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The bacterium, Vibrio tapetis, is the aetiological agent of Brown Ring Disease (BRD), which affects the Manila clam, Venerupis (Ruditapes) philippinarum. Two PCR assays for detection of V. tapetis were applied to a sample of 52 Manila clams, and evaluated in comparison with the more traditional V. tapetis detection method of microbiological isolation and characterization, as well as the traditional BRD diagnostic technique of shell valve analysis. The pathogen was detected in 15.4% of the sample using the PCR assay of Rodríguez et al. (2003, 2006) in 50% of the sample using the PCR assay of Paillard et al. (2006) and in 36.5% of the sample by microbiological methods. Whereas shell valve analysis was the least sensitive technique, detecting BRD in 7.7% of the sample, it was an essential diagnostic tool because it was the only technique that identified the disease, rather than the aetiological agent. None of the four techniques was sufficient on its own for effective BRD diagnosis; rather various combinations of two techniques were the minimum required. The combination of shell valve analysis with the assay of Paillard et al. (2006) proved to be the most sensitive and rapid of those tested. Shell valve analysis was the most time-efficient and cost-effective technique, whereas microbiological characterization was the most time-consuming, and PCR detection, using either set of primers, the most expensive. These results may need to be considered in light of diagnosis and management of BRD. [ABSTRACT FROM AUTHOR]