causing up to 90% mortality. Our study is the first one working on TiLV from Vietnam. We propagated successfully a TiLV isolate HB196-VN-2020 from a diseased tilapia sample using an E-11 cell line and evaluated its virulence in different weights of red hybrid tilapia and three serial 10-fold diluted viral titers. Small fish (4.5 ± 1.98 g) were proved to be more susceptible to TiLV infection at the viral titer of 9.1 x 105 TCID50 fish-1 than large fish (20.8 ± 7.5 g) with the mortalities of 92.5% and 12.5%, respectively. Phylogenetic analysis of the concatenated 10 segment coding regions placed two Vietnamese TiLVs (RIA2-VN-2019 and HB196-VN-2020) in a separate clade, distantly related to other reference 21 isolates. Reassortant detection analysis revealed seven potential reassortment events among 23 TiLV genomes, indicating the mixed infection of multiple TiLV isolates at the farms and the fish movement among different regions. However, additional sequences from various sampling locations and times are required to better understand the impacts of genetic diversity and ressortments on the evolution, migration and natural selection of TiLV in Vietnam and other countries.