Replication of infectious pancreatic necrosis virus in trout leucocytes and detection of the carrier state

Abstract

Abstract. The exact cellular site of replication of infectious pancreatic necrosis virus (IPNV) in carrier fish is unknown. In order to determine if IPNV replicates in trout leucocytes, we purified leucocytes from normal (non‐carrier) trout and separated the cells into an adherent and a non‐adherent population. IPNV replicated in less than 0‐01 % of the adherent leucocytes with a yield of about 400 p.f.u./cell. IPNV also became associated with less than 0.07% of the non‐adherent leucocytes; either IPNV did not replicate in these cells or the yield was, at best, only a few p.f.u./cell. Trout persistently infected with IPNV (carrier fish) were tested for the presence of IPNV in leucocytes by co‐cultivating with a sensitive fish cell line; this same population of trout was also tested for IPNV by organ sampling using standard methods. Ninety‐eight per cent of the trout were positive for IPNV by organ sampling, but only 75 % yielded IPNV from leucocytes. Thus a blood sample from a living fish can be used to detect the presence of IPNV.