Abstract
Tilapia lake virus (TiLV) is an emerging virus that is rapidly spreading
across the world. Over the past 6 years (2014–2020), TiLV outbreaks had
been reported in at least 16 countries, spanning three continents,
including Asia, Africa, and America. Despite its enormous economic
impact, its origin, evolution, and epidemiology are still largely poorly
characterised. Here, we report eight TiLV whole genome sequences from
Thailand sampled between 2014–2019. Together with publicly available
sequences from various regions of the world, we estimated the origin of
TiLV to be between 2003–2009, 5–10 years before the first report of
the virus in Israel in 2014. Our analyses consistently showed that TiLV
started to spread in 2000s, and reached its peak in 2014–2016, matching
well with the timing of its first report. From 2016 onwards, the TiLV
population declined steadily. This could be a result of herd immunity
building up in the fish population, and / or a reflection of a better
awareness of the virus coupled with a better and more cautious protocol
of Tilapia importation. Despite the fact that we included all publicly
available sequences, our analyses revealed long unsampled histories of
TiLVs in many countries, especially towards its basal diversification.
This result highlights the lack and the need for systematic surveillance
of TiLV in fish.