Shellfish as reservoirs of bacterial pathogens

Abstract

Shellfish comprises a variety of animals including bivalves – oysters, clams, quahogs, scallops, mussels, and others including crustaceans – lobsters, crabs, and shrimps. Shellfish naturally found in Grenada, an island nation in the Caribbean, include: blue land crabs (Cardisoma guanhumi), clams (Mercenaria mercenaria), oysters (Isognomon isognomon), queen conchs, also called “lambi” (Strombus gigas), and whelks (West Indian top shell) (Cittarium pica), all of which are used for human consumption in this country. Bacteria are ubiquitous in the marine environment. Shellfish can be a source of commensal bacteria that can be pathogenic to shellfish, as well as those pathogenic to humans. Raw and partially cooked molluscan shellfish (clams, oysters, and mussels) have a long history as vectors of infectious agents[1]. According to Potasman et al.[2], the earliest reports of shellfish-transmitted diseases were documented in the late 19th and early 20th century. Apart from typhoid fever, the most notable examples include Vibrio species, which account for 20% of all outbreaks of shellfishassociated human disease. Other bacteria are Salmonella species, Shigella species, Plesiomonas shigelloides, and Listeria species[2]. Several Vibrio species native to both marine and estuarine environments, have been identified as the causative agents of shellfish-associated human illnesses. These include Vibrio parahaemolyticus (V. parahaemolyticus), Vibrio vulnificus (V. vulnificus), Vibrio cholerae non-O1, Vibrio cholerae, Vibrio cholerae O1, Vibrio fluvialis (V. fluvialis), Vibrio hollisae, Vibrio mimicus, Vibrio alginolyticus (V. alginolyticus), and unidentified or miscellaneous Vibrio species. Among these, all except V. vulnificus, are associated with gastroenteritis of varying severity[1]. Oysterassociated V. vulnificus septicemia and death were first reported in 1975[3]. Another bacterium of public health concern is Salmonella. Compared to vibrios, there have been much less studies on Salmonella in various shellfish. Setti et al.[4] studied the dynamics of Salmonella contamination in the coastal areas of Agadir, a populous region of Southern Morocco where shellfish production is important to the local economy. Salmonella enterica (S. enterica) serovar Kentucky was found almost exclusively in mussels, whereas Salmonella blockley was found in mussels and sediment samples. Identification of Salmonella to serovar level is required ARTICLE INFO ABSTRACT