Diagnostic tests and epidemiological probes for prawn viruses in Thailand and Australia

• Mahidol University, Thailand
• Network of Aquaculture Centres in Asia Pacific, Thailand
• James Cook University, Australia
• Department of Fisheries, Thailand
• Network of Aquaculture Centres in Asia Pacific, Thailand
• James Cook University, Australia
• Mahidol University, Thailand
• Department of Fisheries, Thailand
• CSIRO Animal Health, Australia

The production of cultured prawns is an increasingly important industry worldwide. Thailand is the world's largest producer, with exports worth about $2500 million. In the past decade, however, disease has emerged as the single most important factor threatening the economic sustainability of prawn farming throughout the world. The World Bank estimated that in 1994 disease wiped out 45% of world production - a loss of about $3800 million. The collapse of the wild prawn fishery in the Yellow Sea has also been connected with disease in the prawn farming industry.

In 1996 the World Aquaculture Society called for greater knowledge of the structure, biology and epidemiology of viruses affecting the prawn farming industry in Asia. Such knowledge would also be important in protecting the small Australian industry which, in 1995-6, is estimated to have lost about 15% of potential production (more than $5 million) through disease.

Most deaths in farmed prawns are caused by White Spot Baculovirus (WSBV) and Yellow Head Virus (YHV). Significant research on the two viruses has been conducted in Thailand and elsewhere in the region. However, control of the two diseases is still limited by inadequate knowledge of the biology of the viruses, the characteristics of their spread, and by the lack of sensitive in-field tests for quick and accurate diagnosis of the presence of the virus.

The project will study two viruses that have caused heavy losses to prawn farmers. The team will use advanced molecular analyses to characterise the two viruses, and any related strains, and then develop and evaluate molecular probes for diagnosing and tracking the virus in the field.

The team will purify viruses and extract their nucleic acids. This material will be used to build gene libraries and undertake mapping of the viral genomes. Then, tests for the viruses will be developed, which will be based on probes to recognise viral DNA or RNA fragments within prawn tissue. The scientists will also use purified viruses to create monoclonal antibodies, which can then become a test for virus particles.

Strains of YHV and WSBV will be compared, including viruses isolated in Australia, and researchers will note similarities between isolates which will be useful in tracking infections and understanding the epidemiology of both diseases.