Abstract
Vibrio aestuarianus is a bacterium related to mortality outbreaks in Pacific oysters, Crassostrea gigas, in France, Ireland, and Scotland since 2011. Knowledge about its transmission dynamics is still lacking, impairing guidance to prevent and control the related disease spread. Mathematical modeling is a relevant approach to better understand the determinants of a disease and predict its dynamics in imperfectly observed pathosystems. We developed here the first marine epidemiological model to estimate the key parameters of V. aestuarianus infection at a local scale in a small and closed oyster population under controlled laboratory conditions. Using a compartmental model accounting for free-living bacteria in seawater, we predicted the infection dynamics using dedicated and model-driven collected laboratory experimental transmission data. We estimated parameters and showed that waterborne transmission of V. aestuarianus is possible under experimental conditions, with a basic reproduction number R0 of 2.88 (95% CI: 1.86; 3.35), and a generation time of 5.5 days. Our results highlighted a bacterial dose–dependent transmission of vibriosis at local scale. Global sensitivity analyses indicated that the bacteria shedding rate, the concentration of bacteria in seawater that yields a 50% chance of catching the infection, and the initial bacterial exposure dose W0 were three critical parameters explaining most of the variation in the selected model outputs related to disease spread, i.e., R0, the maximum prevalence, oyster survival curve, and bacteria concentration in seawater. Prevention and control should target the exposure of oysters to bacterial concentration in seawater. This combined laboratory–modeling approach enabled us to maximize the use of information obtained through experiments. The identified key epidemiological parameters should be better refined by further dedicated laboratory experiments. These results revealed the importance of multidisciplinary approaches to gain consistent insights into the marine epidemiology of oyster diseases.
Highlights
Mass mortality of adult Pacific oysters, Crassostrea gigas, has been reported since 2001 in France, in association with the detection of the bacterium Vibrio aestuarianus
The bacterium V. aestuarianus remained in seawater for 2 days on average
Our model showed that the bacteria shedding rate, the half-infective dose and the initial bacterial exposure dose have a major influence on the outputs related to the extent of infection by V. aestuarianus at a small population scale
Summary
Mass mortality of adult Pacific oysters, Crassostrea gigas, has been reported since 2001 in France, in association with the detection of the bacterium Vibrio aestuarianus. Since 2011, an increase in the incidence of these mortality events has been observed [1] This bacterium has been isolated recently during oyster mortality events in Ireland and Scotland [2, 3]. Such an increase in mortality has a strong direct economic impact, causing considerable concerns among farmers because adult oysters that have reached their marketable size are mainly affected [4]. Oyster mortality rates increase with the bacterial concentration in seawater, indicating a dose-dependent process in disease progression [12]. Because DNA of V. aestuarianus has not been detected in surviving challenged oysters [12], it seems that these oysters never got infected. The quantification of the transmission of these bacteria is a worthwhile step for further elucidating the disease spread and establishment in oyster populations, and to substantially inform disease management
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
