A TaqMan real-time PCR assay for survey of white spot syndrome virus (WSSV) infections in Litopenaeus vannamei postlarvae and shrimp of farms in different grow-out seasons

A TaqMan real-time PCR was conducted to quantify the white spot syndrome virus (WSSV) infections of three Litopenaeus vannamei hatcheries and 30 commercial grow-out ponds from different farms, during summer and autumn in South Korea. A total of 98.89% postlarvae showed WSSV-positive with very low WSSV infection load, 0.0–34.3 (mean of 3.2) copies/ng DNA, while all farm samples were WSSV-positive with a mean load of 9.8 × 106 and 2.1 × 105 copies/ng DNA in summer and autumn, respectively. In summer, nine (52.9%) farms showed WSSV infections with fewer than 103 copies/ng DNA and a mean shrimp production of 1.05 mt/ha; meanwhile, eight (47.1%) farms showed high infections (i.e., >103 copies/ng DNA) with a mean shrimp production of 0.85 mt/ha. In autumn, a total of eight (61.5%) farms showed infections with fewer than 103 copies/ng DNA, with mean shrimp production of 4.53 mt/ha; five (38.5%) farms showed high infection (i.e., >103 copies/ng DNA), with a mean shrimp production of 0.42 mt/ha. The mean production of autumn farms with infection loads of less than 103 copies/ng DNA, versus that of autumn farms with more than 103 copies/ng DNA, was significantly different (P < 0.05).