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Walker, P. and Subasinghe, R. (eds.)

DNA-based molecular diagnostic techniques: research needs for standardization and validation of the detection of aquatic animal pathogens and diseases. Report and proceedings of the Joint FAO/NACA/CSIRO/ACIAR/DFID Expert Workshop. Bangkok, Thailand, 7-9 February 1999.

FAO Fisheries Technical Paper. No.395. Rome, FAO. 2000. 93p.

In efforts to limit trans-boundary movement of pathogens and reduce the economic and socioeconomic impact of disease in aquaculture, there is considerable scope for more effective use of DNA-based methods of pathogen detection. These technologies offer rapid results with potentially high sensitivity and specificity, at relatively low cost. Recognition of these advantages has led to rapid adoption of available DNA-based tests, particularly in shrimp culture for which histological procedures lack specificity and culture-based methods have not been possible. However, few if any of the available tests have been assessed appropriately against other diagnostic methods or standardized and validated for specified applications. In fish and shrimp, type or strain specificity of most tests for pathogens in the Asian region is poorly understood and, in molluscs, there is little information on the significant pathogens and few tests of any kind have been developed. Furthermore, tests presently available are frequently conducted by technicians who may not be sufficiently aware of the need for stringent test protocols or the meaning and limitations of the data generated. Implementation of standardized practices that produce reliable, useful and comparable data will require a significant investment in research, training and infrastructure development. Effective implementation will also be assisted by enhanced communication between aquatic animal health practitioners in the region and scientists with expertise in molecular diagnostic technologies.

This review recommends development by FAO/NACA of 2 programs of managed cooperative research to assist more effective use of DNA-based detection tests. Program A should focus on improving the knowledge base by identification of new and emerging pathogens, relating pathogens in the region to those described elsewhere, and defining the extent of genetic variation between related pathogens in the region. Program B should draw on information currently available or obtained from Program A to develop suitably specific DNA-based diagnostic methods and to evaluate and validate the methods for disease diagnosis and pathogen screening programs.

To increase the availability of scientists and technicians with skills in pathology and molecular diagnostic technologies, the review also recommends development of FAO/NACA-sponsored training programs for staff from key laboratories in the region. Training priorities should be in: i) the use of standard histopathological methods for health screening of fish and molluscs; and ii) the use of standard DNA-based methods for pathogen detection including sample collection, application of test protocols and the analysis and interpretation of test results. Because of the urgency of disease problems and the availability of suitable tests, training in DNA-based methods should focus initially on detection of shrimp pathogens.

The review also recommends the development of a laboratory accreditation program in order to achieve standardization of sampling methods and test procedures. The establishment of reference laboratories will assist accreditation for each of the major pathogens. Laboratory accreditation and training programs should complement the activities of OIE in obtaining internationally agreed test standards for molecular diagnostic technologies.

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