Establishment of an in vivo screening platform for anti-nervous necrosis virus drugs

Nervous necrosis virus (NNV), which belongs to the betanodavirus of the Nodaviridae family, is the causative agent of viral nervous necrosis (VNN). It is one of the major viral diseases of hatchery-reared grouper in Taiwan. The infection often causes more than 95% of mortality during larval stage of grouper. Therefore, it is important to develop an anti-NNV drug to prevent virus infection. In order to develop an in vivo screening platform, zebrafish and medaka in different stages are investigated by intra-peritoneal (i.p.) injection or immersion with virus. Results show that the adult medaka but not zebrafish appears erratic swimming and death. In larvae bath infection, the mean relative percent survival (RPS) of medaka infecting NNV at 1, 7, 14, 21, and 28 day-post-hatch (d.p.h.) was 49%, 33%, 55%, 60% and 89%, respectively, after 2 weeks of infection. The mean RPS of zebrafish infecting at 1 d.p.h. was 92% after 2 weeks of infection. Because the medaka is a euryhaline teleost, medaka larvae of 1 d.p.h. infected by NNV in seawater condition show the mean RPS of 40% after 2 weeks of infection. We suggest that 1 d.p.h. medaka larvae are more suitable to establish an in vivo screening platform for an anti-NNV drug.