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The parasitic species Perkinsus olseni (= atlanticus) (Perkinsea, Alveolata) infects a wide range of mollusc species and is responsible for mortality events and economic losses in the aquaculture industry and fisheries worldwide. Thus far, most studies conducted in this field have approached the problem from a “one parasite-one disease” perspective, notably with regards to commercially relevant clam species, while the impact of other Perkinsus species should also be considered as it could play a key role in the disease phenotype and dynamics. Co-infection of P. olseni and P. chesapeaki has already been sporadically described in Manila clam populations in Europe. Here, we describe for the first time the parasitic distribution of two Perkinsus species, P. olseni and P. chesapeaki, in individual clam organs and in five different locations across Arcachon Bay (France), using simultaneous in situ detection by quantitative PCR (qPCR) duplex methodology. We show that P. olseni single-infection largely dominated prevalence (46–84%) with high intensities of infection (7.2 to 8.5 log-nb of copies. g−1of wet tissue of Manila clam) depending on location, suggesting that infection is driven by the abiotic characteristics of stations and physiological states of the host. Conversely, single P. chesapeaki infections were observed in only two sampling stations, Ile aux Oiseaux and Gujan, with low prevalences 2 and 14%, respectively. Interestingly, the co-infection by both Perkinsus spp., ranging in prevalence from 12 to 34%, was distributed across four stations of Arcachon Bay, and was detected in one or two organs maximum. Within these co-infected organs, P. olseni largely dominated the global parasitic load. Hence, the co-infection dynamics between P. olseni and P. chesapeaki may rely on a facilitating role of P. olseni in developing a primary infection which in turn may help P. chesapeaki infect R. philippinarum as a reservoir for a preferred host. This ecological study demonstra

The haplosporidian parasites Bonamia ostreae (BO) and B. exitiosa (BE) are serious oyster pathogens. Two independent laboratories evaluated fluorescence real-time loop-mediated isothermal amplification (LAMP) assays for rapidly detecting these parasites. Specific LAMP assays were designed on the BO actin-1 and BE actin genes. A further generic assay was conceived on a conserved region of the 18S gene to detect both Bonamia species. The optimal reaction temperature varied from 65 to 67 °C depending on the test and instrument. Melting temperatures were 89.8–90.2 °C, 87.0–87.6 °C, and 86.2–86.6 °C for each of the BO, BE, and generic assays. The analytical sensitivity of these assays was 50 copies/µL in a 30 min run. The BO and BE test sensitivity was ~1 log lower than a real-time PCR, while the generic test sensitivity was similar to the real-time PCR. Both the BO and BE assays were shown to be specific; however, the generic assay potentially cross-reacts with Haplosporidium costale. The performance of the LAMP assays evaluated on samples of known status detected positives within 7–20 min with a test accuracy of 100% for the BO and generic tests and a 95.8% accuracy for BE. The ease of use, rapidity and affordability of these tests allow for field deployment.

The “International symposium on ecology and evolution of marine parasites and diseases” is a unique meeting combining marine ecology and parasitology. Considering the need to integrate parasitology in ecosystem studies and global change scenarios, this symposium provides a great opportunity to present the latest research findings regarding marines parasites, to gather international experts from various disciplines and to identify next research priorities in this area, both at the European and international levels. The symposium included seven sessions spread over 3 days on parasites affecting marine organisms: parasite adaptation and evolution, biogeopgraphy and macroecology, parasite detection, disease impact and management, epidemiology, environmental parasitology. A workshop focusing on micro-parasites of bivalves was also organised on the 4th day and was opened to interested participants. The symposium was held at "Espace Encan" in La Rochelle, on the 15th-18th of November 2022. The 7 sessions were also available remotely through the Imagina application: https://app.imagina.com/marine-parasitology-symposium A total of 123 participants from 22 differents countries attended the Symposium. The scientific committee : - Dr. Isabelle Arzul, IFREMER, France - Dr. David W. Thieltges, Royal Netherlands Institute for Sea Research, The Netherlands - Dr. Mathias Wegner, Alfred Wegener Institute, Germany - Pr. Xavier de Montaudouin, University of Bordeaux, France The organizing committee: IFREMER, Adaptation and health of marine invertabrates Unit (ASIM), La Tremblade, France - Isabelle Arzul, Isabelle.Arzul@ifremer.fr - Lydie Canier,Lydie.Canier@ifremer.fr - Véronique Betto, Veronique.Betto@ifremer.fr The Sponsors: This event has received funding from Ifremer, the Aquitaine Region, the Communauté d'Agglomération de La Rochelle, UMR EPOC/University of Bordeaux, and the European Union Reference Laboratory for Molluscs Diseases.

In the fifty years since the introduction of the Pacific oyster Crassostrea gigas and the first reports of the parasites Marteilia refringens and Bonamia ostreae in European waters, numerous research projects dedicated to the native European flat oyster Ostrea edulis have been conducted, notably in France. Most of these projects have been dedicated to developing controlled reproduction and hatchery technology for seed production, examining pathological aspects to understand and control diseases, and using genetics to develop resistant lines. While the long-term objective of most studies has been to revive the aquaculture production of O. edulis, a smaller number have addressed the ecology of local remnant beds and reefs in France. This article provides an overview of the major outcomes of all these projects, focusing on results obtained in France and prospects for future work there, taking into account the rising interest in increasing aquaculture production and ecological motivation to restore declining populations as part of the framework of the Native Oyster Restoration Alliance (NORA) and in line with UN Decade for Ecosystem Restoration.

Vector or reservoir species of five fish diseases listed in the Animal Health Law were identified, based on evidence generated through an extensive literature review (ELR), to support a possible updating of Regulation (EU) 2018/1882. Fish species on or in which highly polymorphic region-deleted infectious salmon anaemia virus (HPR∆ ISAV), Koi herpes virus (KHV), epizootic haematopoietic necrosis virus (EHNV), infectious haematopoietic necrosis virus (IHNV) or viral haemorrhagic septicaemia virus (VHSV) were detected, in the field or during experiments, were classified as reservoir species with different levels of certainty depending on the diagnostic tests used. Where experimental evidence indicated transmission of the pathogen from a studied species to another known susceptible species, the studied species was classified as a vector species. Although the quantification of the risk of spread of the pathogens by the vectors or reservoir species was not part of the terms or reference, such risks do exist for the vector species, since transmission from infected vector species to susceptible species was proven. Where evidence for transmission from infected fish was not found, these were defined as reservoirs. Nonetheless, the risk of the spread of the pathogens from infected reservoir species cannot be excluded. Evidence identifying conditions that may prevent transmission by vectors or reservoir fish species during transport was collected from scientific literature. For VHSV, IHNV or HPR∆ ISAV, it was concluded that under transport conditions at temperatures below 25°C, it is likely (66–90%) they will remain infective. Therefore, vector or reservoir species that may have been exposed to these pathogens in an affected area in the wild, aquaculture establishments or through water supply can possibly transmit VHSV, IHNV or HPR∆ ISAV into a non-affected area when transported at a temperature below 25°C. The conclusion was the same for EHN and KHV; however, they are like

Crassostrea gigas oysters represent a significant global food source,with 4.7 million tons harvested per year. In 2001, the bacteriumVibrioaestuarianus francensisemerged as a pathogen that causes adult oyster mortality in France and Ireland. Its impact on oyster aquaculture has increased in Europe since its reemergence in 2012. To better understand the evolutionary mechanisms leading to the emergence and persistence over time of this pathogen, we conducted a survey of mollusk diseases through national reference laboratories (NRLs) across Europe. We analyzed54 new genomes of Vibrio aestuarianus(Va) isolated from multiple environmental compartments since 2001, in areas with and withoutbivalve mortalities. We used a combination of comparative genomics and population genetics approaches and show thatVa has a classical epidemic population structure from which the pathogenic Va francensis subspecies emerged and clonally expanded.Furthermore, we identified a specific cus-cop-containing island conferring copper resistance to Va francensiswhose acquisition may have favored the emergence of pathogenic lineages adapted and specialized to oysters.

Vector or reservoir species of five mollusc diseases listed in the Animal Health Law were identified, based on evidence generated through an extensive literature review, to support a possible updating of Regulation (EU) 2018/1882. Mollusc species on or in which Mikrocytos mackini, Perkinsus marinus, Bonamia exitiosa, Bonamia ostreae and Marteilia refringens were detected, in the field or during experiments, were classified as reservoir species with different levels of certainty depending on the diagnostic tests used. Where experimental evidence indicated transmission of the pathogen from a studied species to another known susceptible species, this studied species was classified as a vector species. Although the quantification of the risk of spread of the pathogens by the vectors or reservoir species was not part of the terms of reference, such risks do exist for the vector species, since transmission from infected vector species to susceptible species was proven. Where evidence for transmission from infected molluscs was not found, these were defined as reservoir. Nonetheless, the risk of the spread of the pathogens from infected reservoir species cannot be excluded. Evidence identifying conditions that may prevent transmission by vectors or reservoir mollusc species during transport was collected from scientific literature. It was concluded that it is very likely to almost certain (90–100%) that M. mackini, P. marinus, B. exitiosa B. ostreae and M. refringens will remain infective at any possible transport condition. Therefore, vector or reservoir species that may have been exposed to these pathogens in an affected area in the wild or at aquaculture establishments or through contaminated water supply can possibly transmit these pathogens. For transmission of M. refringens, the presence of an intermediate host, a copepod, is necessary.

On request of the EU Commission, EFSA carried out an Extensive Literature Review (ELR) to provide a list of vector species or reservoirs species of pathogens of crustaceans, listed in Annex II to the AHL, aiming to update the Annex of Implementing Regulation (EU) 2018/1882. In this Technical Report, the detailed review protocol of the ELR and assessment of potential vector and reservoir species is described of the crustacean pathogens listed in Annex II to the AHL: Taura syndrome virus (TSV), Yellow head virus (YHV) or White spot syndrome virus (WSSV). In total 2,530 research publications were collected for abstract screening and from these, 110 were selected for further full text analysis. In the final data collection and assessment 34 relevant research publications were used for extracting information on vector and reservoir species of the above crustacean pathogens. The results for crustacean species for which scientific evidence indicates that a role as vector species or reservoir species is likely are presented as tables in the supplementary material of this report.

Vector or reservoir species of five fish diseases listed in the Animal Health Law were identified, based on evidence generated through an extensive literature review (ELR), to support a possible updating of Regulation (EU) 2018/1882. Fish species on or in which highly polymorphic region-deleted infectious salmon anaemia virus (HPR∆ ISAV), Koi herpes virus (KHV), epizootic haematopoietic necrosis virus (EHNV), infectious haematopoietic necrosis virus (IHNV) or viral haemorrhagic septicaemia virus (VHSV) were detected, in the field or during experiments, were classified as reservoir species with different levels of certainty depending on the diagnostic tests used. Where experimental evidence indicated transmission of the pathogen from a studied species to another known susceptible species, the studied species was classified as a vector species. Although the quantification of the risk of spread of the pathogens by the vectors or reservoir species was not part of the terms or reference, such risks do exist for the vector species, since transmission from infected vector species to susceptible species was proven. Where evidence for transmission from infected fish was not found, these were defined as reservoirs. Nonetheless, the risk of the spread of the pathogens from infected reservoir species cannot be excluded. Evidence identifying conditions that may prevent transmission by vectors or reservoir fish species during transport was collected from scientific literature. For VHSV, IHNV or HPR∆ ISAV, it was concluded that under transport conditions at temperatures below 25°C, it is likely (66–90%) they will remain infective. Therefore, vector or reservoir species that may have been exposed to these pathogens in an affected area in the wild, aquaculture establishments or through water supply can possibly transmit VHSV, IHNV or HPR∆ ISAV into a non-affected area when transported at a temperature below 25°C. The conclusion was the same for EHN and KHV; however, they are likely

Vector or reservoir species of three diseases of crustaceans listed in the Animal Health Law were identified based on evidence generated through an extensive literature review, to support a possible updating of Regulation (EU) 2018/1882. Crustacean species on or in which Taura syndrome virus (TSV), Yellow head virus (YHV) or White spot syndrome virus (WSSV) were identified, in the field or during experiments, were classified as reservoir species with different levels of certainty depending on the diagnostic tests used. Where experimental evidence indicated transmission of the pathogen from a studied species to another known susceptible species, the studied species was classified as vector species. Although the quantification of the risk of spread of the pathogens by the vectors or reservoir species was not part of the terms of reference, such risks do exist for the vector species, since transmission from infected vector species to susceptible species was proven. Where evidence for transmission from infected crustaceans was not found, these were defined as reservoirs. Nonetheless, the risk of the spread of the pathogens from infected reservoir species cannot be excluded. Evidence identifying conditions that may prevent transmission by vectors during transport was collected from scientific literature. It was concluded that it is very likely to almost certain (90–100%) that WSSV, TSV and YHV will remain infective at any possible transport condition. Therefore, vector or reservoir species that may have been exposed to these pathogens in an affected area in the wild or aquaculture establishments or by water supply can possibly transmit WSSV, TSV and YHV.

On request of the EU Commission, EFSA carried out an Extensive Literature Review (ELR) to provide a list of vector species or reservoirs species of pathogens of crustaceans, listed in Annex II to the AHL, aiming to update the Annex of Implementing Regulation (EU) 2018/1882. In this Technical Report, the detailed review protocol of the ELR and assessment of potential vector and reservoir species is described of the crustacean pathogens listed in Annex II to the AHL: Taura syndrome virus (TSV), Yellow head virus (YHV) or White spot syndrome virus (WSSV). In total 2,530 research publications were collected for abstract screening and from these, 110 were selected for further full text analysis. In the final data collection and assessment 34 relevant research publications were used for extracting information on vector and reservoir species of the above crustacean pathogens. The results for crustacean species for which scientific evidence indicates that a role as vector species or reservoir species is likely are presented as tables in the supplementary material of this report.

Vector or reservoir species of three diseases of crustaceans listed in the Animal Health Law were identified based on evidence generated through an extensive literature review, to support a possible updating of Regulation (EU) 2018/1882. Crustacean species on or in which Taura syndrome virus (TSV), Yellow head virus (YHV) or White spot syndrome virus (WSSV) were identified, in the field or during experiments, were classified as reservoir species with different levels of certainty depending on the diagnostic tests used. Where experimental evidence indicated transmission of the pathogen from a studied species to another known susceptible species, the studied species was classified as vector species. Although the quantification of the risk of spread of the pathogens by the vectors or reservoir species was not part of the terms of reference, such risks do exist for the vector species, since transmission from infected vector species to susceptible species was proven. Where evidence for transmission from infected crustaceans was not found, these were defined as reservoirs. Nonetheless, the risk of the spread of the pathogens from infected reservoir species cannot be excluded. Evidence identifying conditions that may prevent transmission by vectors during transport was collected from scientific literature. It was concluded that it is very likely to almost certain (90?100%) that WSSV, TSV and YHV will remain infective at any possible transport condition. Therefore, vector or reservoir species that may have been exposed to these pathogens in an affected area in the wild or aquaculture establishments or by water supply can possibly transmit WSSV, TSV and YHV.

Vector or reservoir species of five fish diseases listed in the Animal Health Law were identified, based on evidence generated through an extensive literature review (ELR), to support a possible updating of Regulation (EU) 2018/1882. Fish species on or in which highly polymorphic region-deleted infectious salmon anaemia virus (HPR? ISAV), Koi herpes virus (KHV), epizootic haematopoietic necrosis virus (EHNV), infectious haematopoietic necrosis virus (IHNV) or viral haemorrhagic septicaemia virus (VHSV) were detected, in the field or during experiments, were classified as reservoir species with different levels of certainty depending on the diagnostic tests used. Where experimental evidence indicated transmission of the pathogen from a studied species to another known susceptible species, the studied species was classified as a vector species. Although the quantification of the risk of spread of the pathogens by the vectors or reservoir species was not part of the terms or reference, such risks do exist for the vector species, since transmission from infected vector species to susceptible species was proven. Where evidence for transmission from infected fish was not found, these were defined as reservoirs. Nonetheless, the risk of the spread of the pathogens from infected reservoir species cannot be excluded. Evidence identifying conditions that may prevent transmission by vectors or reservoir fish species during transport was collected from scientific literature. For VHSV, IHNV or HPR? ISAV, it was concluded that under transport conditions at temperatures below 25°C, it is likely (66?90%) they will remain infective. Therefore, vector or reservoir species that may have been exposed to these pathogens in an affected area in the wild, aquaculture establishments or through water supply can possibly transmit VHSV, IHNV or HPR? ISAV into a non-affected area when transported at a temperature below 25°C. The conclusion was the same for EHN and KHV; however, they are likely

Vector or reservoir species of five mollusc diseases listed in the Animal Health Law were identified, based on evidence generated through an extensive literature review, to support a possible updating of Regulation (EU) 2018/1882. Mollusc species on or in which Mikrocytos mackini, Perkinsus marinus, Bonamia exitiosa, Bonamia ostreae and Marteilia refringens were detected, in the field or during experiments, were classified as reservoir species with different levels of certainty depending on the diagnostic tests used. Where experimental evidence indicated transmission of the pathogen from a studied species to another known susceptible species, this studied species was classified as a vector species. Although the quantification of the risk of spread of the pathogens by the vectors or reservoir species was not part of the terms of reference, such risks do exist for the vector species, since transmission from infected vector species to susceptible species was proven. Where evidence for transmission from infected molluscs was not found, these were defined as reservoir. Nonetheless, the risk of the spread of the pathogens from infected reservoir species cannot be excluded. Evidence identifying conditions that may prevent transmission by vectors or reservoir mollusc species during transport was collected from scientific literature. It was concluded that it is very likely to almost certain (90?100%) that M.?mackini, P.?marinus, B.?exitiosa B.?ostreae and M.?refringens will remain infective at any possible transport condition. Therefore, vector or reservoir species that may have been exposed to these pathogens in an affected area in the wild or at aquaculture establishments or through contaminated water supply can possibly transmit these pathogens. For transmission of M.?refringens, the presence of an intermediate host, a copepod, is necessary.

[Introduction] The separate species status of the paramyxid parasitic protists Marteilia refringens and Marteilia pararefringens has been a topic of debate for the past two decades. The two parasites were originally classified as distinct species before being 46ynonymized into a single species comprising two ‘types’: M. refringens M-type and O-type. The two types were redesignated as distinct species (M. refringens and M. pararefringens) in 2018 based on consistent differences in longer regions of ribosomal RNA (rRNA) array sequences, but from only a limited number of samples. [Methodology] Here we generate full rRNA arrays using long-range PCR and next generation sequencing (NGS) from a larger number of M. refringens and M. pararefringens infections spanning the geographical range of their distribution to (1) reinforce evidence that M. refringens and M. pararefringens are genetically distinct species, (2) demonstrate consistent differences within the current diagnostic regions and (3) determine whether newly revealed variable regions outside of the current diagnostic regions could be used as complementary informative marker regions. [Results] Phylogenetic analysis of the transcribed region of rRNA arrays (ETS-18S-ITS1-5.8S-TS2-28S) provides maximal support for, and separation of M. refringens and M. pararefringens across investigated geographical ranges. Phylogenetic analysis of the most variable regions of the array also supported the two separate Marteilia species. [Conclusions] Robust marker regions that delimit M. refringens and M. pararefringens as two separate species will allow the two parasites to be studied independently from one another to investigate the host preference, pathogenicity, and lifecycle of each parasite

The flat oyster Ostrea edulis is an oyster species native to Europe. It has declined to functional extinction in many areas of the NE Atlantic for several decades. Factors explaining this decline include over-exploitation of natural populations and diseases like bonamiosis, regulated across both the EU and the wider world and caused by the intracellular protozoan parasite Bonamia ostreae. To date, very limited sequence data are available for this Haplosporidian species. We present here the first transcriptome of B. ostreae. As this protozoan is not yet culturable, it remains extremely challenging to obtain high-quality -omic data. Thanks to a specific parasite isolation protocol and a dedicated bioinformatic pipeline, we were able to obtain a high-quality transcriptome for an intracellular marine micro-eukaryote, which will be very helpful to better understand its biology and to consider the development of new relevant diagnostic tools.

Outside-host parasite survival is a key parameter to better understand disease mechanisms, especially for marine pathogens transmitted from one host to another through an environmental stage. For non-cultivable micro-parasites like Marteilia refringens, a protozoan parasite infecting the flat oyster Ostrea edulis, investigating this parameter requires innovative approaches. In the present study, we have developed an Environmental DNA (eDNA)-based method allowing detecting and quantifying up to 25 and 10 parasites DNA in seawater and sediment, respectively. This method was used in combination with light and transmission electron microscopy (TEM) to study experimentally parasite survival in seawater and flat oyster faeces after its release from naturally infected oysters. M. refringens DNA could be detected up to 20 days, in both seawater and oyster faeces with a more stable detection over time in the latter. Light and transmission microscopy confirm that parasites leaving flat oysters are sporangia. We also observed a membrane dissolution of the sporangia over time that could indicate the release of parasite spore. This study not only improves our understanding of M. refringens ecology but also highlights the interest to combine molecular and microscopical analysis to study non-cultivable micro-parasites life cycle outside their host.

Mortality outbreaks of young Pacific oysters, Crassostrea gigas, have seriously affected the oyster-farming economy in several countries around the world. Although the causes of these mortality outbreaks appear complex, a viral agent has been identified as the main factor: a herpesvirus called ostreid herpesvirus 1 (OsHV-1). Autophagy is an important degradation pathway involved in the response to several pathologies including viral diseases. In C. gigas, recent studies indicate that this pathway is conserved and functional in at least haemocytes and the mantle. Furthermore, an experimental infection in combination with compounds known to inhibit or induce autophagy in mammals revealed that autophagy is involved in the response to OsHV-1 infection. In light of these results, the aim of this study was to determine the role of autophagy in the response of the Pacific oyster to infection by virus OsHV-1. For this purpose, an experimental infection in combination with a modulator of autophagy was performed on Pacific oysters known to have intermediate susceptibility to OsHV-1 infection. In haemolymph and the mantle, the autophagy response was monitored by flow cytometry, western blotting, and real-time PCR. At the same time, viral infection was evaluated by quantifying viral DNA and RNA amounts by real-time PCR. Although the results showed activation of autophagy in haemolymph and the mantle 14 hours post infection (after viral replication was initiated), they were also indicative of different regulatory mechanisms of autophagy in the two tissues, thus supporting an important function of autophagy in the response to virus OsHV-1.

The Pacific cupped oyster Crassostrea gigas is one of the most “globalized” marine invertebrates and its production is predominant in many parts of the world including Europe. However, it is threatened by mortality events associated with pathogenic microorganisms such as the virus OsHV-1 and the bacteria Vibrio aestuarianus. C. gigas is also a host for protozoan parasites including haplosporidians. In contrast with Haplosporidium nelsoni previously detected in Europe, H. costale was considered exotic although its presence in French oysters was suggested in the 1980s based on ultrastructural examination. Here, a combination of light and transmission electron microscopy, PCR and sequencing allowed characterizing the presence of the parasite in the context of low mortality events which occurred in 2019 in France. Histological observation revealed the presence of uninucleated, plasmodial and spore stages within the connective tissues of some oysters. Ultrastructural features were similar to H. costale ones in particular the presence of axe-shaped haplosporosomes in spore cytoplasms. Three fragments of the genome including partial small subunit rRNA gene, the ITS-1, 5.8S and ITS-2 array and part of the actin gene were successfully sequenced and grouped with H. costale homologous sequences. This is the first time that the presence of H. costale was confirmed in C. gigas in France. Furthermore, a TaqMan real-time PCR assay was developed and validated (DSe = 92.6% (78.2-99.8) and DSp = 95.5% (92.3-98.6)) to enable the rapid and specific detection of the parasite. The application of the PCR assay on archived samples revealed that the parasite has been present in French oyster populations at least since 2008. Considering the little information available on this parasite, the newly developed TaqMan assay will be very helpful to investigate the temporal and geographic distribution and the life cycle of the parasite in France and more generally in C. gigas geographic range.

Pathogen surveillance and diagnostic methods are constantly evolving. Sequencing can provide critical information to diagnose diseases and inform control and mitigation strategies by identifying genetically distinct pathogen variants that may have different host reservoir species or geographic distributions. However, most reference laboratories for marine mollusc diseases lack the resources or expertise for sequencing and data analysis. We therefore developed a user-friendly web-application, called MoPSeq-DB. MoPSeq-DB, is an open-source tool based on the Python web-framework Django. It is deployed through a Docker container, on a dedicated server. Genomes as well as their annotations and variations are stored and organised in a folder architecture designed to make files available to users. Annotation and variation files are parsed and summarised in interactive Javascript graphs using Python and Bash scripts. Then, a pre-built phylogenetic tree, based on all genomes included in the database, can also be visualised and handled. MoPSeq-DB web-platform references curated genomic data related to mollusc pathogens, gives users opportunities to interactively visualise data and provides integrated analysis tools. The database currently primary focuses on the OsHV-1 virus, but will later be completed with other mollusc pathogens such as the bacterium Vibrio aestuarianus or the protozoa Marteilia refringens. This project will provide robust bases to unify all sequence-based work related to mollusc pathogens and will offer unprecedented opportunities to carry out monitoring and diagnosis in near-real time. MoPSeq-DB is, to our knowledge, the first comparative genome browser dedicated to mollusc pathogens. It automates commonly used bioinformatics workflows, enabling convenient and fast data exploration, particularly for non-bioinformaticians, in an intuitive and user-friendly way. It has minimal hardware requirements and is easy to install, host, and update. MoPSeq-DB folder