Field studies on the effects of Marteilia sp. on growth of mussel Mytilus galloprovincialis in Thermaikos Gulf

Health Status of Mytilus chilensis from Intensive Culture Areas in Chile Assessed by Molecular, Microbiological, and Histological Analyses

Shellfish farming is a relevant economic activity in Chile, where the inner sea in Chiloé island concentrates 99% of the production of the mussel Mytilus chilensis. This area is characterized by the presence of numerous human activities, which could harm the quality of seawater. Additionally, the presence of potentially pathogenic microorganisms can influence the health status of mussels, which must be constantly monitored. To have a clear viewpoint of the health status of M. chilensis and to study its potential as a host species for exotic diseases, microbiological, molecular, and histological analyses were performed. This study was carried out in October 2018, where M. chilensis gut were studied for: presence of food-borne bacteria (Vibrio parahaemolyticus, Escherichia coli, Salmonella spp.), exotic bacteria (“Candidatus Xenohaliotis californiensis”), viruses (abalone and Ostreid herpes virus), and protozoa (Marteilia spp., Perkinsus spp. and Bonamia spp.). Additionally, 18S rDNA metabarcoding and histology analyses were included to have a complete evaluation of the health status of M. chilensis. Overall, despite the presence of risk factors, abnormal mortality rates were not reported during the monitoring period and the histological examination did not reveal significant lesions. Pathogens of mandatory notification to World Organization for Animal Health (OIE) and the Chilean National Fisheries and Aquaculture Service (SERNAPESCA) were not detected, which confirms that M. chilensis have a good health status, highlighting the importance of an integrated vision of different disciplines to ensure the sustainability of this important mussel industry in Chile.

How Safe to Eat Are Raw Bivalves? Host Pathogenic and Public Health Concern Microbes within Mussels, Oysters, and Clams in Greek Markets

Raw-bivalves consumption is a wide trend in Mediterranean countries. Despite the unambiguous nutritional value of seafood, raw consumption of bivalves may involve risks that could pose a significant threat to consumers' health. Their filter-feeding behavior is responsible for the potential hosting of a wide variety of microorganisms, either pathogenic for the bivalves or public health threats. Under this prism, the current study was conducted in an effort to evaluate the risk of eating raw bivalves originating from the two biggest seafood markets in Thessaloniki, the largest production area of bivalves in Greece. Both microbiological and molecular methodologies were applied in order to assess the presence of various harmful microbes, including noroviruses, Bonamia, Marteilia, Esherichia coli, Salmonella, and Vibrio. Results indicated the presence of several Vibrio strains in the analyzed samples, of which the halophilic Vibrio harveyi was verified by 16S rRNA sequencing; other than this, no enteropathogenic Vibrio spp. was detected. Furthermore, although Esherichia coli was detected in several samples, it was mostly below the European Union (EU) legislation thresholds. Interestingly, the non-target Photobacterium damselae was also detected, which is associated with both wound infections in human and aquatic animals. Regarding host pathogenic microorganisms, apart from Vibrio harveyi, the protozoan parasite Marteilia refrigens was identified in oysters, highlighting the continuous infection of this bivalve in Greece. In conclusion, bivalves can be generally characterized as a safe-to-eat raw food, hosting more bivalve pathogenic microbes than those of public health concern.

The current situation and potential effects of climate change on the microbial load of marine bivalves of the Greek coastlines: an integrative review

Global warming affects the aquatic ecosystems, accelerating pathogenic microorganisms' and toxic microalgae's growth and spread in marine habitats, and in bivalve molluscs. New parasite invasions are directly linked to oceanic warming. Consumption of pathogen-infected molluscs impacts human health at different rates, depending, inter alia, on the bacteria taxa. It is therefore necessary to monitor microbiological and chemical contamination of food. Many global cases of poisoning from bivalve consumption can be traced back to Mediterranean regions. This article aims to examine the marine bivalve's infestation rate within the scope of climate change, as well as to evaluate the risk posed by climate change to bivalve welfare and public health. Biological and climatic data literature review was performed from international scientific sources, Greek authorities and State organizations. Focusing on Greek aquaculture and bivalve fisheries, high-risk index pathogenic parasites and microalgae were observed during summer months, particularly in Thermaikos Gulf. Considering the climate models that predict further temperature increases, it seems that marine organisms will be subjected in the long term to higher temperatures. Due to the positive linkage between temperature and microbial load, the marine areas most affected by this phenomenon are characterized as 'high risk' for consumer health.

First detection of the invasive Haplosporidian and Mycobacteria parasites hosting the endangered bivalve Pinna nobilis in Thermaikos Gulf, North Greece

Mycobacterium sp. and Haplosporidium pinnae constitute invasive parasite species of bivalves, reported for the first time in the present study in the Aegean Sea and Thermaikos Gulf, respectively. During the last years, the endangered fan mussel (Pinna nobilis) experienced several mortality events in the Mediterranean Sea that caused deaths to 90% or more of their populations and have been attributed to infections by these pathogens. In Greece, two mass mortality events have been recently reported, namely in the Gulf of Kalloni and in Limnos island. In the present study we investigated the presence of both pathogens in P. nobilis from these marine areas as well as from Thermaikos Gulf using both histopathological microscopy and molecular markers. The detected parasite DNA was further quantified in the three populations utilizing a real time qPCR. Histopathological results indicated the presence of a Mycobacterium species alongside with the existence of the Haplosporidian parasite, which was identified in all mortality events in the Mediterranean Sea. The parasite was present in different phases mostly on the digestive gland epithelium. Phylogenetic analysis confirmed the taxonomy of the Haplosporidian parasite as the recently described Haplosporidium pinnae, whereas it failed to identify the Mycobacteria parasite at species level. While Mycobacterium sp. was detected in all examined specimens, H. pinnae was not detected in all diseased fan mussels. Interestingly, monitoring of P. nobilis population from Thermaikos Gulf, an estuary of extremely high importance for bivalve production, revealed the presence of both pathogens in a few specimens in higher quantity but with no symptoms of the disease. Besides, all the specimens from Thermaikos Gulf had inflammatory responses similarly to moribund specimens from mortality events.