Evaluation of potential indicators of viral contamination in shellfish and their applicability to diverse geographical areas.

The distribution of the concentration of potential indicators of fecal viral pollution in shellfish was analyzed under diverse conditions over 18 months in diverse geographical areas. These microorganisms have been evaluated in relation to contamination by human viral pathogens detected in parallel in the analyzed shellfish samples. Thus, significant shellfish-growing areas from diverse countries in the north and south of Europe (Greece, Spain, Sweden, and the United Kingdom) were defined and studied by analyzing different physicochemical parameters in the water and the levels of Escherichia coli, F-specific RNA bacteriophages, and phages infecting Bacteroides fragilis strain RYC2056 in the shellfish produced, before and after depuration treatments. A total of 475 shellfish samples were studied, and the results were statistically analyzed. According to statistical analysis, the presence of human viruses seems to be related to the presence of all potential indicators in the heavily contaminated areas, where E. coli would probably be suitable as a fecal indicator. The F-RNA phages, which are present in higher numbers in Northern Europe, seem to be significantly related to the presence of viral contamination in shellfish, with a very weak predictive value for hepatitis A virus, human adenovirus, and enterovirus and a stronger one for Norwalk-like virus. However, it is important to note that shellfish produced in A or clean B areas can sporadically contain human viruses even in the absence of E. coli or F-RNA phages. The data presented here will be useful in defining microbiological parameters for improving the sanitary control of shellfish consumed raw or barely cooked.

Distribution of human virus contamination in shellfish from different growing areas in Greece, Spain, Sweden, and the United Kingdom.

Viral pollution in shellfish has been analyzed simultaneously across a wide range of geographical regions, with emphasis on the concomitant variations in physicochemical characteristics and social features. The methods for sample treatment and for the detection of human enteric viruses were optimized by the participating laboratories. The second part of this study involves the selection of a protocol for virus detection, which was validated by analyzing the distribution and concentration of human viral pathogens under diverse conditions during an 18-month period in four European countries. Shellfish-growing areas from diverse countries in the north and south of Europe were defined and studied, and the microbiological quality of the shellfish was analyzed. Human adenovirus, Norwalk-like virus, and enterovirus were identified as contaminants of shellfish in all the participating countries. Hepatitis A virus was also isolated in all areas except Sweden. The seasonal distribution of viral contamination was also described. Norwalk-like virus appeared to be the only group of viruses that demonstrated seasonal variation, with lower concentrations occurring during warm months. The depuration treatments currently applied were shown to be adequate for reducing Escherichia coli levels but ineffective for the elimination of viral particles. The human adenoviruses detected by PCR correlate with the presence of other human viruses and could be useful as a molecular index of viral contamination in shellfish.

Specific properties of two enteric adenovirus 41 clones mapped within early region 1A.

Enteric adenovirus type 40 (Ad40) and Ad41 form the sixth subgenus of human adenoviruses. They are associated with infantile diarrhea but cannot be isolated in conventional cell cultures. The genome of the fastidious enteric Ad41 has been cloned, and the cleavage sites of the genome produced by restriction endonucleases BamHI, EcoRI, HpaI, NruI, PvuI, and SalI have been mapped. To develop useful hybridization methods for direct detection of adenoviruses, a restriction fragment library containing Ad41 DNA, with plasmid pBR322 as vector, has been constructed. Clones have been isolated which contain 8 of 10 possible BamHI fragments of Ad41, inserted into the BamHI cleavage site of the vector. Two of these clones are particularly useful for the detection of adenoviruses. One clone detects members of all human adenovirus subgenera, and the second clone is specific for enteric adenoviruses, in particular Ad41. A conspicuous absence of detectable homology was noted at 1.5 to 3.3 map units of the Ad41 genome in hybridizations against other serotypes of adenoviruses, including the closely related enteric Ad40. This sequence corresponds to the 5' portion of early region Ia.