A form of herpes has been identified as the likely cause for the deaths of vast numbers of juvenile Pacific oysters around the North Island, Ministry of Agriculture and Forestry (MAF) has confirmed.



In a statement this morning MAF response manager Dr Richard Norman said that Ostreid herpesvirus-1 (OsHV-1) the virus had been detected on a number of oyster farms around the upper North Island using molecular testing and DNA sequencing.



Norman insisted there was no risk to humans.



''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),'' he said.



According to MAF the New Zealand Food Safety Authority had confirmed there was no health risk from eating the shellfish.



MAF would continue to work with the industry to work out how to deal with the situation, Norman said.



Documents on the World Organisation for Animal Health website show that the virus has been identified on 12 oyster farms in Waikato, Northland and Auckland.



On some of the farms where the virus had been identified, the entire population of spat, which were due for harvest in around 12 months, have been killed by the virus. On all of the sites where the virus had been identified the death rate was at least 50 per cent.

In the last month oyster farms from Waikato to the eastern Bay of Plenty have been discovering that high numbers of juvenile oysters have died.



In an interview with Bloomberg, several hours before the MAF announcement, Biosecurity Minister David Carter said the virus may have been present in the country for years.



It was likely to cause ''significant financial impact'' on the industry, which generates around $26 million in revenue a year, more than half from exports, Mr Carter reportedly said.



Last week marine disease experts at MAF confirmed they had taken more than 250 samples and were urgently trying to find out the cause of the deaths.



So far there have been no restrictions placed on harvest.

Oyster Association chairman Callum McCallum said the virus had been present around the world, including in New Zealand in the early 1990s.



It appeared the recent deaths may have been caused by a combination of factors, including last month's drought around the upper North Island, McCallum said.

McCallum has warned that because oysters tend to be farmed in remote areas, the deaths are likely to have a severe impact on communities where there are few employment options.



So far there have been no signs that the Bluff Oysters are affected.