Tilapia lake virus: A structured phylogenetic approach.

Area of Science:

• Aquatic Virology
• Fish Pathology
• Molecular Epidemiology

Background:

• Tilapia Lake Virus (TiLV) is an emerging viral pathogen impacting tilapia (Oreochromis spp.), a crucial global food source.
• TiLV outbreaks, first reported in 2014, have led to high mortality rates (up to 90%) and significant socio-economic losses.
• Limited availability of complete TiLV genomes hinders comprehensive understanding of its origin, evolution, and spread.

Purpose of the Study:

• To identify, isolate, and perform complete genome sequencing of TiLV from Israeli outbreaks in 2018.
• To characterize genetic segments of TiLV using a bioinformatics approach.
• To conduct phylogenetic analysis and investigate potential viral reassortment events.

Main Methods:

• Isolation and complete genome sequencing of two TiLV strains from Israeli tilapia farms.
• Bioinformatic analysis of viral genetic segments.
• Phylogenetic analysis using concatenated ORFs 1, 3, and 5.
• Investigation of reassortment events in TiLV isolates.

Main Results:

• Complete genome sequences of two Israeli TiLV isolates were obtained.
• Phylogenetic analysis using concatenated ORFs 1, 3, and 5 provided reliable tree topology.
• A reassortment event was identified in segment 3 of the TiLV/Israel/939-9/2018 isolate.
• Previous reassortment events in other isolates were confirmed.

Conclusions:

• The study provides complete TiLV genomes, enhancing knowledge of its genetic makeup.
• Phylogenetic analysis using specific ORFs is effective for TiLV studies.
• The findings confirm reassortment as a factor in TiLV evolution and epidemiology.
• Further research is needed to fully elucidate the impact of reassortment on TiLV virulence and spread.