The importance of Norovirus and Cadmium in Shellfish and implications to human health
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Shellfish are an important food source however they are known to harbour bacteria, viruses and toxic chemicals that can be detrimental to their human consumers. Oysters have been associated with the gastroenteritis virus Norovirus. New Zealand has some of the highest cases of foodborne illness in the western world.
This study investigated a possible link between periods of high rainfall and reported Norovirus outbreaks in four major cities in New Zealand (Auckland, Wellington, Christchurch and Dunedin) as well as national data. Norovirus is a highly infectious foodborne illness. Outbreaks of norovirus have been linked to the consumption of shellfish, and in particular oysters. Norovirus virions can enter the aquatic environment via sewage as a result of human shedding of the virus. This investigation into rainfall and Norovirus outbreaks found no statistically significant relationship, in a monthly or season setting.
In addition the relationship between environmental cadmium levels and exposure levels in New Zealand was investigated through meta-analysis. Cadmium is a heavy metal commonly associated with the mining of copper and zinc ores. It is found naturally in the environment, in air land and oceans Increased exposure to cadmium is known to have a number of serious detrimental health effects, in particular this study investigates cadmiums immunosuppressive properties. Concentrations in New Zealand were compared with Canada, Italy and the UK to determine if New Zealand has a relatively high cadmium intake. Interestingly environmental levels (soil and oceanic) in New Zealand were low. Cadmium levels were higher in oysters than in mussels, with New Zealand oysters containing the highest concentration of cadmium presented. New Zealanders also had the highest cadmium burdens in the kidneys and the highest daily intakes. A No Observable Effect Level (NOEL) was calculated from mice data and compared to the daily intakes of the four countries. Both Canada and New Zealand were above this level.
Shellfish are a common mechanism for exposure to both Norovirus and cadmium. The levels of cadmium present in the diet of New Zealanders may be sufficiently high to suppress the immune system, making it more vulnerable to infections of enteric diseases such as Norovirus.