Detection and tissue distribution of Ostreid herpesvirus 1 proteins in infected pacific oyster, Crassostrea gigas.

International audienc

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. Real time PCR demonstrated significant differences in terms of viral DNA amounts between the two virus doses. RNA transcripts were detected in oysters receiving the highest dose of viral suspension whereas no transcript was observed in oysters injected with the low dose. This study also allowed observing kinetics of viral DNA and RNA detection in different tissues of oyster spat. Finally, viral detection was significantly different in function of tissues (p < 0.005), time (p < 0.005) with an interaction between tissues and time (p < 0.005) for each probe

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. Positive signals were mainly observed in connective tissue of gills, mantle, adductor muscle, heart, digestive gland, labial palps, and gonads of infected spat. Positive signals were also reported in digestive epithelia. However, few positive signals were also observed in healthy appearing oysters (unchallenged spat) and could be due to virus persistence after a primary infection. Cellular localization of staining seemed to be linked to the function of the viral protein targeted. A nucleus staining was preferentially observed with antibodies targeting the putative apoptosis inhibitor protein whereas a cytoplasmic localization was obtained using antibodies recognizing putative membrane proteins. The detection of viral proteins was often associated with histopathological changes previously reported during OsHV-1 infection by histology and transmission electron microscopy. Within the 6h after viral suspension injection, positive signals were almost at the maximal level with the three antibodies and all studied organs appeared infected at 28h post viral injection. Connective tissue appeared to be a privileged site for OsHV-1 replication even if positive signals were observed in the epithelium cells of different organs which may be interpreted as a hypothetical portal of entry or release for the virus. IHC constitutes a suited method for analyzing the early infection stages of OsHV-1 infection and a useful tool to investigate interactions between OsHV-1 and its host at a protein leve

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

International audienceSince 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. Dual transcriptomics of virus-host interactions were explored by real-time PCR in adult oysters after a virus injection. Thirty-nine viral genes and five host genes including MyD88, IFI44, IkB2, IAP and Gly were measured at 0.5, 10, 26, 72 and 144 hours post infection (hpi). No viral RNA among the 39 genes was detected at 144 hpi suggesting the adult oysters are able to inhibit viral replication. Moreover, the IAP gene (oyster gene) shows significant up-regulation in infected adults compared to control adults. This result suggests that over-expression of IAP could be a reaction to OsHV-1 infection, which may induce the apoptotic process. Apoptosis could be a main mechanism involved in disease resistance in adults. Antiviral activity of haemolymph against herpes simplex virus (HSV-1) was not significantly different between infected adults versus control

The Viral Hemorrhagic Septicemia Virus (VHSV) Markers of Virulence in Rainbow Trout (Oncorhynchus mykiss)

International audienceViral hemorrhagic septicemia virus (VHSV) is a highly contagious virus leading to high mortality in a large panel of freshwater and marine fish species. VHSV isolates originating from marine fish show low pathogenicity in rainbow trout. The analysis of several nearly complete genome sequences from marine and freshwater isolates displaying varying levels of virulence in rainbow trout suggested that only a limited number of amino acid residues might be involved in regulating the level of virulence. Based on a recent analysis of 55 VHSV strains, which were entirely sequenced and phenotyped in vivo in rainbow trout, several amino acid changes putatively involved in virulence were identified. In the present study, these amino acid changes were introduced, alone or in combination, in a highly-virulent VHSV 23-75 genome backbone by reverse genetics. A total of 35 recombinant VHSV variants were recovered and characterized for virulence in trout by bath immersion. Results confirmed the important role of the NV protein (R116S) and highlighted a major contribution of the nucleoprotein N (K46G and A241E) in regulating virulence. Single amino acid changes in these two proteins drastically affect virus pathogenicity in rainbow trout. This is particularly intriguing for the N variant (K46G) which is unable to establish an active infection in the fins of infected trout, the main portal of entry of VHSV in this species, allowing further spread in its host. In addition, salmonid cell lines were selected to assess the kinetics of replication and cytopathic effect of recombinant VHSV and discriminate virulent and avirulent variants. In conclusion, three major virulence markers were identified in the NV and N proteins. These markers explain almost all phenotypes (92.7%) observed in trout for the 55 VHSV strains analyzed in the present study and herein used for the backward validation of virulence markers. The identification of VHSV specific virulence markers in this species is of importance both to predict the in vivo phenotype of viral isolates with targeted diagnostic tests and to improve prophylactic methods such as the development of safer live-attenuated vaccines

Episodes de mortalité massive de moules bleues observés en 2014 dans les Pertuis charentais

Mass mortality outbreaks (90-100%) in both juvenile and adult blue mussels were reported in 2014 along the Pertuis Charentais area of the French Atlantic coast. A series of studies were carried out to learn more about the phenomenon through detecting pathogens, describing environmental conditions and establishing the physiological status of the animals. Bacteria identif ied as belonging to the V. splendidus species were detected in dying mussels and seem able to cause mortality in blue mussels in the laboratory. Unusual environmental conditions (large amounts of fresh water, re-suspension of sediments during a series of storms, and a high renewal rate of specific water masses in Brittany’s Pertuis area) may be partially responsible for sparking the phenomenDes épisodes de mortalité massive (90-100 %) ont été observés au sein des élevages de moules touchant à la fois les animaux adultes et les juvéniles au printemps 2014, dans les Pertuis charentais. Un ensemble de travaux a été réalisé afin d’analyser et de mieux comprendre ce phénomène en recherchant la présence d’agents infectieux, en décrivant les fluctuations environnementales associées et en étudiant l’état physiologique des animaux. Des bactéries identifiées comme appartenant à l’espèce V. splendidus ont été détectées chez les animaux moribonds et apparaissent capables d’induire des mortalités en laboratoire chez les moules bleues. De plus, des conditions environnementales particulières (apports importants d’eau douce, remise en suspension de sédiments au travers de tempêtes successives et temps de renouvellement des masses d’eau spécifiques du Pertuis breton élevé) ont été associées au déclenchement du phénomèn

Surmortalités de la moule bleue Mytilus edulis dans les Pertuis Charentais (mars 2014)

Suite aux surmortalités observées au sein des élevages de moules touchant à la fois les animaux adultes et les juvéniles au mois de mars, dans les Pertuis Charentais, la Direction Générale de l’Alimentation (DGAl) a adressé une saisine à Ifremer le 04 avril 2014. Celle-ci fait état d’une demande d’appui scientifique et technique d’Ifremer pour tenter d’apporter des éléments de réponse par rapport à cette mortalité subite et importante. L’Ifremer a proposé un projet d’action permettant l’expertise du phénomène de surmortalité de la moule bleue, selon 3 axes : l’impact environnemental, la pathologie et les caractéristiques physiologiques des moules. Il s’agit de mettre en évidence la présence ou non d’agents infectieux connus ou émergents, d’apporter des éléments de compréhension au regard des fluctuations environnementales, de la réponse physiologique et biochimique des moules dans la mer des Pertuis Charentais et des interactions entre ces trois volets

Transcriptional reprogramming from innate immune functions to a pro-thrombotic signature by monocytes in COVID-19

Although myeloid cell dysfunction has been observed in COVID-19, the underlying mechanisms remain incompletely understood. Here, the authors demonstrate that monocytes from patients with mild to moderate COVID-19 show a blunted innate immune response and a pro-thrombotic signature following secondary SARS-CoV-2 challenge

PERLE - Programme d'expérimentation et de recherche sur l'huître plate Ostrea edulis - Rapport final des sous-programmes 2 et 3

L’huître plate (Ostrea edulis) est une espèce endémique des côtes européennes, elle est présente depuis des millions d’années. Son aire de répartition est très vaste allant de la Norvège jusqu’au Maroc. Elle est également présente en mer Méditerranée, en mer Noire, mais également au Canada, aux Etats-Unis ou encore en Afrique du Sud, à la suite d'introductions pour des raisons aquacoles. En France, à partir de la fin des années 70, de fortes mortalités ont été constatées sur les bancs naturels et en élevage, faisant rapidement chuter la production de 20 000 tonnes à 2 000 tonnes. Ces mortalités ont été attribuées à deux maladies parasitaires : la marteiliose (due au parasite Marteilia refringens) et la bonamiose (due au parasite Bonamia ostreae). Trente ans après, les niveaux de production n’ont jamais rattrapé les niveaux des années 60 et stagnent autour de 1 500 tonnes par an. C’est dans ce contexte difficile pour l’huître plate additionné à la crise des mortalités massives sur la production de l’huître creuse (Crassostrea gigas) que le programme PERLE est né pour relancer une production viable d’huîtres plates dans un souci de diversification des activités conchylicoles dans le grand ouest, et la volonté de pérenniser une production ancestrale. PERLE a fédéré professionnels conchylicoles représentés par les CRC Bretagne-Nord et Pays de la Loire, scientifiques d’Ifremer, du CNRS et de l’IUEM ainsi que le centre technique du SMIDAP autour de la problématique de la restauration des bancs naturels d’huîtres plates