Herpes, well-known as a sexually transmitted disease, is a global threat to Pacific oysters (Crassostrea gigas). threatening Pacific oysters worldwide. An outbreak of OsHV-1 herpes was noted in France in 2008, where it killed between 80 to 100 percent of affected oyster beds. Since then, it spread to England, where it killed over 8 million oysters in 2010. The disease has since spread to Australia and New Zealand. It has also been found in Tomales Bay, in Marin County in northern California. The inlet is home to the Tomales Bay Oyster Company, the oldest shellfish farm in the US.
Because oysters cannot be vaccinated, disease-resistant oyster lines are being bred in those places where the virus already exists. Researchers are seeking to identify any genes that may allow the oysters to resist contagion.
Oysters are not only considered a delicacy by human gourmands and thus part of a multi-billion-dollar industry, they also filter sea water by filtering tiny plankton from their environment by processing up to 50 gallons per oyster daily. Oysters improve water quality and contribute to the health of the environment. However, in the water in which they grow are can affect both oysters and humans.
Fortunately, the virus has not yet jumped to human beings. But it can be transferred to other bivalve species.
Native to Asia, Pacific oysters are the most popular and valued oyster for aquaculture across the world. Having been first cultivated in their native range, they have seen been taken to other parts of the world where they have become a successful product of aquaculture. Currently, they are the primary species grown on the west coast of US. Along the Atlantic and Gulf coasts, both wild and cultivated Eastern oysters are produced. Those species, however, are relatively resistant to infectious diseases until OsHV-1 emerged in the early 1990s.
Herpes is causing mega-death among Pacific oysters. OsHV-1 microvariants – mutant variants of OsHV-1 -- are more virulent than the original strain. An OsHV-1 microvariant was first detected in France in 2008, while similar variants have caused mass mortalities of oysters in many European countries. A 2010 outbreak in England killed over eight million oysters.
OsHV-1 microvariants also infect Pacific oysters in New Zealand and Australia. Aquaculture in Tasmania has been crippled. In the US, OsHV-1 has been found in Tomales Bay and an adjacent bay in California. To date the virus, the California OsHV-1 causes mortalities of young Pacific oysters, but is thought to be less virulent than OsHV-1 microvariants.
Scientists and oyster farmers fear the spread of OsHV-1 microvariants elsewhere. Researchers have found that once OsHV-1 is established within a bay, mass death typically occur each year during the summer when water temperatures are warm. Analogous to a human infection, the virus is normally latent and does not manifest itself, much as in the case of human cold sores. With stress, however, virus replicates and cold sores emerge. For oysters, warm summer water conditions appear to reactivate the dormant herpes virus.