Evaluation of spatial and temporal variation of enteric viruses and protozoa contamination in oysters and mussels in shellfish farming area, Normandy, France

Contamination of shellfish growing area with enteric viruses such as norovirus is a well-known threat to the public health. On the other hand, data on shellfish contamination with protozoa are rare and can also be a potential... [ view full abstract ]

Contamination of shellfish growing area with enteric viruses such as norovirus is a well-known threat to the public health. On the other hand, data on shellfish contamination with protozoa are rare and can also be a potential risk for the consumers. The objective of this study was to evaluate the contamination of oysters and mussels with the human (GI, II and IV) and bovine norovirus, rotavirus and protozoa (C. parvum, T. gondii, G. intestinalis). E. coli was used as an indicator of faecal pollution. The shellfish were collected during one-year period in a growing area in Normandy, France, selected for being sensitive to microbial contamination of human and animal origin.

The DNA extraction method was optimised to detect the protozoa. T. gondii was found in one oyster and one mussel sample collected on December.  The Crysptosporidium and Giardia contamination was not demonstrated, which may suggest weak prevalence of protozoa in costal environment or insufficient sensibility of detection method. NoV GII were found in 12 samples (7 oyster and 5 mussel) at low concentrations (<600 RNA copies/g of TD). The viral contamination was demonstrated in November – March period and corresponds to gastroenteritis outbreak season in human population. The bovine norovirus was detected during the same period in 10 samples (5 oyster and 5 mussel), while no rotavirus was found. No correlation between viral, protozoa and E. coli contamination was observed.

This study suggest that it may be valuable to consider shellfish contamination with protozoa in area impacted with animal contamination.