The mortality of juvenile hollow oysters has been rising sharply since 2008 and now affects all continents. France and the Thau lagoon are no exception, with mortality rates of up to 80%. Two main pathogens have been found in the dead animals: the OsHV-1 virus (herpes virus) and bacteria of the Vibrio genus. The diseases they cause are linked to environmental factors and occur at different stages of growth (juvenile and adult oysters). Juvenile oysters can succumb to fulminant septicemia within 72 hours. 

In order to support oyster farmers in their adaptation strategies, the Syndicat Mixte du Bassin de Thau (SMBT) has requested the expertise of I.A.G.E to initiate an R&D project aimed at developing a rapid detection test for the main pathogens affecting hollow oysters. Eventually, this detection test could lead to an alert or early warning system.
In order to rapidly and reliably detect the presence of the main known pathogens, a multi-target method was designed with specific probes developed to quantify pathogenic species within Vibrio genus (V.  aestuarianus, V. splendidus, V.  crassostrea and V.  tasmaniensis) and the Ostreid Herpesvirus-1 (OsHV-1). An extraction method was developed to analyze oyster samples, and water samples were analyzed with the patented process developed by I.A.GE for wastewater monitoring of COVID-19 (B380612PCT).

Samples were taken at three sites in the Thau lagoon. They were carried out every week for one year on spat oysters, on adult oysters and in the water nearby. Grab vs .24 h sampling of water were evaluated with the water sampler developed by I.A.G.E for wastewater monitoring of COVID-19.

The first conclusions show that I.A.G.E can detect and quantify the different pathogens in water and oysters. They were able to confirm the sensitivity of different oyster species. A correlation was also shown between the water measurements and the monthly mortalities observed. This project confirms the potential of dPCR in the development of diagnostic & early warning methods.