An optimized double-antibody sandwich ELISA for quantitative detection of WSSV in artificially infected crayfish

Developing a rapid, accurate and quantitative method for detecting white spot syndrome virus (WSSV) is extremely urgent and critical for reducing the risk of white spot disease outbreaks. In the present work, an optimized double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) was developed for quantitative detection of WSSV. The method employed rabbit polyclonal antibodies against WSSV as the capture antibody and previously produced anti-WSSV monoclonal antibodies as the detector antibody. A standard curve of the log concentration of WSSV versus OD value was established, which was linear in the concentration range of 120-7680 ng/mL, and the linear regression equation was y = 0.166x - 0.151. Viral proteins in different tissues of crayfish (Procambarus clarkia) post artificial infection with WSSV were quantitatively measured using the DAS-ELISA. WSSV proliferated quickly within 60 h post infection and gradually slowed down afterwards. According to the linear regression relationship, the viral proteins in hemolymph, gut and gonad were firstly able to be quantified at 24 h post infection with the concentrations of 186, 158 and 128 ng/mL, respectively. These three tissues also contained higher viral proteins than the gill, heart, hepatopancreas and muscle during the entire infection period. The viral protein concentration in gut reached the highest level of 6220 ng/mL at 72 h post infection. Real time quantitative PCR was also used to detect the dynamic change of viral copies in crayfish hemolymph post WSSV infection, with similar results for both assays. The developed DAS-ELISA could detect WSSV propagation from initial to moribund stage in infected crayfish and demonstrated potential application for diagnosis of WSSV.