TWENTY-FIFTH ANNUAL EASTERN FISH HEALTH WORKSHOP MARCH 10-13, 2000   A Unique, Bacilliform, RNA Virus Isolated From Fathead Minnows (Pimephales promelas)     Luke R. Iwanowicz and Andrew E. Goodwin   Aquaculture/ Fisheries Center, University of Arkansas at Pine Bluff, Pine Bluff, AR 71603     During mid-March of 1997, moribund fathead minnows (Pimphales promelas) exhibiting hemorrhages on their eyes and skin were assayed for virus.  Homogenates of whole fathead minnows were prepared and inoculated onto epithelial papilloma cyprini (EPC) cells.  A cytopathic effect (CPE) of multifocal syncytia was observed after a 48 h incubation at 20°C.  A similar CPE was also observed in the fathead minnow (FHM), channel catfish ovary (CCO), brown bullhead (BB), and rainbow trout gonad (RTG-2) cell lines; but not in bluegill fry (BF-2), koi fin (KF-1), or Chinook salmon embryo (CHSE-214) monolayers.  Additionally, a CPE was observed in EPC cells at 15°C, 20°C, and 25°C; but not at 4°C, 30°C, or 35°C.  The filterable agent was inactivated following exposure to 50°C for 10 min, 20% ether, 2 and 50% chloroform, and pH 3 and 10.  The presence of the halogenated pyrimidine, 5’-iodo-2’ deoxyuridine (IDU), had no effect on viral titres.  Electron microscopic examination of negatively stained tissue culture supernatant preparations containing virus revealed slightly pleiomorphic, bacilliform virions 130-180 nm in length and 31-47 nm in diameter.  Immunodot blots performed with antisera against golden shiner virus (GSV), infectious pancreatic necrosis virus (IPNV), spring viremia of carp virus (SVCV), infectious hemorrhagic septicemia virus (IHNV), viral hemorrhagic septicemia virus (VHSV) and pike fry rhabdovirus (PFRV) were all negative.  River’s postulates were fulfilled in fathead minnows, but the agent was not pathogenic in and could not be reisolated from other cyprinids or salmonids during challenge experiments.  Hepatic, splenic, and renal lesions were observed during histological analysis of diseased fathead minnows from the original isolation and challenge studies.  Biochemically and morphologically the isolate resembles an unclassified virus described by Ahne (1988) from grass carp (Ctenopharyngodon idella) which also induces syncytia.  Structural proteins resolved via SDS-PAGE had molecular weights similar to those reported in lyssaviruses of the family Rhabdoviridae; however, syncytia formation is not a typical CPE of rhabdoviruses.  This virus, tentatively designated as the fathead minnow rhabdovirus (FHMRV) may represent a novel agent of a new genus within the Rhabdoviridae; or a possible undescribed taxonomic family of virus.   Return to 25th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page