Stability of Ostreid herpesvirus-1 (OsHV-1) and assessment of disinfection of seawater and oyster tissues using a bioassay

Microvariant genotypes of Ostried herpesvirus-1 (OsHV-1 μVar) have recently emerged as a cause of epizootic mortality in Pacific oysters (Crassostrea gigas) in many countries. Measures that can reduce the spread of the virus are required to decrease the incidence and distribution of the disease at the local and global scales. Disease management strategies and biosecurity plans require data describing the stability of OsHV-1 in the environment and the methods required for effective disinfection of the virus. A bioassay using intramuscular injection of 10 month old oyster spat had a limit of detection of 3.6 × 103 copies of OsHV-1 genome per oyster. This was 10-fold more sensitive compared to immersion challenge of 5 month old spat, even though the oysters were exposed to a greater volume of inoculum over a period of 2 h. OsHV-1 remained infectious in seawater for 2 days at 20 °C and in wet or dry, non-living oyster tissues for at least 7 days at 20 °C. OsHV-1 was inactivated by: commercial multipurpose disinfectants used according to label directions (Virkon-S, Dupont; quaternary ammonium preparation, Livingston); sodium hydroxide (20 g/L 10 min), iodine (0.1% 5 min) and formalin (10% v/v 30 min); and physical measures including heating to 50 °C for 5 min and exposure to a high dose of ultraviolet light. Ineffective disinfectant treatments were: heating to 42 °C for 5 min, and alkaline detergent (2000 ppm, 10 min) (Pyroneg, Johnson Diversey). Sodium hypochlorite (50 ppm available chlorine, 15 min) inactivated OsHV-1 in relatively clean seawater, but this treatment was not effective after addition of protein, 10% v/v foetal bovine serum. A concentration of 200 ppm available chlorine for 15 min did not inactivate OsHV-1 in oyster tissue. This study provides information that will assist in modelling the disease risk posed by OsHV-1 and data that are necessary to devise effective biosecurity strategies to control the spread of OsHV-1 in a variety of situations. The potential role of fomites in the spread of the virus, and recurrence of disease in endemically infected areas were highlighted by the persistence of infectivity in non-living oyster tissues