Rapid and sensitive detection of Taura syndrome virus using nucleic acid-based amplification

Enzyme-Assisted Nucleic Acid Amplification in Molecular Diagnosis: A Review

Infectious diseases and tumors have become the biggest medical challenges in the 21st century. They are driven by multiple factors such as population growth, aging, climate change, genetic predispositions and more. Nucleic acid amplification technologies (NAATs) are used for rapid and accurate diagnostic testing, providing critical information in order to facilitate better follow-up treatment and prognosis. NAATs are widely used due their high sensitivity, specificity, rapid amplification and detection. It should be noted that different NAATs can be selected according to different environments and research fields; for example, isothermal amplification with a simple operation can be preferred in developing countries or resource-poor areas. In the field of translational medicine, CRISPR has shown great prospects. The core component of NAAT lies in the activity of different enzymes. As the most critical material of nucleic acid amplification, the key role of the enzyme is self-evident, playing the upmost important role in molecular diagnosis. In this review, several common enzymes used in NAATs are compared and described in detail. Furthermore, we summarize both the advances and common issues of NAATs in clinical application.

Improved immunodetection of Taura syndrome virus using a monoclonal antibody specific for heterologously expressed VP1 capsid protein

vp1, a gene encoding one of the capsid proteins of Taura syndrome virus, was cloned into the pGEX-6P-1 expression vector, and the resulting construct was then used to transform E. coli strain BL21. After induction, an N-terminally glutathione-S-transferase-tagged VP1 (GST-VP1) protein with a molecular mass of 80 kDa was obtained. This protein was purified by SDS-PAGE and used for immunization of Swiss mice for monoclonal antibody (MAb) production. Three MAbs specific for the VP1 protein were selected that were suitable for detecting natural TSV infection in Penaeus vannamei by dot blotting, western blotting and immunohistochemistry. This detection occurs without cross-reaction to other shrimp tissues or other common shrimp viruses. As determined by dot blotting, the detection sensitivity of the MAbs was approximately 2 fmole/spot of the GST-VP1. These MAbs showed detection sensitivity comparable to that of MAbs specific for VP2, but they exhibited stronger immunoreactivity than previously studied MAbs specific for VP3. Although the sensitivity of the MAbs to VP1 was 1,000 times lower than one-step RT-PCR, they could be used in various types of antibody-based assays to confirm and enhance the detection sensitivity of TSV infection in shrimp.

Improved sensitivity of Taura syndrome virus immunodetection with a monoclonal antibody against the recombinant VP2 capsid protein

Taura syndrome virus (TSV) is one of the major pathogens causing mortality in the whiteleg shrimp, Litopenaeus vannamei. In this study, the gene sequence encoding the VP2 capsid protein (40 kDa) of TSV was cloned into pMAL-C2 expression vector. Five monoclonal antibodies (MAbs) were produced against the VP2 capsid protein, which was expressed heterologously in the form of a fusion protein with maltose binding protein and called MBP-VP2. All MAbs belonged to the IgG1 subclass and could bind MBP-VP2 at 400-800 pg/spot in immuno-dot blot assays. The MAbs could detect VP2 both in extracts from shrimp infected naturally in western blotting and dot blotting and in shrimp tissues in immunohistochemistry. Additionally, these MAbs did not exhibit cross-reactivity to extracts from uninfected shrimp or shrimp infected with several other common viruses. However, the dot blot assay sensitivity for TSV was approximately 10,000 times lower than that of one step RT-PCR. The MAb TSV2-88 specific to VP2 obtained in this study demonstrated an approximately twofold higher sensitivity than that of the MAb specific to VP3 from a previous study. In immunohistochemistry, the MAb TSV2-88 specific to VP2 demonstrated stronger immunoreactivity than the MAb TSV3-601 specific to VP3. A combination of the VP2 and VP3 MAbs could be used to more easily detect TSV infections in field samples of L. vannamei with better sensitivity and fidelity than using a single MAb.

Immune response of white shrimp, Litopenaeus vannamei, after a concurrent infection with white spot syndrome virus and infectious hypodermal and hematopoietic necrosis virus

In the present study, we investigated immunological changes in viral-infected white shrimp, Litopenaeus vannamei. White shrimp were infected with white spot syndrome virus (WSSV) or co-infected with WSSV and infectious hypodermal and hematopoietic necrosis virus (IHHNV) as detected by polymerase chain reaction (PCR). The complete (100%) mortality rate of shrimp was caused by viral infection due to immune parameters being suppressed including decreases in phenoloxidase activity, total hemocyte counts, differential hemocyte counts, and the gene expressions of prophenoloxidase and peroxinectin. In addition, increases in lipopolysaccharide and beta-1,3-glucan-binding protein of hemocytes and the hepatopancreas, and respiratory bursts per cell, and a decrease in superoxide dismutase were found in viral-infected shrimp, which may have been related to the defense against viral infection.

Specific detection of reverse transcription-loop-mediated isothermal amplification amplicons for Taura syndrome virus by colorimetric dot–blot hybridization

The goal of this study was to develop a field diagnosis system based on isothermal reverse transcription-loop-mediated amplification (RT-LAMP) for shrimp Taura syndrome virus (TSV), placing emphasis on specific and simple detection of the LAMP amplicons. After a single-tube RT-LAMP reaction for TSV was established, colorimetric dot-blot hybridization (DBH) was adopted to detect signals only from the target-derived amplicons. The results showed that the modified DBH offered unambiguous and sensitive detection of the TSV RT-LAMP amplicons without the UV cross-linking and denaturation steps. Together, TSV RT-LAMP-DBH assay reached the same dilution point as reverse transcription-nested polymerase chain reaction-agarose gel electrophoresis (RT-nPCR-AGE) for TSV detection. Specificity of the assay was demonstrated by the absence of DBH signal from yeast tRNA and various shrimp viruses. TSV RT-LAMP-DBH was applied to 125 Penaeus vannamei and demonstrated a very good concordance (kappa value, 0.823) with RT-nPCR-AGE assay in detection efficiency. Furthermore, a one-step guanidinium thiocyanate (GuSCN) homogenization method was established to provide RNA extraction efficiency comparable to that of the TRIzol Reagent for RT-LAMP. Requiring simply a heating apparatus, the GuSCN RNA extraction-isothermal RT-LAMP-DBH protocol has the potential for further development for diagnosis of diseases in the field.