A new method for quantifying white spot syndrome virus: Experimental challenge dose using TaqMan real-time PCR assay

White spot syndrome virus (WSSV) is an important pathogen in shrimp aquaculture. The susceptibility of crayfish (Procambarus clarkii) was assessed by means of serial dilutions of a solution containing WSSV. A TaqMan real-time PCR was used to quantify the WSSV challenge dose in P. clarkii. The results showed that WSSV copies could be detected at concentrations from 1.365×10(4) to 1.129×10(9) copies/μl. The viral infectivity (LD(50)), measured as the mortality of infected crayfish, indicated 60% mortality in the 10(5) dilution group (1.524×10(5) copies/μl). TaqMan real-time PCR represents a novel standard method, based on the by quantitation of WSSV copies, for determining the appropriate concentration of WSSV for use in infection experiments.