Researchers from the United States Food and Drug Administration have found that oysters undergo physiological changes from November through January that cause them to accumulate greater levels of pathogens than in warmer months. They report the results of their research in the April 2000 issue of the journal Applied and Environmental Microbiology . The researchers tested the ability of eastern oysters from the Gulf of Mexico to accumulate microorganisms that are common indicators of fecal contamination over the course of one year. Fecal contamination is a common cause of gastrointestinal illness. They found that the oysters had a significantly greater ability to accumulate these microorganisms from the period beginning in late November through January.
Oysters are filter-feeding animals that can filter several liters of seawater daily.
These findings suggest that the seasonal occurrence of shellfish-related illnesses by enteric viruses is, in part, the result of seasonal physiological changes undergone by the oysters that affect their ability to accumulate viral particles from estuarine waters. And K.R. Calci. Selective accumulation may account for shellfish-associated viral illness.