Oyster Herpes Threatens NZ

Of the 12 outbreaks, the virus has mostly affected youngstock, with only a smaller percentage of older oyster being affected.

Mortality rates have caried between 80 to 100 per cent.

The Ministry of Agriculture and Forestry Biosecurity New Zealand (MAFBNZ) is investigating a syndrome of increased mortality in Pacific oysters (Crassostrea gigas) reported to be more severe in younger oysters and, potentially, at elevated water temperatures.

Normal mortality on farms is between five and ten per cent – there is varying die-back, but losses of over 80 per cent of all spat (baby oysters) have been observed.

The die-back has only been observed in farmed oysters and has not been found in wild populations, including the Bluff oyster (Tiostrea chilensis).

The New Zealand Food Safety Authority advises there is no evidence to suggest any food safety concern in New Zealand oysters, whether distributed for local consumption, or exported.

The MAFBNZ and the marine farming industry, through the industry body Aquaculture New Zealand, are working closely to get to the cause of the problem and establish how to manage the situation moving forward.

The Investigation and Diagnostic Centre, Wallaceville, has identified, by polymerase chain reaction (PCR) and DNA sequencing, the presence of ostreid herpesvirus-1 (OsHV-1) in association with affected farming areas. It is intended that this identification is further confirmed by repeat molecular testing at an independent reference laboratory in Australia.

All of the samples tested by the MAFBNZ to date have been negative for relevant OIE-listed mollusc diseases including Marteilia refringens (type O), Bonamia species and Perkinsus species.

Histopathology has not identified the presence of any Haplosporidian species. In addition, the laboratory is using a range of techniques to identify any other pathogens that could be associated with this event.