Sleeping disease (SD) is currently a matter of concern for salmonid fish farmers in most parts of the world. A viral etiology of SD has recently been suspected, since virus-like particles have been observed in infected rainbow trout cells. In salmonid-derived cell lines, the maximal rate of virus production was observed at 10°C, while little virus was produced at 14°C. Through biochemical, physicochemical, and morphological studies, SD virus (SDV) was shown to be an enveloped virus of roughly 60 nm in diameter. The genome consists of 12 kb of RNA, with the appearance of a 26S subgenomic RNA during the time course of SDV replication. The screening of a random-primed cDNA library constructed from the genomic RNA of semipurified virions facilitated the identification of a specific SDV cDNA clone having an open reading frame related to the alphavirus E2 glycoproteins. To extend the comparison between SDV structural proteins and the alphavirus protein counterparts, the nucleotide sequence of the total 4.1-kb subgenomic RNA has been determined. The 26S RNA encodes a 1,324-amino-acid polyprotein exhibiting typical alphavirus structural protein organization. SDV structural proteins showed several remarkable features compared to other alphaviruses: (i) unusually large individual proteins, (ii) very low homology (ranging from 30 to 34%) (iii) an unglycosylated E3 protein, and (iv) and E1 fusion domain sharing mutations implicated in the pH threshold. Although phylogenetically related to the Semliki Forest virus group of alphaviruses, SDV should be considered an atypical member, able to naturally replicate in lower vertebrates.Sleeping disease (SD) syndrome of farmed freshwater rainbow trout has been observed in France for many years (4). The most characteristic sign of the disease is the unusual behavior of the fish, which stay on their side at the bottom of the tank. Histological observations of diseased fish showed a chronological appearance of lesions in the pancreas, in the heart, and in the muscle at the last stage of the disease (5, 6). Transmission of SD may occur through contact with contaminated tissue from fish that have SD (5). A viral etiology of SD was suspected, since virus-like particles were observed in purified homogenates from kidneys of diseased fish (3). However, all attempts to isolate a viral agent on commonly available fish cell lines by inoculating organ homogenates from diseased fish remained unsuccessful until recently (7). Isolation of SD virus (SDV) in cell culture was successfully achieved by direct inoculation of salmonid cell lines (CHSE-214 and RTG-2) with plasma from infected fish.The characterization of SDV was successfully achieved by optimizing viral production in tissue culture and by studying several physicochemical features of this virus. Data include the type of nucleic acid, size, and organization of the SDV genome. The viral genome has been shown to be an RNA molecule of roughly 12 kb. A cDNA library has been constructed, and the nucleotide sequencing of recombinant cDNA clones de...

No abstract

No abstract

The transmission of vlral encephalopathy and retinopathy (VER) was investigated In juvenlle sea bass (3 g ) D~centrarchus labrax by using cell culture supernatant (SSN-1 cell llne) containing nodavirus F~v e methods of infection were tested intramuscular ~n]ection (IM), intraper~toneal inlection (IP) oral Infection bath exposure and cohabitation of healthy flsh with infected fish Some differences were observed in time of disease onset and seventy of symptoms depending on the mode of infect~on used C h n~c a l symptoms such as w h~r h n g swmming and lethargic or hyperactive behavlour were generally reproduced, except for fish infected vla oral and IP infection First mortalit~es occurred 3 d after IM and IP infection and 6 d after for the other modes of infection Cumulative mortal~ties were also vanable 100% after IM infect~on, 10% after IP infection 32",, for bath exposure 43% after cohab~tatlon and 24% vla oral infect~on Histopatholog~cally vacuolation was observed in the central nervous tlssues and in the retina The observed lesions were more or less severe depending on the mode of Infection, the sampllng t~m e and the organs leslons on the surviving flsh (42 days post infection d p i ) seemed to be generally more conspicuous in the retina than in the brain of the same fish In most cases, the presence of nodavirus was conf~rmed in the same samples of brain and retina by ~mmunohistochemistry and reverse transcnptase-polymerase c h a~n reactlon (RT-PCR) The virus was not detected In other organs e x a m n e d The present results suggest that 2 forms of VER can b e Induced IM inlectlon leads to a n acute form (severe nervous disorders m t h high and fast n~ortality) whereas oral infect~on bath exposure and cohabitation Induce a subacute form (less severe disorders and weak dally mortality) This experlrnent demonstrates expenmentally induced honzontal transmission of VER in sea bass for the first t~m e

A betanodavirus associated with a massive mortality was isolated from larvae of tilapia, Oreochromis niloticus, maintained in fresh water at 30 degrees C. Histopathology revealed vacuolation of the nervous system, suggesting an infection by a betanodavirus. The virus was identified by indirect fluorescent antibody test in the SSN1 cell line and further characterized by sequencing of a PCR product. Sequencing of the T4 region of the coat protein gene indicated a phylogenetic clustering of this isolate within the red-spotted grouper nervous necrosis virus type. However, the tilapia isolate formed a unique branch distinct from other betanodavirus isolates. The disease was experimentally reproduced by bath infection of young tilapia at 30 degrees C. The reservoir of virus at the origin of the outbreak remains unidentified. To our knowledge, this is the first report of natural nodavirus infection in tilapia reared in fresh water.

Abstract. Rainbow trout (Oncorhynchus mykiss) were bath challenged with viral hemorrhagic septicemia (VHS) virus or infectious hematopoietic necrosis (IHN) virus or with both viruses simultaneously. The viral distribution and development of histologic lesions were examined using immunohistochemistry, while virus titer in kidney was determined by viral titration in cell culture. Single infections with VHS virus and IHN virus showed similar distributions of virus in internal organs. The early identification of virus in gill epithelium, 1 and 2 days postinfection (PI) for VHS virus and IHN virus, respectively, indicates that this organ is the point of entry for both viruses. The detection of VHS virus at 1 day PI and 3 days PI for IHN virus is indicative of kidney and spleen being the target organs for these viruses. A simultaneous infection of VHS virus and IHN virus resulted in both viruses establishing an infection. Further double infection did not result in a statistically significant lower titer of both viruses in kidney but a more restricted distribution of IHN virus in internal organs compared with the single infected group. The most striking finding is that, for IHN virus, virus was not detected in the brain in situ in the double-infected group. This study provides support for the conclusion that simultaneous infection with two piscine rhabdoviruses in a susceptible host results in some degree of interaction at the cell level, leading to a reduced systemic distribution of IHN virus.

No abstract

Despite the increasing impact of rhabdoviruses in European percid farming, the diversity of the viral populations is still poorly investigated. To address this issue, we sequenced the partial nucleoprotein (N) and complete glycoprotein (G) genes of nine rhabdoviruses isolated from perch (Perca fluviatilis) between 1999 and 2010, mostly from France, and analyzed six of them by immunofluorescence antibody test (IFAT). Using two rabbit antisera raised against either the reference perch rhabdovirus (PRhV) isolated in 1980 or the perch isolate R6146, two serogroups were distinguished. Meanwhile, based on partial N and complete G gene analysis, perch rhabdoviruses were divided into four genogroups, A-B-D and E, with a maximum of 32.9% divergence (G gene) between isolates. A comparison of the G amino acid sequences of isolates from the two identified serogroups revealed several variable regions that might account for antigenic differences. Comparative analysis of perch isolates with other rhabdoviruses isolated from black bass, pike-perch and pike showed some strong phylogenetic relationships, suggesting cross-host transmission. Similarly, striking genetic similarities were shown between perch rhabdoviruses and isolates from other European countries and various ecological niches, most likely reflecting the circulation of viruses through fish trade as well as putative transfers from marine to freshwater fish. Phylogenetic relationships of the newly characterized viruses were also determined within the family Rhabdoviridae. The analysis revealed a genetic cluster containing only fish viruses, including all rhabdoviruses from perch, as well as siniperca chuatsi rhabdovirus (SCRV) and eel virus X (EVEX). This cluster was distinct from the one represented by spring viraemia of carp vesiculovirus (SVCV), pike fry rhabdovirus (PFRV) and mammalian vesiculoviruses. The new genetic data provided in the present study shed light on the diversity of rhabdoviruses infecting perch in France and support the hypothesis of circulation of these viruses between other hosts and regions within Europe.