Skim Milk Flocculation Concentrates White Spot Syndrome Virus in Seawater for Detection Using A Monoclonal Antibody Based Flow-Through Assay

Since its emergence, white spot syndrome virus has caused huge loss to shrimp aquaculture. However, these viruses are present in very low copy number in water and hence, concentrating them prior to detection is very much essential. In the present study, skim milk (0.01%) was employed for one step concentration of white spot syndrome virus from seawater under acidic (pH 3.5) and neutral (pH 7.4) conditions. The concentrated virus was detected using a monoclonal antibody based flow-through assay, RapiDot and compared its performance with Polymerase Chain Reaction (PCR). In an invitro experiment, the recombinant VP28 protein of white spot syndrome virus was flocculated successfully by skim milk in 50 mL measuring cylinders and detectable in both sub-surface and floc samples by RapiDot. Further, these results were validated by experimental infection studies using virus infected water for skim milk flocculation and detected the virus in floc samples 6 h earlier by RapiDot, compared to 1-step PCR. Overall, a simple method to concentrate white spot syndrome virus in water by skim milk flocculation for detection by RapiDot has been developed and may be adaptable to field conditions. Keywords: Detection; Flocculation; RapiDot; Recombinant VP28 protein; Skim milk; White spot syndrome virus