1. Introduction
White spot syndrome virus (WSSV) infects various hosts and
spread rapidly, which results in serious loss of the shrimp production
in the world [1e4]. The WSSV can be detected in the
apparently healthy shrimp [1,5e7] and the WSSV load in Fenneropenaeus
chinensis without apparent syndrome was found to be
104 copies mg1 tissue on average by qPCR [5,7]. Meng et al. [6]
assayed WSSV infection in Litopenaeus vannamei and found a high
infection rate (98.89%) with load of less than 105 copies mg1 tissue.
WSSV load in surviving L. vannamei can range from 102 to
106 copies ng1 DNA [8]. Jang et al. [1] detected the WSSV load in
the apparently healthy L. vannamei by qPCR and found 80% of
sampling L. vannamei were WSSV-positive with a mean load of
9.48 103 copies mg1 tissue. Durand & Lightner [8] reported that