Norovirus (NoV) and pathogenic enteroviruses are the major causes of gastroenteritis in humans worldwide, and are usually transmitted through direct or indirect exposure to raw or partially treated sewage. Filter-feeding shellfish concentrate virus particles from the water and transmit them to humans. The occurrence of norovirus GI and GII and fecal indicators in Louisiana eastern oysters (Crassostrea virginica) and harvest water were investigated on a biweekly basis for almost one year. Only one oyster sample was positive for NoV GII at 3.5 log10genomic copies/g digestive tissues. A stool specimen obtained from an infected individual associated with a norovirus outbreak and the suspected oysters were also analyzed. The norovirus in the stool belonged to GII.4 Sydney; however, the oyster and water were negative and could not be linked. Densities of microbial indicators (fecal coliforms, Escherichia coli, and coliphages) were low, and weakly correlated. A municipal secondary wastewater treatment plant (New Orleans, Louisiana), as a potential source of environmental contamination, was further investigated on a monthly basis for one year. Enteric viruses were detected in the influent and effluent wasters year-round. NoV GII was more abundant than NoV GI, and along with EV increased in influent during fall and spring. NoV GI concentration was higher in influent in fall. Densities of indicator bacteria (enterococci, fecal coliforms and E. coli) did not show strong monthly or seasonal patterns. Averaged monthly removal for enteric viruses and male-specific coliphage ranged between 0.95 and 1.63 log10, and were lower than the indicator bacteria (4.36 log10), indicating higher resistance of viruses to the treatment. Male-specific coliphage was the only indicator that correlated with NoV GII densities in both influent and effluent (r= 0.48 and 0.76, respectively) and monthly removal (r=0.72), indicating that it can be more reliable than indicator bacteria to monitor NoV GII load and microbial removal. Various norovirus genotypes were identified (GI/1, 3 and 4; GII/3, 4, 13 and 21), dominated by GI.1 and GII.4 strains. These observations emphasize the need for direct monitoring of pathogenic enteric viruses in oysters and waters to reduce the risks of viral gastroenteritis incidence.
Naim Montazeri Djouybari, M.Sc.,University of Alaska Fairbanks, 2011, May 2015, submitted to the Graduate Faculty of the Louisiana State University, 117 pages