Role of rotifer (Brachionus plicatilis) andArtemia(Artemia salina) nauplii in the horizontal transmission of a natural nervous necrosis virus (NNV) reassortant strain to Senegalese sole (Solea senegalensis) larvae

Background Marine invertebrates are provided as a first feed for marine fish larvae because of their strict nutritional requirements, despite also being a potential source of infectious agents. Aim To assess horizontal transmission of a nervous necrosis virus reassortant strain (NNV) to sole larvae viaArtemiaand rotifers. Materials and methods Rotifer (Brachionus plicatilis) andArtemia(Artemia salina) nauplii cultures were bath infected with a reassortant (RGNNV/SJNNV) NNV strain isolated from gilthead sea bream and viral internalisation was confirmed by IFA. Senegalese sole (Solea senegalensis) larvae were fed on infectedArtemiaand disease signs and mortality were recorded. In addition, NNV viability was checked in cultures of either unfed invertebrates or invertebrates fed on phytoplankton and in the supernatant of microalgae cultures. All samples were tested by RT-qPCR and inoculation in cell culture. Results Both rotifers andArtemiainternalised NNV. Experimental transmission to sole larvae was achieved using infectedArtemiaand subsequently 60% mortality was recorded. At 24 h post-infection, orally infected individuals contained 9.34 x 10(4)copies of viral RNA, whereas the bath infection yielded 2.05 x 10(6)RNA copies larvae(-1). Viral presence in both invertebrates was detected up to 8 days post infection but viral load decreased over time. Feeding with microalgae decreased viral detection even more and microalgae supernatants were demonstrated to significantly affect NNV viability. Conclusions Our results demonstrate that both invertebrates can bioaccumulate NNV and that Senegalese sole larvae fed on infectedArtemiamight develop viral encephalopathy and retinopathy and high mortality.