CHARACTERIZATION OF A RHABDOVIRUS ISOLATED FROM CARPIONE SALMO-TRUTTACARPIO IN ITALY

A virus, strain 583, was isolated from carpione Salmo trutta carpio fr y exhibiting high mortality. The virus was not neutralized by rabbit a ntisera against the fish rhabdbviruses viral haemorrhagic septicaemia virus (VHSV), infectious hematopoietic necrosis virus, eel rhabdovirus European X, spring viraemia of carp virus or pike fry rhabdovirus, or against the birnavirus infectious pancreatic necrosis virus. The viru s replicated in several fish cell lines incubated at 20 to 25 degrees C and grew optimally in the bluegill fry (BF-2) and fathead minnow (FH M) cell lines. Electron microscopy of infected BF-2 cell cultures reve aled the presence of typical rhabdovirus particles, and immunofluoresc ent staining was observed using various polyclonal and monoclonal anti bodies (MAbs) against Egtved virus, the causative agent of viral haemo rrhagic septicaemia. The staining by a MAb against the nucleoprotein ( N) of VHSV was particularly strong, a MAb against the glycoprotein (G) gave a moderate reaction, whereas a second MAb against the G protein and MAbs against the matrix proteins, M(1) and M(2), of VHSV did not r eact. Fluorescence titres using 3 rabbit antisera against whole Egtved virus varied between negative and moderately positive. Western blotti ng using polyclonal and monoclonal sera confirmed that both the N and G proteins of the carpione virus shared some epitopes with those of VH SV, but the M(1) and M(2) proteins did not. SDS-PAGE showed the struct ural proteins of the carpione virus produced a pattern typical of memb ers of the Lyssavirus genus of the Rhabdoviridae and the molecular wei ghts were very similar to those of VHSV, except for the M(2) protein w hich was somewhat smaller. Infection trials showed the carpione virus induced high mortalities in carpione fry but not in rainbow trout Onco rhynchus mykiss fry. The carpione virus was clearly distinguishable fr om Egtved virus despite limited serological cross reaction. Since it w as also easily distinguishable by immunofluorescence from the other fi sh rhabdoviruses included in the present study as well as in studies p ublished elsewhere, it is concluded that the virus is a previously und escribed one. It is proposed that the virus be given the preliminary d esignation 'carpione rhabdovirus'.