First Report of Snakehead Rhabdovirus-Like Novirhabdovirus Associated With Acute Mortality in Multiple Outbreaks in Farmed Giant Snakehead (Channa micropeltes) in Thailand.

Snakehead rhabdovirus (SHRV) is a viral pathogen previously associated with mortality in snakehead fish (Channa spp.) and other closely related species. In this study, we report the detection of SHRV-like virus in giant snakehead (C. micropeltes) from multiple fish farms in Thailand, where acute disease outbreaks resulted in cumulative mortalities ranging from 7% to 90%. The affected fish showed clinical signs, including swimming near the water surface, anorexia, and skin discoloration. Histopathological examination revealed numerous eosinophilic intracytoplasmic inclusion bodies (ICIBs) in the spleen, anterior kidney, and posterior kidney. The virus was successfully isolated in E-11 cells, where it induced marked cytopathic effects (CPEs), including cell rounding, cytoplasmic vacuolization, and progressive monolayer destruction within 1-2 days post-inoculation (dpi). Transmission electron microscopy confirmed the presence of enveloped, bullet-shaped viral particles characteristic of the family Rhabdoviridae. Experimental challenge of naïve giant snakehead with the isolated virus reproduced the clinical signs observed in the field, resulted in 70% cumulative mortality within 4 days, and led to successful re-isolation of the virus from experimentally infected fish, which supports the pathogenic role of the virus in giant snakehead. Reverse-transcription polymerase chain reaction (RT-PCR) and sequence analysis demonstrated that the virus shared 79.70%-85.37% nucleotide identity with previously reported SHRV strains and placed the virus within the genus Novirhabdovirus, forming a cluster with SHRV and Carpione rhabdovirus (CAPRV). These findings provide evidence for the presence of a SHRV-like Novirhabdovirus associated with disease outbreaks in farmed giant snakehead in Thailand and highlight the need for further investigation into its epidemiology, pathogenesis, and transmission dynamics to support the development of effective disease prevention and control strategies.