Abstract:
There have been a number of outbreaks of gastroenteritis related to the consumption of Pacific oysters contaminated with human enteric viruses in New Zealand. These outbreaks can have a serious impact on public health and cause loss of income for the implicated shellfish growing area. There is little known about the relative uptake, inactivation, and elimination of different human enteric viruses by Pacific oysters, and information regarding the distribution and sub-cellular location of these viruses in Pacific oysters is also limited.
A series of bioaccumulation and depuration experiments were undertaken to address these knowledge gaps around the biology of virus uptake in Pacific oysters. In situ experiments showed that norovirus (NV) and poliovirus (PV) were predominantly located within the lumen and cells of the oyster digestive tract tissues, and were also present in cells of several non-digestive tract tissues. Delivery-rate experiments showed that oysters subject to longer bioaccumulation times contained significantly higher levels of virus in the gill, labial palp, and mantle tissues than oysters exposed to the same amount of virus over a shorter time frame. Additional experiments suggested that the majority of the PV present in the oyster gut was non-viable, whereas only a small portion of hepatitis A virus (HAV) detected in the oyster gut was non-viable. The results from depuration experiments showed a large drop in the amount of PV in the gut over a 23 h cleansing period, in marked contrast, oysters contaminated with HAV and NV showed no significant loss of virus.
These experiments suggest that long-term seepage of sewage into oyster growing areas may result in higher levels of virus in oyster tissues than short-term spill events. The different patterns of uptake and elimination of HAV, NV, and PV may result from subtle differences in the interactions of the viruses with oyster cells and this highlights the fallibility in using surrogate pathogens to estimate the risk associated with faecal contamination of shellfish. Given the increasing economic importance of Pacific oysters, and the importance of kaimoana to New Zealanders, this additional knowledge on the biology of oyster-virus interactions in the New Zealand setting provides positive direction for both future research and the refinement of risk management strategies.
