Herpes to blame for oyster deaths
Posted on 08. Dec, 2010 by Doctor in Herpes Treatment
An incurable herpes-like virus is behind the widespread deaths of juvenile Pacific oysters — in upper North Island marine farms, scientists say.
The $30 million industry disclosed last week that it has been experiencing big losses of juvenile oysters over November and early December. Half the aquaculture industry’s farmed oysters due for harvest next year have died on marine farms from Parengarenga Harbour in Northland to Ohiwa in the eastern Bay of Plenty.
On some farms, up to 80 percent of juvenile oysters had died, compared with 5 percent to 10 percent in a normal year.
Marine pathologists at the Ministry of Agriculture and Forestry have used molecular tests and DNA sequencing to show the presence of ostreid herpesvirus-1 (OsHV-1) in samples from affected oyster farms, and MAF response manager Richard Norman said it was possible the die-off had been due to a range of factors, triggered by unusually warm water temperatures.
Oyster herpes virus is specific to shellfish and is not unrelated to the herpes viruses that affect humans and other animals.
A strain of the virus killed between 20 to 100 percent of breeding Pacific oysters in some French beds in 2008, 2009, and 2010.
That virus has since has spread into British waters.
Ostreid herpes viruses are known to affect not only oysters but also clams, scallops, and other molluscs, according to French Research Institute for Exploitation of the Sea pathology lab director Tristan Renault, who has suggested in Europe that global warming “could be an explanation of the appearance of this particular type of the virus”.
Animal health experts at the European Food Safety Authority (EFSA) are assessing the extent to which a combination of “infectious agents” such as OsHV-1 and environmental factors are causing the die-off of Pacific oysters there, whether other shellfish species are involved and the risk of infection posed by the transfer of adult Pacific oysters from infected farms.
But MAF said today that OsHV-1 was not listed as a mollusc disease by the World Organisation for Animal Health (OIE), “meaning it is not an issue of concern in oyster trade”.
“The oyster industry is clearly facing significant production issues with a predicted shortfall for next year of approximately half of next year’s harvest,” said Dr Norman. “MAF will continue to work closely with the industry to identify other causes of the event and ways future production can be managed.”
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