Microbial Diseases of Bivalve Mollusks: Infections, Immunology and Antimicrobial Defense

Abstract

A variety of bivalve mollusks (phylum Mollusca, class Bivalvia) constitute a prominent commodity in fisheries and aquacultures, but are also crucial in order to preserve our ecosystem’s complexity and function. Bivalve mollusks, such as clams, mussels, oysters and scallops, are relevant bred species, and their global farming maintains a high incremental annual growth rate, representing a considerable proportion of the overall fishery activities. Bivalve mollusks are filter feeders; therefore by filtering a great quantity of water, they may bioaccumulate in their tissues a high number of microorganisms that can be considered infectious for humans and higher vertebrates. Moreover, since some pathogens are also able to infect bivalve mollusks, they are a threat for the entire mollusk farming industry. In consideration of the leading role in aquaculture and the growing financial importance of bivalve farming, much interest has been recently devoted to investigate the pathogenesis of infectious diseases of these mollusks in order to be prepared for public health emergencies and to avoid dreadful income losses. Several bacterial and viral pathogens will be described herein. Despite the minor complexity of the organization of the immune system of bivalves, compared to mammalian immune systems, a precise description of the different mechanisms that induce its activation and functioning is still missing. In the present review, a substantial consideration will be devoted in outlining the immune responses of bivalves and their repertoire of immune cells. Finally, we will focus on the description of antimicrobial peptides that have been identified and characterized in bivalve mollusks. Their structural and antimicrobial features are also of great interest for the biotechnology sector as antimicrobial templates to combat the increasing antibiotic-resistance of different pathogenic bacteria that plague the human population all over the world.

Effects of soluble copper and copper oxide nanoparticle exposure on the immune system of mussels, Mytilus galloprovincialis

“…Here, we observed that exposure to either source of copper followed by a 24 h exposure to the pathogenic bacteria Vibrio tubiashii caused a slight, but not significant increase in bacteria proliferation indicating that copper exposure negatively impacts the immune system health preventing bivalve species from effectively fighting off infection. Some pathogens found in bivalves can cause illness in humans as well . If concentrations of nanoparticle pollution increase in the environment, there could be a greater risk to humans who consume shellfish products, since pathogenic bacteria are part of the natural environment and weakened mussels would not be able to prevent their accumulation in the tissue.…”

Current trends of antimicrobials used in food animals and aquaculture

“…No treatment, sterilization and filtration of inflow water (Zannella et al, 2017) antimicrobials have played a crucial role in prevention, treatment, and control of animal diseases caused by microorganisms. Due to certain advantages, such as exact targeting of pathogens, wellknown mechanisms of activity and desired stability, antimicrobials have justified their usage in food animals and aquaculture, thus playing a main part in the prevention and treatment of bacterial and parasitic diseases.…”

Managing the risk of Vibrio parahaemolyticus infections associated with oyster consumption: A review

“…The effectiveness of implemented FSMSs to eliminate V. parahaemolyticus or reduce its concentration in oysters remains a challenge because of increasingly complex interactions among foodborne pathogens, food, vehicles, and environmental conditions (Froelich & Noble, 2016; Zannella et al., 2017). Challenges in the food safety management of oysters are also complicated by the dynamic operating environment as well as the increasing and changing consumer demands and expectations (Froelich & Noble, 2016).…”