Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/17/2011
Publication Date: 12/1/2011
Citation: Provost, K., Ozbay, G., Anderson, R., Richards, G.P., Kingsley, D.H. 2011. Hemocytes are sites of persistence for virus-contaminated oysters. Applied and Environmental Microbiology. 77:8360-8369. Interpretive Summary: Foodborne viruses are efficiently bioconcentrated from contaminated growing waters by shellfish, thus raw shellfish consumption is a significant risk factor for acquisition of norovirus and hepatitis A. Mechanisms by which viruses can persist within shellfish are not well understood. Depuration by transfer to less contaminated water, a widely applied intervention, does not adequately clear enteric viruses, while fecal bacteria levels are substantially reduced. In this paper, we demonstrate that viruses are located within blood cells of oysters and can remain within these cells for several weeks. Comparing several viral species, it is noted that the more acid-resistant the virus, the more persistent it appears to be within oyster tissues. While this research publication is primarily of a basic nature, understanding how and why foodborne viruses can stay sequestered within oysters may potentially lead to alternate intervention strategies for shellfish.
Technical Abstract: Like fecal bacteria, waterborne enteric viruses are readily bioconcentrated by bivalve shellfish. However while many bacteria decline rapidly when bivalves are placed in uncontaminated water, viruses tend to be retained within shellfish. In this study, we offer evidence that phagocytic blood cells (hemocytes) of the Eastern oyster, Crassostrea virginica, play important roles for the retention of virus particles within bivalves and hypothesize that phagocytized viruses are sequestered and persist within the intracellular phagolysosomes. Hepatitis A virus (HAV) was found to be associated with hemocytes harvested and separated from the hemolymph of HAV-exposed oysters. Transfer of hemocytes from HAV-contaminated oysters to naïve virus-free oysters resulted in the meat of the naïve oyster testing HAV-positive for up to three weeks. Evaluation of the temporal persistence of HAV, murine norovirus (MNV) and poliovirus (PV) within hemocytes correlated with the presence of these viruses in oyster meat. Since phagocytosis would likely result in sequestration of virions within the acidic phagolysosome of the hemocyte, acidic pH tolerance of several viruses (HAV, MNV, PV, and feline calicvirus [FCV]) was evaluated to see if acid tolerance correlates with the virus’ ability to persist within oysters. The degree of viral persistence within oysters and their ability to survive low pH were similar: HAV persisted the longest and was most acid resistant, MNV and PV were less tolerant of acidic pH and persisted to a lesser degree than HAV, while FCV did not persist within oysters and was not acid tolerant.