Characterization of actin genes in Bonamia ostreae and their application to phylogeny of the Haplosporidia

Bonamia ostreae is a protozoan parasite that infects the European flat oyster Ostrea edulis, causing systemic infections and resulting in massive mortalities in populations of this valuable bivalve species. In this work, we have characterized B. ostreae actin genes and used their sequences for a phylogenetic analysis. Design of different primer sets was necessary to amplify the central coding region of actin genes of B. ostreae. Characterization of the sequences and their amplification in different samples demonstrated the presence of 2 intragenomic actin genes in B. ostreae, without any intron. The phylogenetic analysis placed B. ostreae in a clade with Minchinia tapetis, Minchinia teredinis and Haplosporidium costale as its closest relatives, and demonstrated that the paralogous actin genes found in Bonamia resulted from a duplication of the original actin gene after the Bonamia origi

Managing marine mollusc diseases in the context of regional and international commerce: policy issues and emerging concerns

Marine mollusc production contributes to food and economic security worldwide and provides valuable ecological services, yet diseases threaten these industries and wild populations. Although the infrastructure for mollusc aquaculture health management is well characterized, its foundations are not without flaws. Use of notifiable pathogen lists can leave blind spots with regard to detection of unlisted and emerging pathogens. Increased reliance on molecular tools has come without similar attention to diagnostic validation, raising questions about assay performance, and has been accompanied by a reduced emphasis on microscopic diagnostic expertise that could weaken pathogen detection capabilities. Persistent questions concerning pathogen biology and ecology promote regulatory paralysis that impedes trade and which could weaken biosecurity by driving commerce to surreptitious channels. Solutions that might be pursued to improve shellfish aquaculture health management include the establishment of more broad-based surveillance programmes, wider training and use of general methods like histopathology to ensure alertness to emerging diseases, an increased focus on assay assessment and validation as fundamental to assay development, investment in basic research, and application of risk analyses to improve regulation. A continual sharpening of diagnostic tools and approaches and deepening of scientific knowledge is necessary to manage diseases and promote sustainable molluscan shellfish industries

A herpes-like virus infects a non-ostreid bivalve species: virus replication in Ruditapes philippinarum larvae

Sporadic high mortalities were reported in June 1997 among hatchery-reared larval Manila clam Ruditapes philippinarum in a French commercial hatchery. Cellular abnormalities were observed in semi-thin sections in affected animals. Transmission electron microscopy revealed the presence of herpes-like virus particles in larvae. This is the first description of a herpes-like virus infection in larval R. philippinarum, a non-ostreid bivalve species. Virus particles were similar to other herpes-like viruses described from different oyster species with respect to ultrastructure and morphogenesis. Electron microscopic examination also demonstrated cells with condensed chromatin and extensive perinuclear fragmentation of chromatin. Like viruses infecting oysters, the herpes-like virus detected in clams may induce apoptosis in infected animals

Perspectives of diagnostic approaches for mollusc diseases

Surveillance of mollusc diseases is routinely performed by histology and PGR. Efforts made in re-search and development of DNA-based diagnostic methods currently offer a broad panel of probes and tests. TTiese methods have the theoretical advantages of high sensitivity and high specificity and possible rapid screening of molluscs for the presence of a targeted pathogen. However, validation and standardisation of these tests are still needed. In recent years, the European Union Reference Laboratory (EURL) for mollusc diseases has developed and validated a range of duplex Taqman\uae PCR assays aiming at facilitating the detection of bivalve pathogens notifiable to the EU. These assays offer good performances and allow better monitoring and investigation of the epidemiol\uacogy of these different pathogens. Complementary to these PCR assays, new diagnostic approaches based on the use of passive sensors, Magnetic Beads (MBs), electrochemical biosensors, MALDI-TOF MS or Next Generation Sequencing (NGS) have been developed and tested notably in the context of the European project H2020 VIVALDI. The interest of these tools to better detect, characterise and monitor known pathogens is presented and discussed. These new developments will require further assessment, standardisation and validation before being available for routine diagnostics. Additionally, they will certainly not replace but rather complement diagnostic tools currently used to ensure alertness to emerging diseases

New evidence for the involvement of Paracartia grani (Copepoda, Calanoida) in the life cycle of Marteilia refringens (Paramyxea)

The dynamics of the protozoan parasite Marteilia refringens was studied in Thau lagoon, an important French shellfish site, for 1 year in three potential hosts: the Mediterranean mussel Mytilus galloprovincialis (Mytiliidae) the grooved carpet shell Ruditapes decussatus (Veneriidae) and the copepod Paracartia grani (Acartiidae). Parasite DNA was detected by PCR in R. decussatus. In situ hybridisation showed necrotic cells of M. refringens in the digestive epithelia of some R. decussatus suggesting the non-involvement of this species in the parasite life cycle. In contrast, the detection of M. refringens in mussels using PCR appeared bimodal with two peaks in spring and autumn. Histological observations of PCR-positive mussels revealed the presence of different parasite stages including mature sporangia in spring and autumn. These results suggest that the parasite has two cycles per year in the Thau lagoon and that mussels release parasites into the water column during these two periods. Moreover, PCR detection of the parasite in the copepodid stages of P. grani between June and November supports the hypothesis of the transmission of the parasite from mussels to copepods and conversely. In situ hybridisation performed on copepodites showed labeling in some sections. Unusual M. refringens cells were observed in the digestive tract and the gonad from the third copepodid stage, suggesting that the parasite could infect a copepod by ingestion and be released through the gonad. This hypothesis is supported by the PCR detection of parasite DNA in copepod eggs from PCR-positive females, which suggests that eggs could contribute to the parasite spreading in the water and could allow overwintering of M. refringens. Finally, in order to understand the interactions between mussels and copepods, mussel retention efficiency (number of copepods retained by a mussel) was measured for all P. grani developmental stages. Results showed that all copepod stages could contribute to the transmission of the parasite, especially eggs and nauplii which were retained by up to 90%