CHARACTERIZATION OF NOVEL ORTHOMYXOVIRUS CAUSING MASS DIE-OFFS IN TILAPIA

Tilapias are increasingly important to global food security, with global production estimated at 4.5 million metric tons.

Comprising more than 100 species of tilapines, Nile tilapia is the predominant cultured species worldwide. We have previously characterized disease outbreaks, in Israel, among wild and farm-raised fish, characterized by a syndrome comprising lethargy, endopthalmitis, skin erosions, renal congestion and encephalitis. The transmissibility of disease from affected to naïve fish was demonstrated and the agent that was isolated was named Tilapia Lake Virus (TiLV); however, no taxonomic assignment was feasible (Eyngor et al., 2014). Ferguson and coworkers described a disease in farmed Nile tilapia in South America that affected fingerlings and differed in that pathology focused in the liver rather than the central nervous system (Ferguson et al., 2014). No agent was isolated by Ferguson’s group; however, subsequent PCR, using primers and probes based on the sequence obtained from the virus isolated in Israel, revealed the presence of a similar virus.

Here, we report on a comprehensive analysis of TiLV. Unbiased high throughput sequencing (UHTS), northern hybridization, mass spectrometry, in situ hybridization and infectivity studies indicate that TiLV has a segmented, negative-sense RNA genome. TiLV contains 10 genome segments, each with an open reading frame (ORF). Nine of the segments have no recognizable homology to other known sequences; one segment predicts a protein with weak homology to the PB1 subunit of the influenza C virus. Our findings suggest that TiLV represents a novel orthomyxo-like virus and confirm that it poses a global threat to tilapine aquaculture.