Detection and quantification of shrimp hemocyte iridescent virus by TaqMan probe based real-time PCR

Shrimp hemocyte iridescent virus (SHIV) is a recently reported shrimp virus, which threats the cultured white-leg shrimp Litopenaeus vannamei and can cause huge economic loss in shrimp farming industry in China. A quantitative real time polymerase chain reactio (qPCR) assay was developed using a TaqMan probe to detect and quantify SHIV. A pair of qPCR primers, which amplify a 188 bp DNA fragment, and a TaqMan probe were selected from ATPase gene (ORF114R) of the SHIV genome. The primers and TaqMan probe used in this assay were shown to be specific for SHIV and did not react with White spot syndrome virus (WSSV), Infectious hypodermal and hematopoietic necrosis virus (IHHNV), Hepatopancreatic parvovirus (HPV), Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (VP_AHPND), and Enterocytozoon hepatopenaei (EHP), or healthy shrimp DNA. The detection limit of the qPCR method was as low as 4 copies per reaction. The diagnostic sensitivity and the diagnostic specificity of the qPCR compared with nested PCR were 95.3% and 99.2%, respectively. The resulting standard curves showed high correlation coefficient values (R² = 0.998) in the range of 4 × 10⁹ to 4 × 10⁰ DNA copies/reaction. Test of farm samples showed that SHIV was detected in L. vannamei, Fenneropenaeus chinensis and Macrobrachium rosenbergii contained SHIV ranged from 1.21E+02 to 7.95E+07 copies (μg DNA)^-1. Quantitative detection of different tissues in artificial infected shrimp showed that haemolymph contained the highest SHIV load and muscle contained lowest SHIV load.