The complex interactions of Ostreid herpesvirus 1, Vibrio bacteria, environment and host factors in mass mortality outbreaks of Crassostrea gigas

Abstract

From the first detection in the Eastern oysters (Crassostrea virginica) in 1972, herpes-like viruses/herpesviruses have been identified in at least 20 bivalve species and have caused massive mortalities in six cultured species of bivalves. Among them, the Pacific oyster (Crassostrea gigas) is most threatened by massive mortalities associated with detection of Ostreid herpesvirus 1 (OsHV-1) and its variants. These mortality events have been reported in more than 12 countries, and OsHV-1 itself has been reported in 15 countries worldwide. Traditionally, the genotype OsHV-1 (or OsHV-1 Var) is the main contributor to bivalve mortalities, but the emergence of variants (e.g. OsHV-1 lVar and related ones, acute viral necrosis virus-AVNV, OsHV-1-SB) is now responsible for new mortality outbreaks in Pacific oysters and other bivalve species. In addition to OsHV-1, Vibrio bacteria and other abiotic and host factors also significantly contribute to mortality outbreaks. To this end, the current contribution aims to synthesize the body of literature on our current knowledge of these mass mortality events to provide insights into the role of each risk factor and complex interactions in the disease process. Specifically, this review encompasses our current knowledge and critical gaps. Important suggestions for future investigation are also presented. Figure 1 Classification of main Pacific oyster (Crassostrea gigas) producing countries in 2016 in tonnes (data taken from FAO FishStatJ, version 3.01.0). The map was generated using http://mapchart.net. Asterisks (*) indicate countries with mass mortality events. ( ) >300 000 tonnes; ( ) >100 000 tonnes; ( ) >10 000 tonnes; ( ) >1000 tonnes; ( ) <1000 tonnes.

Dynamics of the Pacific oyster pathobiota during mortality episodes in Europe assessed by 16S rRNA gene profiling and a new target enrichment next‐generation sequencing strategy

“…Diseases affecting the Pacific oyster ( Crassostrea gigas ) have been rising over the past decades, representing a significant threat for commercial exploitation of both farmed and natural stocks (Alfaro et al ., ). In Europe, mass mortality episodes of C .…”

“…Diseases affecting the Pacific oyster (Crassostrea gigas) have been rising over the past decades, representing a significant threat for commercial exploitation of both farmed and natural stocks (Alfaro et al, 2018). In Europe, mass mortality episodes of C. gigas in farming areas are attributed to complex interactions among oysters, microbial pathogens and environmental variables (Pernet et al, 2012).…”

Oysters as sentinels of climate variability and climate change in coastal ecosystems

“…Among marine life, invertebrates and especially filter feeders like oysters are key species in coastal ecosystems due to the various ecological services they provide (building reef habitats, trophic resource and benthic-pelagic coupling), and due to their economic and societal value through fishing and aquaculture. The Pacific oyster, Crassostrea gigas, which is currently widespread worldwide (Miossec et al 2009), is the main farmed species of oyster with 3.5 10 6 tons globally produced in 2014 (Alfaro et al 2018). In Europe, C. gigas was introduced along the Atlantic coast in the late 1960s for shellfish aquaculture purposes (Humphreys et al 2014).…”

Omics approaches to investigate host–pathogen interactions in mass mortality outbreaks of Crassostrea gigas

“…Massive Pacific oyster mortalities were first reported in the coast of Japan in 1945 (Koganezawa ), and have been observed in 12 countries within all continents, except Antarctica (reviewed by Alfaro et al . ). It is generally agreed that these mortalities are caused mostly by complex interaction among the hosts, pathogens (e.g.…”

“…OsHV‐1 and Vibrio species) and environmental conditions, such as high seawater temperatures (Samain & Mccombie ; Alfaro et al . ; OIE ). The C. gigas mortality events have been reported during summer months (OIE ), and they are often known as ‘summer mortalities’.…”