Dataset Information

Phenotypic diversity of infectious red sea bream iridovirus isolates from cultured fish in Japan.

ABSTRACT: Megalocytivirus is causing economically serious mass mortality by infecting fish in and around the Pacific region of Asia. The recent emergence of many new iridoviruses has drawn attention to the marked taxonomic variation within this virus family. Most studies of these viruses have not included extensive study of these emergent species. We explored the emergence of red sea bream iridovirus (RSIV) on a fish farm in Japan, and we specifically endeavored to quantify genetic and phenotypic differences between RSIV isolates using in vitro and in vivo methods. The three isolates had identical major capsid protein sequences, and they were closely related to Korean RSIV isolates. In vitro studies revealed that the isolates differed in replication rate, which was determined by real-time quantitative PCR of viral genomes in infected cells and cell culture supernatant, and in cell viability, estimated by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay for infected cells. In vivo studies showed that the isolates exhibit different virulence characteristics: infected red sea bream showed either acute death or subacute death according to infection with different isolates. Significant differences were seen in the antigenicity of isolates by a formalin-inactivated vaccine test. These results revealed that variant characteristics exist in the same phylogenetic location in emergent iridoviruses. We suggest that this strain variation would expand the host range in iridoviral epidemics.

SUBMITTER: Shinmoto H

PROVIDER: S-EPMC2687316 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature

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Phenotypic diversity of infectious red sea bream iridovirus isolates from cultured fish in Japan.

Shinmoto Hajime H Taniguchi Ken K Ikawa Takuya T Kawai Kenji K Oshima Syun-ichirou S

Applied and environmental microbiology 20090403 11

Megalocytivirus is causing economically serious mass mortality by infecting fish in and around the Pacific region of Asia. The recent emergence of many new iridoviruses has drawn attention to the marked taxonomic variation within this virus family. Most studies of these viruses have not included extensive study of these emergent species. We explored the emergence of red sea bream iridovirus (RSIV) on a fish farm in Japan, and we specifically endeavored to quantify genetic and phenotypic differen ...[more]

PMID: 19346349

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Project description:ABSTRACT Red sea bream iridoviral disease (RSIVD) causes high economic damage in mariculture in Asian countries. However, there is little information on the source of infection and viral dynamics in fish farms. In the present study, the dynamics of RSIV in a fish farm that mainly reared juveniles and broodstocks of red sea bream (Pagrus major) were monitored over 3 years (2016 to 2018) by targeting environmental DNA (eDNA) of seawater. Our monitoring demonstrated that red sea bream iridovirus (RSIV) was detected from the eDNA at least 5 days before an RSIVD outbreak in the juveniles. The viral loads of eDNA during the outbreak were highly associated with the numbers for daily mortality, and they reached a peak of 106 copies/liter seawater in late July in 2017, when daily mortality exceeded 20,000 fish. In contrast, neither clinical signs nor mortality was observed in the broodstocks during the monitoring periods, whereas the broodstocks were confirmed to be virus carriers by an inspection in October 2017. Interestingly, the viral load of eDNA in the broodstock net pens (105 copies/liter seawater) was higher than that in the juvenile net pens (104 copies/liter seawater) just before the RSIVD outbreak in late June 2017. After elimination of all RSIV-infected surviving juveniles and 90% of broodstocks, few RSIV copies were detected in the eDNA in the fish farm from April 2018 onward (fewer than 102 copies/liter seawater). These results imply that the virus shed from the asymptomatically RSIV-infected broodstock was transmitted horizontally to the juveniles and caused further RSIVD outbreaks in the fish farm. IMPORTANCE Environmental DNA (eDNA) could be applied in monitoring waterborne viruses of aquatic animals. However, there are few data for practical application of eDNA in fish farms for the control of disease outbreaks. The results of our field research over 3 years targeting eDNA in a red sea bream (Pagrus major) fish farm implied that red sea bream iridoviral disease (RSIVD) outbreaks in juveniles originated from virus shedding from asymptomatically virus-infected broodstocks. Our work identifies an infection source of RSIVD in a fish farm via eDNA monitoring, and it could be applied as a tool for application in aquaculture to control fish diseases.

Project description:Lymphocystis disease is a geographically widespread disease affecting more than 150 different species of marine and freshwater fish. The disease, provoked by the iridovirus lymphocystis disease virus (LCDV), is characterized by the appearance of papillomalike lesions on the skin of affected animals that usually self-resolve over time. Development of the disease is usually associated with several environmental factors and, more frequently, with stress conditions provoked by the intensive culture conditions present in fish farms. In gilthead sea bream (Sparus aurata), an economically important cultured fish species in the Mediterranean area, a distinct LCDV has been identified but not yet completely characterized. We have used direct sequencing of the virome of lymphocystis lesions from affected S. aurata fish to obtain the complete genome of a new LCDV-Sa species that is the largest vertebrate iridovirus sequenced to date. Importantly, this approach allowed us to assemble the full-length circular genome sequence of two previously unknown viruses belonging to the papillomaviruses and polyomaviruses, termed Sparus aurata papillomavirus 1 (SaPV1) and Sparus aurata polyomavirus 1 (SaPyV1), respectively. Epidemiological surveys showed that lymphocystis disease was frequently associated with the concurrent appearance of one or both of the new viruses. SaPV1 has unique characteristics, such as an intron within the L1 gene, and as the first member of the Papillomaviridae family described in fish, provides evidence for a more ancient origin of this family than previously thought.Lymphocystis disease affects marine and freshwater fish species worldwide. It is characterized by the appearance of papillomalike lesions on the skin that contain heavily enlarged cells (lymphocysts). The causative agent is the lymphocystis disease virus (LCDV), a large icosahedral virus of the family Iridoviridae In the Mediterranean area, the gilthead sea bream (Sparus aurata), an important farmed fish, is frequently affected. Using next-generation sequencing, we have identified within S. aurata lymphocystis lesions the concurrent presence of an additional LCDV species (LCDV-Sa) as well as two novel viruses. These are members of polyomavirus and papillomavirus families, and here we report them to be frequently associated with the presence of lymphocysts in affected fish. Because papillomaviruses have not been described in fish before, these findings support a more ancient origin of this virus family than previously thought and evolutionary implications are discussed.

Dataset Information

Phenotypic diversity of infectious red sea bream iridovirus isolates from cultured fish in Japan.

Publications

Phenotypic diversity of infectious red sea bream iridovirus isolates from cultured fish in Japan.

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