MEMBRANE TO PROTECT SHELLFISH PRODUCTION TOWARD OSTREID HERPES VIRUS
Ostreid herpes virus, OsHV-1, responsible of mass mortalities of oyster juveniles is a threat for shellfish culture. In this context means of treatment of hatcheries/nurseries have to treat inlet waters are necessary to protect oysters. The aim of the study was to test membrane filtration to eliminate OsHV-1 at the lab scale .
Ultrafiltration membranes in PES with a pore size of 0.02 µm were used to treat contaminated solutions prepared by injection of viral suspensions in oyster spats. To evaluate the retention performance of the process, in vitro and in vivo tests were carried out. In vitro evaluation was realized by virus concentration measurements in water before and after treatment using PCR analysis. In vivo tests consisted in putting in contact ultrafiltered solution with juveniles or larvae (aged 8 days) to simulate real conditions of shellfish production and injecting permeate in juveniles. Oyster mortality was then followed for 7 days and compared to the ones obtained in positive (contaminated seawater) and negative (ultrafiltered seawater) controls.
In vitro measurements highlight a retention of the virus by ultrafiltration process (Figure 1). Indeed, if the retention is not complete because DNA is detected in permeate, its concentration is bellow quantification limit of PCR analysis (10 DNA copy.µL-1) and the removal was up to 4 log. For the 3 tests realized, whatever the quantity of virus in contaminated seawater, the concentration permeate was bellow this limit. In vivo tests are essential to determine the treatment efficiency. In the case of larvae (Figure 2), the test led to a total mortality of oyster in positive control and 40 % mortality in negative control. Larvae put in contact with ultrafiltered solution showed a 55 %. In the case of oyster spat, no mortality was observed in oyster permeate baths: a protection of larvae is obtained with ultrafiltration process.
To conclude, the study demonstrated the efficiency of ultrafiltration to treat OsHV-1 for hatcheries/nurseries. Indeed, the retention is not complete but allows the protection of oyster spat and larvae. Whatever the feed concentration (~105 UFC.mL-1), (i ) the virus concentration in the permeate was below quantification limit, (ii) no mortality was observed in spat in contact with permeate and (iii) mortality rates of larvae were closed to the one obtained with negative control. Ultrafiltration could be use with high efficiency to treat inlet water for shellfish production.
