Screening of freshwater fish species for their susceptibility to a betanodavirus

Abstract

Betanodaviruses, the causative agents of viral nervous necrosis in marine fish, have bipartite positive-sense RNA genomes. Because the genomes are the smallest and simplest among viruses, betanodaviruses have been well studied using a reversed genetics system as model viruses. However, studies of virus-host interactions have progressed slowly because permissive hosts for betanodaviruses (basically larvae and juveniles of marine fish) are only available for limited periods of the year and are not suitable for the construction of a genetic engineering system. To obtain a model fish species that are not subject to these problems, 21 freshwater fish species were injected intramuscularly with a betanodavirus (redspotted grouper nervous necrosis virus) and tested for their susceptibility to the virus. Based on their responses, the tested fish were classified into 3 groups: 4 susceptible fish, 10 less susceptible fish, and 7 resistant fish. The susceptible fish, celebes rainbowfish Telmatherina ladigesi, threadfin rainbowfish Iriatherina werneri, dwarf rainbowfish Melanotaenia praecox, and medaka Oryzias latipes, exhibited erratic swimming and eventually died within 10 d post-inoculation. The virus was specifically localized in the brains, spinal cords, and retinas of the infected fish, similar to the pattern of infection in naturally infected marine fish. We believe that these susceptible freshwater fish species could act as good host models for betanodavirus-fish interaction studies. KEY WORDS: Betanodavirus · Freshwater fish · Model fish · Experimental infection · Medaka · Rainbowfish Resale or republication not permitted without written consent of the publisherDis Aquat Org 77: [119][120][121][122][123][124][125] 2007 tex and tiger puffer Takifugu rubripes, respectively, whereas BFNNV has been isolated from some coldwater species, such as barfin flounder Verasper moseri, Pacific cod Gadus macrocephalus, and Atlantic halibut Hippoglossus hippoglossus. RGNNV has a broad host range and causes disease among a variety of warm water fish species, particularly groupers and sea bass (Munday et al. 2002).Betanodaviruses have key features as model viruses, as is also the case with the insect alphanodaviruses (Ball & Johnson 1998), the other genus of the family Nodaviridae. Betanodaviruses have one of the smallest genomes (4.5 kb in total) among the known viruses, which encode only 3 viral proteins (protein A, CP, and protein B2). Furthermore, a genetic engineering system has already been established based on a cDNAmediated infectious RNA transcription strategy (Iwamoto et al. 2001(Iwamoto et al. , 2004. Qualitative and quantitative analysis of virus multiplication is possible with betanodaviruses, using cultured cells (Frerichs et al. 1996, Chi et al. 1999, Iwamoto et al. 1999, 2000. However, studies of virus-host interactions have progressed slowly because of the limited availability of host fish. Betanodaviruses basically infect marine fish larvae and juveniles, which are only available for a few months of the...

Viruses of Fish: An Overview of Significant Pathogens

“…The virus infects a large range of host species—at least 40 species of marine and freshwater fish world-wide [30]—and the known host range continues to expand as new species of fish are used for aquaculture [38,39]. Of further interest is the potential of wild fish to become sub-clinical carriers as virus-contaminated water spreads from aquaculture enterprises into the marine environment particularly for those countries with large mariculture industries [40].…”

Betanodavirus of Marine and Freshwater Fish: Distribution, Genomic Organization, Diagnosis and Control Measures

“…Infections are also reported in freshwater fish, such as Chinese catfish (P. asotus); Australia catfish (Tandanus tandanus); Barramundi (L. calcarifer); Medaka (Oryzias latipes); guppy (Poicelia reticulata) and zebrafish (Danio rerio) [5,22,52,53,62,63,76]. Several experimental infection studies have demonstrated that both marine and fresh water finfish are susceptible to betanodavirus infection [23,38,39,52,53,63]. It has been seen that Asian seabass juveniles are more susceptible to betanodavirus from 10 day onwards with high mortalities of 80 % and smaller sized fish are more prone to the virus than bigger sized fish in the cages.…”

Phylogenetic Analysis of Betanodavirus RNA2 Identified from Wild Marine Fish in Oceanic Regions

“…In addition, our experimental inoculations of striped jack and sevenband grouper with SJNNV or RGNNV revealed that the two viruses have strict host specificity (Iwamoto et al, 2004). Recently, we tested several ornamental fresh water fish for their susceptibility to an RGNNV isolate and showed that the levels of viral susceptibilities were well correlated with the phylogenetic relationships of tested fish (Furusawa et al, 2007). In this study, the viral sequences obtained were better classified by the origi-nated wild fish species rather than by the sampling locations (Table 2).…”