Range of Factors at Play in Oyster Deaths

8 December 2010

Preliminary test results have identified some of the factors involved in the current increase in deaths of young oysters on upper North Island marine farms, Ministry of Agriculture and Forestry Response Manager Dr Richard Norman says.

The oyster industry has been experiencing significant losses of spat (juvenile oysters) over November and early December and has been working closely with MAF to establish what’s happening.

MAF believes that the mortality is likely to be caused by a range of factors, triggered by unusually warm water temperatures.

Dr Norman says that using molecular tests and DNA sequencing, the MAF laboratory has identified the presence of ostreid herpesvirus-1 (OsHV-1) in oyster samples from affected farming areas.

“OsHV-1 cannot be transmitted to humans. Despite the name, there is no connection between OsHV-1 and herpes viruses in reptiles, birds and mammals (including people).”

The New Zealand Food Safety Authority confirms that there is no food safety or human health risk associated with this oyster virus. The virus is specific to shellfish and is totally unrelated to the herpes viruses that affect humans and other animals.

All of the samples tested by MAF to date have been negative for relevant OIE (World Organisation for Animal Health) listed mollusc diseases. OsHV-1 is not an OIE listed disease, meaning it is not an issue of concern in oyster trade. It has been found in oysters in many countries including within Asia, North America, Europe and Australia where it has been associated with die-offs.

Dr Norman says the virus is thought to have been in New Zealand for some time, with reports of its presence as early as 1992. “At that time, however, the molecular technology required to confidently confirm the virus was not available.”

There has been no detection of any problem with oysters outside of the affected areas, including New Zealand’s Bluff oysters.

“The oyster industry is clearly facing significant production issues with a predicted shortfall for next year of approximately half of next year’s harvest. MAF will continue to work closely with the industry to identify other causes of the event and ways future production can be managed.”

Questions and Answers

What is OsHV-1?

This virus is a naturally occurring organism that normally lies dormant in the marine waters but it can affect young oysters when they are stressed by their environment. For example, warm seawater, high salinities etc.

OsHV-1 is a totally different virus to the herpes viruses which can affect humans or other animals.

OsHV-1 has likely been in New Zealand for some time and it is thought to have been triggered by current environmental conditions.

Are New Zealand oysters safe to eat?

There is no food safety or human health risk associated with this oyster virus. The virus is specific to shellfish and is totally unrelated to the herpes viruses that affect humans and other animals. The New Zealand Food Safety Authority says that there are no food safety concerns associated with eating New Zealand oysters in light of this new information.

What will this find mean for the oyster industry?

The industry will face significantly reduced harvests next year and will need to develop ways to manage production through the current outbreak and in future.

What is the oyster industry worth?

The 2009 returns were approximately $30 million.

Will there be trade implications for exported oysters?

Our trading partners and the OIE have been informed of the test results to date. OsHV-1 is not listed as an OIE disease of concern to trade. It is present in many countries, including some that we export to.