Norovirus is the most common foodborne virus. Large outbreaks of norovirus illness associated with shellfish have occurred in Australia. Fourteen outbreaks of gastroenteritis were associated with oyster consumption in Australia between 2001 and 2008, norovirus was confirmed as the causative agent in most of these.
Recent findings demonstrate norovirus binds to receptors on oyster cells, and large variations in amounts of virus taken up by individuals, suggest that oysters may be genetically predisposed to retaining norovirus. There is an opportunity for developing strategies to minimise contamination of oysters with norovirus such as efforts to breed oysters, or pre-treat oysters with virus inhibitors, so they do not bind large quantities of norovirus. These strategies have not been investigated previously and this research will contribute significantly to the current body of knowledge. The success of such approaches could lead to reductions in human illness from consumption of oysters.
Oyster growing areas that have been closed after being implicated in human outbreaks of norovirus gastroenteritis are required to have three consecutive clear rounds of testing prior to being re-opened for commercial harvesting. Some oyster growing areas have large numbers of cattle and pigs residing in the catchment and the following questions have been raised:
(a) Is the oyster norovirus test able to detect bovine and porcine norovirus which may pose no human health issue?
(b) Do Australian cattle and pigs excrete human norovirus strains?
There are many different human norovirus strains which fall into two major genogroups. Current scientific information suggests that the current oyster norovirus test (specific for genogroup I and II) may cross react with some porcine norovirus strains, but the literature is scant with respect to information on the cross reactivity of bovine norovirus strains.