Detection of Ostreid herpesvirus -1 microvariants in healthy Crassostrea gigas following disease events and their possible role as reservoirs of infection

Evans, Olivia; Hick, Paul; Whittington, Richard J.

doi:10.1016/j.jip.2017.05.004

Cited by 22 publications

(24 citation statements)

References 69 publications

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“…Developing disease resistant oysters takes years to achieve and is an expensive burden for industry [ 82 ], whereas changes to farm husbandry has the undesired economic consequence of reduced growth rates [ 76 , 79 , 80 ]. Observational experiments investigating the impact of OsHV-1 on aquaculture production have observed C. gigas that survived a mortality event in the past appeared to be resistant later in life [ 83 , 84 ]. It also appears this resistance can be passed from generation to generation.…”

Section: Innate Immune Memory and Antiviral Therapeutic Potential mentioning

confidence: 99%

Antiviral Defense and Innate Immune Memory in the Oyster

Green

Speck

2018

Viruses

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The Pacific oyster, Crassostrea gigas, is becoming a valuable model for investigating antiviral defense in the Lophotrochozoa superphylum. In the past five years, improvements to laboratory-based experimental infection protocols using Ostreid herpesvirus I (OsHV-1) from naturally infected C. gigas combined with next-generation sequencing techniques has revealed that oysters have a complex antiviral response involving the activation of all major innate immune pathways. Experimental evidence indicates C. gigas utilizes an interferon-like response to limit OsHV-1 replication and spread. Oysters injected with a viral mimic (polyI:C) develop resistance to OsHV-1. Improved survival following polyI:C injection was found later in life (within-generational immune priming) and in the next generation (multi-generational immune priming). These studies indicate that the oyster’s antiviral defense system exhibits a form of innate immune-memory. An important priority is to identify the molecular mechanisms responsible for this phenomenon. This knowledge will motivate the development of practical and cost-effective treatments for improving oyster health in aquaculture.

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Section: Innate Immune Memory and Antiviral Therapeutic Potential mentioning

confidence: 99%

Antiviral Defense and Innate Immune Memory in the Oyster

Green

Speck

2018

Viruses

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“…Lastly, we assumed that all oysters were susceptible to OsHV-1; in Experiment 3 which was prolonged, susceptible oysters remained after the first mortality event and succumbed in the next. However, there is genetic variation in susceptibility to OsHV-1 within populations of C. gigas [ 44 ] which may explain why some individuals survive repeated exposure to OsHV-1 [ 45 ].…”

Section: Discussionmentioning

confidence: 99%

“…After epizootics in experimental C. gigas that were placed in the Georges River estuary Australia there were survivors that had been exposed to OsHV-1 [ 45 ] and subclinically infected adult C. gigas have also been identified in France [ 52 ]. Although latency is a well known mechanism within herpesvirales [ 2 ] it was not the reason for the epizootic in the Hawkesbury River estuary, Australia as prevalence did not increase between first detection of OsHV-1 in October 2012 and onset of mortality in January 2013 [ 16 ].…”

Section: Discussionmentioning

confidence: 99%

Counting the dead to determine the source and transmission of the marine herpesvirus OsHV-1 in Crassostrea gigas

Whittington

Paul-Pont

Evans

et al. 2018

Vet Res

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Marine herpesviruses are responsible for epizootics in economically, ecologically and culturally significant taxa. The recent emergence of microvariants of Ostreid herpesvirus 1 (OsHV-1) in Pacific oysters Crassostrea gigas has resulted in socioeconomic losses in Europe, New Zealand and Australia however, there is no information on their origin or mode of transmission. These factors need to be understood because they influence the way the disease may be prevented and controlled. Mortality data obtained from experimental populations of C. gigas during natural epizootics of OsHV-1 disease in Australia were analysed qualitatively. In addition we compared actual mortality data with those from a Reed–Frost model of direct transmission and analysed incubation periods using Sartwell’s method to test for the type of epizootic, point source or propagating. We concluded that outbreaks were initiated from an unknown environmental source which is unlikely to be farmed oysters in the same estuary. While direct oyster-to-oyster transmission may occur in larger oysters if they are in close proximity (< 40 cm), it did not explain the observed epizootics, point source exposure and indirect transmission being more common and important. A conceptual model is proposed for OsHV-1 index case source and transmission, leading to endemicity with recurrent seasonal outbreaks. The findings suggest that prevention and control of OsHV-1 in C. gigas will require multiple interventions. OsHV-1 in C. gigas, which is a sedentary animal once beyond the larval stage, is an informative model when considering marine host-herpesvirus relationships.

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“…Two, we confirmed the OsHV‐1 infection by PCR amplification of the catalytic subunit of the viral DNA polymerase (Davison et al., ; Webb et al, ), which is an early gene expressed in infected cells (Segarra et al, ). Three, Evans, Hick, and Whittington () reported that the odds of detecting quantifiable amounts of OsHV‐1 DNA are higher in the gills than in other organs, such as the mantle and adductor muscle. In this study, CgDscam expression was significantly different between mantle and gills; however, the qPCR levels showed a tendency to be lower in mantle, and this difference could be associated with OsHV‐1 abundance.…”

Section: Discussionmentioning

confidence: 99%

Herpes virus OsHV-1 and the protistPerkinsus marinusmodify the expression of the Down syndrome cell adhesion molecule gene in gill and mantle ofCrassostreaspp.

Arzeta-Pino¹,

Acosta

Sarmiento

et al. 2018

Aquac Res

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The Down syndrome cell adhesion molecule (Dscam) gene in invertebrates encodes numerous isoforms derived by alternative splicing as a pathogen-specific response.The role of Dscam in immune system responses has been established in fruit fly, mosquito, shrimp, crab, and crayfish, among other arthropods. In molluscs, this genehas not yet been clearly identified, and more importantly, its function has not been elucidated. The present study examined Dscam expression in Crassostrea gigas (CgDscam) and Crassostrea corteziensis (CcDscam) infected with Ostreid herpesvirus type 1 (OsHV-1) and Perkinsus marinus, respectively, through in situ hybridization and quantitative PCR. The consensus coding sequences for CgDscam and CcDscam showed the same organization of domains identified in other taxonomic groups. Furthermore, conserved regions from the signal peptide to Ig1 and from FNIII6 to the cytoplasmic tail were identified. The Dscam transcript was detected in gills and mantles of both species. The hybridization signals were remarkable in infected tissues.QPCR analysis showed higher Dscam expression levels in the infected gills of both species, but in the mantle, no difference in CgDscam expression was observed between control and infected tissues. Moreover, CcDscam expression was inhibited in infected tissue. These results suggest that Dscam could be directly involved in bivalve immune responses.

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Detection of Ostreid herpesvirus -1 microvariants in healthy Crassostrea gigas following disease events and their possible role as reservoirs of infection

Cited by 22 publications

References 69 publications

Antiviral Defense and Innate Immune Memory in the Oyster

Antiviral Defense and Innate Immune Memory in the Oyster

Counting the dead to determine the source and transmission of the marine herpesvirus OsHV-1 in Crassostrea gigas

Herpes virus OsHV-1 and the protistPerkinsus marinusmodify the expression of the Down syndrome cell adhesion molecule gene in gill and mantle ofCrassostreaspp.

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