Experimental infection trials with European North Atlantic ranavirus (Iridoviridae) isolated from lumpfish (Cyclopterus lumpus, L.)

European North Atlantic ranavirus (ENARV, Iridoviridae), is a ranavirus species recently isolated from lumpfish (Cyclopterus lumpus, L.), which are used as cleaner fish in Atlantic salmon (Salmo salar) farming in Northern Europe. This study aimed to investigate (1) the virulence of ENARV isolates from Ireland, Iceland and the Faroe Islands to lumpfish; (2) horizontal transmission between lumpfish; and (3) virulence to Atlantic salmon parr. Lumpfish were challenged in a cohabitation model using intraperitoneally (IP) injected shedders, and naive cohabitants. IP challenge with isolates from Iceland (1.9 x 10(7) TCID50 ml(-1)) and the Faroe Islands (5.9 x 10(7) TCID50 ml(-1)) reduced survival in lumpfish, associated with consistent pathological changes. IP challenge with the Irish strain (8.6 x 10(5) TCID50 ml(-1)) did not significantly reduce survival in lumpfish, but the lower challenge titre complicated interpretation. Horizontal transmission occurred in all strains tested, but no clinical impact was demonstrated in cohabitants. Salmon parr were challenged by IP injection with the Irish isolate, no virulence or virus replication were demonstrated. A ranavirus qPCR assay, previously validated for fish ranaviruses, was first used to detect ENARV in tissues of both in lumpfish and Atlantic salmon. This study provides the first data on the assessment of virulence of ENARV isolates to lumpfish and salmon, guidelines for the diagnosis of ENARV infection, and poses a basis for further investigations into virulence markers.

Automated summary

This study aimed to investigate the virulence of European North Atlantic ranavirus (ENARV) isolates to lumpfish and salmon, as well as horizontal transmission and virus replication. The results showed that different isolates had different virulence to lumpfish, and horizontal transmission was observed, but no clinical impact was demonstrated in cohabitants. Furthermore, the study established guidelines for the diagnosis of ENARV infection and provided a basis for further investigations into virulence markers.