Establishment of threshold infection levels of WSSV in different weight ranges of Penaeus vannamei using quantitative PCR (qPCR)

Abstract

Threshold infection level is the pathogen load of the test animals measured before the appearance of clinical signs and mortality. This study aims to establish the threshold infection levels of WSSV in different weight ranges of Penaeus vannamei using qPCR. Artificial infection experiments were conducted using four weight ranges (3–5 g, 7–8 g, 15–18 g, and 22–25 g). The LD₅₀ of the different weight ranges of shrimps were achieved at viral dilution of 10^-6 and 10^-5 after 216–240 hpi, and the viral loads of these inoculums have a range of 10⁵–10⁶ WSSV DNA copies/g. The viral loads of the samples in the timecourse infection experiments when the mortalities started was determined at 10⁹ WSSV DNA copies/g, while for the survivors was at 10⁶ WSSV DNA copies/g. The threshold infection level of WSSV in shrimp was determined at 10⁷ to 10⁸ WSSV DNA copies/g. It was also found out that the threshold infection level was not weight dependent.