Histopathological and Molecular Study of Pacific Oyster Tissues Provides Insights into V. aestuarianus Infection Related to Oyster Mortality

Abstract

Consumer preference for healthy and sustainable food products has been steadily increasing in recent years. Bivalve mollusks satisfy these characteristics and have captured ever-increasing market shares. However, the expansion of molluscan culture in worldwide and global trade have favored the spread of pathogens around the world. Combined with environmental changes and intensive production systems this has contributed to the occurrence of mass mortality episodes, thus posing a threat to the production of different species, including the Pacific oyster Crassotrea gigas. In the San Teodoro lagoon, one of the most devoted lagoons to extensive Pacific oyster aquaculture in Sardinia, a mortality outbreak was observed with an estimated 80% final loss of animal production. A study combining cultural, biomolecular and histopathological methods was conducted: (1) to investigate the presence of different Vibrio species and OsHV-1 in selected oyster tissues (digestive gland, gills, and mantle); (2) to quantify Vibrio aestuarianus and to evaluate the severity of hemocyte infiltration in infected tissues; (3) to produce post-amplification data and evaluating ToxR gene as a target for phylogenetic analyses. Results provide new insights into V. aestuarianus infection related to oyster mortality outbreaks and pave the way to the development of tools for oyster management.

Gut Symbiotic Microbial Communities in the IUCN Critically Endangered Pinna nobilis Suffering from Mass Mortalities, Revealed by 16S rRNA Amplicon NGS

“…[43]. V. aestuarianus is an important pathogen responsible for massive mortalities in oyster, Crassostrea gigas in Europe and responsible for a greatly negative impact in farms associate with the culture of this species [10,[44][45][46]. The first case of bivalves infected by V. alginolyticus was described in 1965 [47].…”

Emergence and clonal expansion of Vibrio aestuarianus lineages pathogenic for oysters in Europe

“…francensis ( Va francensis ), affecting Crassostrea gigas , the most grown oysters worldwide (93% of the global oyster production) is of particular interest. Indeed, Va francensis has caused recurrent mortality of cultivated adult oysters since 2001 (Garnier et al, 2008), first in France, then in several European countries (France, Italy, Ireland, and Spain; Lasa et al, 2019; Mandas et al, 2020). This spread of Va francensis has resulted in mortality rates of approximately 25% and is a major economic concern as it impacts market‐size oysters (Dégremont et al, 2020).…”

Emergence and clonal expansion of Vibrio aestuarianus lineages pathogenic for oysters in Europe

“…Mortality rates of approximately 25% (18) have had an important economic impact, as they affect market-size oysters. Having previously been restricted to France, this disease has now spread across European countries (France, Italy, Ireland, and Spain) (19, 20). Strains of another V. aestuarianus subspecies (subsp.…”

“…francensis ( Va francensis ) has caused recurrent mortality of adult oysters since 2001 (11). Having previously been restricted to France, this disease has now spread across European countries (France, Italy, Ireland, and Spain) (12, 13). This spread of Va francensis has resulted in mortality rates of approximately 25% and is a major economic concern as it impacts market-size oysters (14).…”