Experimental challenge of flatfishes (Pleuronectidae) with salmonid alphavirus (SAV): Observations on tissue tropism and pathology in common dab Limanda limanda L

Salmonid alphavirus (SAV) is the aetiological agent of pancreas disease (PD), a serious viral disease in salmonids. For several decades, SAV was known to infect salmonid species only, until SAV was detected using real-time PCR in several species of wild-caught flatfishes in Scotland in 2010. The presence of SAV in wild flatfishes has been confirmed by further surveys from Ireland and Scotland. The role of flatfishes in SAV-spread and epizootiology has not been elucidated, and no experimental challenges have been conducted to examine virus tissue tropism, virulence and pathology in flatfishes. Wild-caught flatfishes (common dab; Limanda limanda, European plaice; Pleuronectes platessa, European flounder; Platichthys flesus and lemon sole; Microstomus kitt) were either intramuscularly (i.m.) or intraperitoneally (i.p.) challenged with SAV3 or exposed to SAV3 through cohabitation with i.p. injected salmon. SAV-infections were seen in i.m. and i.p. injected dab and i.p. injected salmon but did not result in a transmissible infection in dab although several routes of entry were assessed (oral route not tested). SAV was detected in several tissues of eight common dab (not from cohabitants), with high SAV-levels in pancreas. No viraemia was detected in the SAV-positive common dab and no virus shedding were detected in the tanks. However, pathology in exocrine pancreas and hearts consistent with SAV-replication were seen. This is the first study reporting SAV-induced pathology in a non-salmonid species. The results from the present challenge study supports evidence for common dab being susceptible hosts for SAV. The study also demonstrates that flatfishes are less susceptible to SAV3-infection than salmon.