Propidium monoazide PCR, a method to determine OsHV-1 undamaged capsids and to estimate virus Lethal Dose 50.

Ostreid herpes virus 1 (OsHV-1) has been classified within the Malacoherpesviridae family from the Herpesvirales order. OsHV-1 is the etiological agent of a contagious viral disease of Pacific oysters, C. gigas, affecting also other bivalve species.

Evaluation of tangential flow filtration coupled to long-read sequencing for ostreid herpesvirus type 1 genome assembly.

Whole-genome sequencing is widely used to better understand the transmission dynamics, the evolution and the emergence of new variants of viral pathogens. This can bring crucial information to stakeholders for disease management. Unfortunately, aquatic virus genomes are usually difficult to characterize because most of these viruses cannot be easily propagated .

First detection of OsHV-1 in the cephalopod Octopus vulgaris. Is the octopus a dead-end for OsHV-1?

The ostreid herpes virus (OsHV-1), associated with massive mortalities in the bivalve Crassostrea gigas, was detected for the first time in the cephalopod Octopus vulgaris. Wild adult animals from a natural breeding area in Spain showed an overall prevalence of detection of 87.5% between 2010 and 2015 suggesting an environmental source of viral material uptake.

Comparative Proteomics of Ostreid Herpesvirus 1 and Pacific Oyster Interactions With Two Families Exhibiting Contrasted Susceptibility to Viral Infection.

Massive mortality outbreaks affecting Pacific oysters () spat/juveniles are often associated with the detection of a herpesvirus called ostreid herpesvirus type 1 (OsHV-1). In this work, experimental infection trials of spat with OsHV-1 were conducted using two contrasted Pacific oyster families for their susceptibility to viral infection. Live oysters were sampled at 12, 26, and 144 h post infection (hpi) to analyze host-pathogen interactions using comparative proteomics.

First comparison of French and Australian OsHV-1 µvars by bath exposure.

Economically devastating mortality events of farmed and wild shellfish due to infectious disease have been reported globally. Currently, one of the most significant disease threats to Pacific oyster Crassostrea gigas culture is the ostreid herpesvirus 1 (OsHV-1), in particular the emerging OsHV-1 microvariant genotypes. OsHV-1 microvariants (OsHV-1 µvars) are spreading globally, and concern is high among growers in areas unaffected by OsHV-1.

Identification of the autophagy pathway in a mollusk bivalve, Crassostrea gigas.

The Pacific oyster, , is a mollusk bivalve commercially important as a food source. Pacific oysters are subjected to stress and diseases during culture. The autophagy pathway is involved in numerous cellular processes, including responses to starvation, cell death, and microorganism elimination.

Exploring First Interactions Between Ostreid Herpesvirus 1 (OsHV-1) and Its Host, : Effects of Specific Antiviral Antibodies and Dextran Sulfate.

Viral entry mechanisms of herpesviruses constitute a highly complex process which implicates several viral glycoproteins and different receptors on the host cell surfaces. This initial infection stage was currently undescribed for Ostreid herpes virus 1 (OsHV-1), a herpesvirus infecting bivalves including the Pacific oyster, . To identify OsHV-1 glyproteins implicated in the attachment of the virus to oyster cells, three viral putative membrane proteins, encoded by ORF 25, 41, and 72, were selected and polyclonal antibodies against these targets were used to explore first interactions between the virus and host cells.

A study of autophagy in hemocytes of the Pacific oyster, .

Macroautophagy is a mechanism that is involved in various cellular processes, including cellular homeostasis and innate immunity. This pathway has been described in organisms ranging in complexity from yeasts to mammals, and recent results indicate that it occurs in the mantle of the Pacific oyster, . However, the autophagy pathway has never been explored in the hemocytes of , which are the main effectors of its immune system and thus play a key role in the defence of the Pacific oyster against pathogens.

Immune-suppression by OsHV-1 viral infection causes fatal bacteraemia in Pacific oysters.

Infectious diseases are mostly explored using reductionist approaches despite repeated evidence showing them to be strongly influenced by numerous interacting host and environmental factors. Many diseases with a complex aetiology therefore remain misunderstood. By developing a holistic approach to tackle the complexity of interactions, we decipher the complex intra-host interactions underlying Pacific oyster mortality syndrome affecting juveniles of Crassostrea gigas, the main oyster species exploited worldwide.

Contribution of Experimental Challenges to Understanding Flat Oyster Resistance to .

Bonamiosis due to the parasite has been associated with massive mortality outbreaks in European flat oyster stocks in Europe. As eradication and treatment are not possible, the control of the disease mainly relies on transfer restriction. Moreover, selection has been applied to produce resistant flat oyster families, which present better survival and lower prevalence than non-selected oysters.

Haemocytes from Crassostrea gigas and OsHV-1: A promising in vitro system to study host/virus interactions.

Since 2008, mass mortality outbreaks associated with the detection of particular variants of OsHV-1 have been reported in Crassostrea gigas spat and juveniles in several countries. Recent studies have reported information on viral replication during experimental infection. Viral DNA and RNA were also detected in the haemolymph and haemocytes suggesting that the virus could circulate through the circulatory system.

Long dsRNAs promote an anti-viral response in Pacific oyster hampering ostreid herpesvirus 1 replication.

Double-stranded RNA (dsRNA)-mediated genetic interference (RNAi) is a widely used reverse genetic tool for determining the loss-of-function phenotype of a gene. Here, the possible induction of an immune response by long dsRNA was tested in a marine bivalve (), as well as the specific role of the subunit 2 of the nuclear factor κB inhibitor (). This gene is a candidate of particular interest for functional investigations in the context of oyster mass mortality events, as mRNA levels exhibited significant variation depending on the amount of ostreid herpesvirus 1 (OsHV-1) DNA detected.

In situ localization and tissue distribution of ostreid herpesvirus 1 proteins in infected Pacific oyster, Crassostrea gigas.

Immunohistochemistry (IHC) assays were conducted on paraffin sections from experimentally infected spat and unchallenged spat produced in hatchery to determine the tissue distribution of three viral proteins within the Pacific oyster, Crassostrea gigas. Polyclonal antibodies were produced from recombinant proteins corresponding to two putative membrane proteins and one putative apoptosis inhibitor encoded by ORF 25, 72, and 87, respectively. Results were then compared to those obtained by in situ hybridization performed on the same individuals, and showed a substantial agreement according to Landis and Koch numeric scale.

Detection and distribution of ostreid herpesvirus 1 in experimentally infected Pacific oyster spat.

High mortality rates are reported in spat and larvae of Pacific oyster Crassostrea gigas and associated with ostreid herpesvirus 1 (OsHV-1) detection in France. Although the viral infection has been experimentally reproduced in oyster larvae and spat, little knowledge is currently available concerning the viral entry and its distribution in organs and tissues. This study compares OsHV-1 DNA and RNA detection and localization in experimentally infected oysters using two virus doses: a low dose that did not induce any mortality and a high dose inducing high mortality.

Pesticides and Ostreid Herpesvirus 1 Infection in the Pacific Oyster, Crassostrea gigas.

Since 2008, mass mortality outbreaks have been reported in all French regions producing Pacific oysters, and in several Member States of the European Union. These mass mortality events of Pacific oysters are related to OsHV-1 infection. They occur during spring and summer periods leaving suspect the quality of the marine environment and the role of seasonal use of pesticides associated with the arrival of freshwater in oyster rearing areas.

Development of an in situ hybridization assay for the detection of ostreid herpesvirus type 1 mRNAs in the Pacific oyster, Crassostrea gigas.

An in situ hybridization protocol for detecting mRNAs of ostreid herpesvirus type 1 (OsHV-1) which infects Pacific oysters, Crassostrea gigas, was developed. Three RNA probes were synthesized by cloning three partial OsHV-1 genes into plasmids using three specific primer pairs, and performing a transcription in the presence of digoxigenin dUTP. The RNA probes were able to detect the virus mRNAs in paraffin sections of experimentally infected oysters 26 h post-injection.

Ostreid herpesvirus type 1 replication and host response in adult Pacific oysters, Crassostrea gigas.

Since 2008, massive mortality outbreaks associated with OsHV-1 detection have been reported in Crassostrea gigas spat and juveniles in several countries. Nevertheless, adult oysters do not demonstrate mortality in the field related to OsHV-1 detection and were thus assumed to be more resistant to viral infection. Determining how virus and adult oyster interact is a major goal in understanding why mortality events are not reported among adult Pacific oysters.

First description of French V. tubiashii strains pathogenic to mollusk: II. Characterization of properties of the proteolytic fraction of extracellular products.

Extracellular products (ECPs) of the French Vibrio tubiashii strain 07/118 T2 were previously reported to be toxic for the Pacific oyster Crassostrea gigas. In this study we now assessed host cellular immune responses and bacterial potential effectors by which these ECPs can be associated with host damages. The adhesion capacity (28% inhibition) and phagocytosis ability (56% inhibition) of oyster hemocytes were the main functions affected following in vitro contact between hemocytes and V.

Dual transcriptomics of virus-host interactions: comparing two Pacific oyster families presenting contrasted susceptibility to ostreid herpesvirus 1.

Background: Massive mortality outbreaks affecting Pacific oyster (Crassostrea gigas) spat in various countries have been associated with the detection of a herpesvirus called ostreid herpesvirus type 1 (OsHV-1). However, few studies have been performed to understand and follow viral gene expression, as it has been done in vertebrate herpesviruses. In this work, experimental infection trials of C.

Transcriptomic study of 39 ostreid herpesvirus 1 genes during an experimental infection.

Massive mortality outbreaks have been reported in France since 2008 among Pacific oysters, Crassostrea gigas, with the detection of a particular OsHV-1 variant called μVar. Virus infection can be induced in healthy spat in experimental conditions allowing to better understand the disease process, including viral gene expression. Although gene expression of other herpesviruses has been widely studied, we provide the first study following viral gene expression of OsHV-1 over time.

Genotyping of a microsatellite locus to differentiate clinical Ostreid herpesvirus 1 specimens.

Ostreid herpesvirus 1 (OsHV-1) is a DNA virus belonging to the Malacoherpesviridae family from the Herpesvirales order. OsHV-1 has been associated with mortality outbreaks in different bivalve species including the Pacific cupped oyster, Crassostrea gigas. Since 2008, massive mortality events have been reported among C.

Analysis of clinical ostreid herpesvirus 1 (Malacoherpesviridae) specimens by sequencing amplified fragments from three virus genome areas.

Although there are a number of ostreid herpesvirus 1 (OsHV-1) variants, it is expected that the true diversity of this virus will be known only after the analysis of significantly more data. To this end, we analyzed 72 OsHV-1 "specimens" collected mainly in France over an 18-year period, from 1993 to 2010. Additional samples were also collected in Ireland, the United States, China, Japan, and New Zealand.

Cellular and molecular responses of haemocytes from Ostrea edulis during in vitro infection by the parasite Bonamia ostreae.

Bonamia ostreae is a protozoan, affiliated to the order Haplosporidia and to the phylum Cercozoa. This parasite is intracellular and infects haemocytes, cells notably involved in oyster defence mechanisms. Bonamiosis due to the parasite B.

Experimental infection of Pacific oyster Crassostrea gigas spat by ostreid herpesvirus 1: demonstration of oyster spat susceptibility.

In 2008 and 2009, acute mortalities occurred in France among Pacific cupped oyster, Crassostrea gigas, spat. Different hypothesis including the implication of environmental factors, toxic algae and/or pathogens have been explored. Diagnostic tests indicated that OsHV-1 including a particular genotype, termed OsHV-1 μVar, was detected in most of samples and especially in moribund oysters with the highlighting of virus particles looking like herpes viruses by TEM examination.