The molluscan fisheries and aquaculture industries in Australia are threatened by herpesviruses. AbHV caused mass mortalities on Victorian farms from 2005-07 and is endemic off Victorian and possibly Tasmanian coasts. Herpesviruses are known to reactivate under stress conditions, threatening future productivity in the abalone industry and limiting movement of broodstock. Recently, OsHV-1 has been detected in Pacific Oysters in NSW, where it caused mass mortality and threatens the entire Australian oyster industry.
Research in France, where OsHV-1 is endemic, indicates that it is possible to select for higher resistance to this virus in oysters (ie. there is a strong genetic effect on resistance). Work by CSIRO and NSWI&I confirms that resistance to OsHV-1 is under strong genetic control. Screening of resistance level in the context of survivors within selected families is now being incorporated as a component of CRC project 2009/743.
Because molluscs lack acquired immunity, they cannot be vaccinated. The only feasible way to counter the threat of these viruses is to identify and develop resistant populations. As part of our current CRC PhD project (2008/739), we have developed an assay for screening antiviral activity in abalone haemolymph. The next step is to identify antiviral agents in abalone and oysters so they can be used as efficient diagnostic tools for identifying virus-resistant stocks. Biological and chemical screening assays, using antiviral activity and antiviral agent respectively, will be applied to different genetic breeding lines of abalone and oysters. We need to know if these assays could be used to improve resistance and whether genetic improvement of other traits such as growth rate might be compromised. Genetic analysis will determine whether haemolymph antiviral activity is under genetic control, is positively correlated with survival after challenge, and whether there are any undesirable associated effects.
Final report
The project examined the genetic basis of antiviral resistance in oysters and abalone in response to the significant disease threats posed by oyster and abalone herpesviruses. Laboratory-based systems for the growth and assay of such viruses are problematic. The project undertook to measure the antiviral activity of different breeding lines of oysters and abalone using as a proxy measure the antiviral activity against the human herpesvirus HSV-1. We demonstrated that oysters and abalone have antiviral activity against HSV-1, and that this trait is heritable. We identified a hemolymph compound providing antiviral activity. Our analysis of the oyster genome identified what is likely to be a key role for the protein viperin in resistance to viral infection. The project has provided outstanding value in three important areas. First, in adding to the knowledge base directing mollusc breeding programs. Second, in enhancing knowledge of molluscan immunity to viral infections. Third, in building research and development capacity in the Australian seafood industry.
