An inactivated vaccine confers potent and durable protection against a screened virulent rhabdovirus in hybrid snakehead.

Abstract

Hybrid snakehead rhabdovirus (HSHRV) poses a serious threat to hybrid snakehead (Channa maculata &#x2640;&#xa0;&#xd7;&#xa0;C. argus &#x2642;) aquaculture, causing severe outbreaks characterized by high mortality. To develop an effective vaccine, five rhabdovirus strains were isolated from diseased fish across Guangdong Province. Comparative analysis of virulence and host specificity identified a highly pathogenic strain, designated HSHRV-JM0909, which replicated to high titers consistently exceeding 10TCID/mL in mandarin fish brain (MBC) cells. Phylogenetic analysis classified the virus within the genus Siniperhavirus. HSHRV-JM0909 exhibited strong virulence in hybrid snakehead and mandarin fish but was far less pathogenic to largemouth bass, confirming host-specific pathogenicity. The strain maintained stable titers and virulence during serial passage. Using this strain as an antigen, an inactivated vaccine was prepared and formulated with ISA 206, aluminum salt, or GEL 02 adjuvants. Challenge tests at 30 days post-immunization revealed that the ISA 206-adjuvanted vaccine group induced a relative percent survival (RPS) of 91.4%, significantly higher than the non-adjuvanted (78.6%), GEL 02-adjuvanted (37.1%) and aluminum salt-adjuvanted (41.4%) groups (P < 0.05). The ISA 206-adjuvanted vaccine also elicited the highest and most sustained neutralizing antibody response, and maintained 64.7% protection at 90 days post-immunization, without affecting fish growth. This study provides a key vaccine candidate and an optimized adjuvant strategy for controlling hybrid snakehead rhabdovirus disease.