Understanding the role of Francisella halioticida in mussel mortalities in France: an integrative approach

Understanding the role of Francisella halioticida in mussel mortalities in France: an integrative approach

Since 2014, mass mortalities of mussels Mytilus spp. have occurred in production areas on the Atlantic coast of France. The aetiology of these outbreaks remained unknown until the bacterium Francisella halioticida was detected in some mussel mortality cases. This retrospective study was conducted to...

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Bibliographic Details
Published in:Diseases of aquatic organisms Vol. 158; pp. 81 - 99
Main Authors: Garcia, Céline, Charles, Maud, Chollet, Bruno, Nadeau, Aurélie, Serpin, Delphine, Quintric, Laure, Pépin, Jean-François, Houssin, Maryline, Lupo, Coralie
Format: Journal Article
Language:English
Published: Germany Inter-Research Science Center 25-04-2024
Inter Research
Subjects:
Animals
Bacteria
DNA barcoding
Factor analysis
France - epidemiology
Francisella - classification
Francisella - genetics
Francisella - isolation & purification
Francisella halioticida
Life Sciences
Mollusks
Mortality
Mussels
Mytilus - microbiology
Necrosis
Polymerase chain reaction
Real time
Retrospective Studies
Risk analysis
Risk factors
RNA, Ribosomal, 16S - genetics
rRNA 16S
Sciences of the Universe
France
Causal inference
16S rRNA metabarcoding
Mussel mortality
Real-time PCR
Molecular epidemiology
Histology
Francisella halioticida
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Summary:Since 2014, mass mortalities of mussels Mytilus spp. have occurred in production areas on the Atlantic coast of France. The aetiology of these outbreaks remained unknown until the bacterium Francisella halioticida was detected in some mussel mortality cases. This retrospective study was conducted to assess the association between F. halioticida and these mussel mortalities. Mussel batches (n = 45) from the Atlantic coast and English Channel were selected from archived individual samples (n = 863) collected either during or outside of mortality events between 2014 and 2017. All mussels were analysed by real-time PCR assays targeting F. halioticida; in addition, 185 were analysed using histological analysis and 178 by 16S rRNA metabarcoding. F. halioticida DNA was detected by real-time PCR and 16S rRNA metabarcoding in 282 and 34 mussels, respectively. Among these individuals, 82% (real-time PCR analysis) and 76% (16S rRNA metabarcoding analysis) were sampled during a mortality event. Histological analyses showed that moribund individuals had lesions mainly characterized by necrosis, haemocyte infiltration and granulomas. Risk factor analysis showed that mussel batches with more than 20% of PCR-positive individuals were more likely to have been sampled during a mortality event, and positive 16S rRNA metabarcoding batches increased the strength of the association with mortality by 11.6 times. The role of F. halioticida in mussel mortalities was determined by reviewing the available evidence. To this end, a causation criteria grid, tailored to marine diseases and molecular pathogen detection tools, allowed more evidence to be gathered on the causal role of this bacterium in mussel mortalities.
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ISSN:0177-5103
1616-1580
DOI:10.3354/dao03782