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April 17, 2013



Viability of Whitespot in Pond Water, Sun-Dried Sediment and Wet Sediment


From Abstract: The viability and infectivity of whitespot syndrome virus (WSSV) in aquaculture environment is not known.  WSSV) is a highly virulent rapidly replicating large, enveloped, double-stranded DNA (dsDNA) virus, causing estimated losses over $6 billion since its emergence in 1992.  Ploughing, tilling and sun-drying of shrimp culture ponds are advocated for prevention and control of whitespot.  Despite this, outbreaks still occur.  Some studies have indicated that WSSV DNA is reported to persist over 20 months in sediments as detected by PCR.  Detection of virus using PCR methods does not indicate its viable nature and ability to infect.


In this study, the viability of WSSV in seawater and shrimp pond sediments under experimentally simulated drainable and non-drainable pond conditions was examined by shrimp infectivity experiments.  WSSV was viable and infective to shrimp in aquaculture pond water for 12 days in seawater of 27 ppt salinity, pH of 7.5 at 29-33°C as revealed by its ability to infect juvenile shrimp; whereas, in shrimp pond sediment, the virus was viable and infective up to 19 days despite sun-drying.  In the case of non-drainable conditions, WSSV remained infective for a period of 35 days.  Although the sediment samples tested nested-PCR positive after 19 days of sun-drying and 40 days under water-logged conditions, shrimp did not show signs of the disease, suggesting that WSSV was not viable.  After 21 days under sun-drying and 40 days under non-drainable experimental conditions, due to reduction in viral load, sediments were positive only by nested PCR, and by this time, viability of WSSV was almost lost as revealed by shrimp infectivity.  Hence, PCR testing of shrimp farm sediment before starting culture may help in ensuring biosecurity from WSSV.


Source: Aquaculture.  Viability of White Spot Syndrome Virus (WSSV) in Sediment During Sun-Drying (Drainable Pond) and Under Non-Drainable Pond Conditions Indicated by Infectivity to Shrimp. S. Satheesh Kumar, R. Ananda Bharati, J.J.S. Rajan, S.V. Alavandi (email, Central Institute of Brackishwater Aquaculture, Indian Council of Agricultural Research, 75, Santhome High Road, Raja Annamalai Puram, Chennai – 600 028, India), M. Poornima, C.P. Balasubramanian and A.G. Ponniah.  In Press, Accepted Manuscript.  Available Online, April 11, 2013.


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