Enteric Viruses and Management of Shellfish Production in New Zealand

In New Zealand shellfish are a significant food resource and shellfish are harvested for both recreational and commercial use. Commercially harvested Greenshell mussels (Perna canaliculus) and Pacific oysters (Crassostrea gigas) from aquaculture farms dominate consumption in New Zealand. Other commercial species include cockles (Austrovenus stuchburyii) and surf clam species which are wild harvested. The consumption of shellfish has been associated with gastroenteritis outbreaks caused by noroviruses following faecal contamination of growing waters with human waste. In New Zealand, since 1994 over 50 norovirus outbreaks linked to consumption of either New Zealand commercially grown oysters or imported oysters have been reported. An IEC/ISO 17025 accredited method for detection of noroviruses in bivalve shellfish was established in 2007. This method has been used in outbreak investigations to analyse implicated shellfish, in virus prevalence surveys and monitoring programmes, and commercially for product clearances. Surveys have shown that enteric viruses occur frequently in non-commercial shellfish, especially near sewage outfalls and following sewage discharge events. Viral source tracking methods have assisted in identifying pollution sources. The commercial shellfish industry operates under the Bivalve Molluscan Shellfish Regulated Control Scheme (BMSRCS), administered by the New Zealand Food Safety Authority. Recently regulatory measures were introduced into the BMSRCS to manage viruses. These include the closure of harvest areas for at least 28 days after human sewage contamination events and norovirus outbreaks. These management strategies, coupled with new information on norovirus prevalence in shellfish, have helped to improve the quality and safety of New Zealand shellfish.