Detection of white spot disease virus (WSDV) infection in shrimp using in situ hybridization

The establishment and application of isothermal cross-priming amplification techniques in detecting penaeid shrimp white spot syndrome virus

White spot syndrome virus (WSSV) is one of the main pathogens seriously threatening penaeid shrimp farming in the world. This study designed and synthesized five specific primers based on the conserved sequences of WSSV genome, optimized the reaction system and conditions, and finally established a cross-priming amplification (CPA)-based detection method for WSSV (WSSV-CPA). The results indicated that the optimized reaction temperature and time of WSSV-CPA were 63°C and 60 min, respectively. The detection limit of the WSSV-CPA assay was as low as 10 copies μl(-1) and shared same sensitivity with the WSSV-qPCR assay. Due to dispensing with expensive thermal cycler, time- and cost-saving, and ease of use in field, it is anticipated that the WSSV-CPA method developed in this study will be instrumental for the diagnosis and surveillance of WSSV.

SIGNIFICANCE AND IMPACT OF THE STUDY

White spot syndrome, caused by white spot syndrome virus (WSSV), is the major disease threatening the shrimp aquaculture industry and leads to tens of billion dollars of economic losses in the world each year. This study established a CPA-based method for detecting WSSV, which is rapid, sensitive and specific. It is anticipated that this novel assay will be instrumental for diagnosis and surveillance of WSSV.

Real-time quantitative loop-mediated isothermal amplification as a simple method for detecting white spot syndrome virus

AIMS

White spot syndrome virus (WSSV) continues to be the most pathogenic virus among the crustacean aquaculture causing mass mortality. In the present study, we established a one-step, single tube, real-time accelerated loop-mediated isothermal amplification (real-time LAMP) for quantitative detection of WSSV.

MATERIALS AND METHODS

A set of six specially designed primers that recognize eight distinct sequences of the target. The whole process can be completed in 1 h under isothermal conditions at 63 degrees C. Detection and quantification can be achieved by real-time monitoring in an inexpensive turbidimeter based on threshold time required for turbidity in the LAMP reaction. A standard curve was constructed by plotting viral titre against the threshold time (T(t)) using plasmid standards with high correlation coefficient (R(2) = 0.988).

CONCLUSIONS

Sensitivity analysis using 10-fold dilutions (equivalent to 35 ng microl(-1) to 35 ag microl(-1)) of plasmid standards revealed this method is capable of detecting upto 100 copies of template DNA. Cross-reactivity analysis with DNA/cDNA of IHHNV, TSV, YHV-infected and healthy shrimp showed this method is highly specific for quantitative detection of WSSV.

SIGNIFICANCE AND IMPACT OF THE STUDY

WSSV real-time LAMP assay appears to be precise, accurate and a valuable tool for the detection and quantification of WSSV in large field samples and epidemiological studies.

A review on the morphology, molecular characterization, morphogenesis and pathogenesis of white spot syndrome virus

Since it first appeared in 1992, white spot syndrome virus (WSSV) has become the most threatening infectious agent in shrimp aquaculture. Within a decade, this pathogen has spread to all the main shrimp farming areas and has caused enormous economic losses amounting to more than seven billion US dollars. At present, biosecurity methods used to exclude pathogens in shrimp farms include disinfecting ponds and water, preventing the entrance of animals that may carry infectious agents and stocking ponds with specific pathogen-free post-larvae. The combination of these practices increases biosecurity in shrimp farming facilities and may contribute to reduce the risk of a WSSV outbreak. Although several control methods have shown some efficacy against WSSV under experimental conditions, no therapeutic products or strategies are available to effectively control WSSV in the field. Furthermore, differences in virulence and clinical outcome of WSSV infections have been reported. The sequencing and characterization of different strains of WSSV has begun to determine aspects of its biology, virulence and pathogenesis. Knowledge on these aspects is critical for developing effective control methods. The aim of this review is to present an update of the knowledge generated so far on different aspects of WSSV organization, morphogenesis, pathology and pathogenesis.

A new fluorescent quantitative PCR-based in vitro neutralization assay for white spot syndrome virus

A fluorescent quantitative PCR (FQ-PCR) assay utilizing SYBR green I dye is described for quantitation of white spot syndrome virus (WSSV) particles isolated from infected crayfish, Cambarus clarkii. For this assay, a primer set was designed which amplifies, with high efficiency and specificity, a 129bp target sequence within ORF167 of the WSSV genome. Conveniently, WSSV particles can be added into the FQ-PCR assay with a simple and convenient method to release its DNA. To establish the basis for an in vitro neutralization test, primary cultures of shrimp cells were challenged with WSSV that had been incubated with a polyclonal anti-WSSV serum or with control proteins. The number of WSSV particles released from the cells after these treatments were assayed by FQ-PCR. This test may serve as a method to screen monoclonal antibody pools or recombinant antibody pools for neutralizing activity prior to in vivo animal experiments.

Detection of white spot syndrome virus (WSSV) from hemolymph of Penaeid shrimps Penaeus japonicus by reverse passive latex agglutination assay using high-density latex particles

A simple reverse passive latex agglutination (RPLA) method for detecting white spot syndrome virus (WSSV) in the hemolymph of infected Kuruma shrimp (Penaeus japonicus) was developed. It was confirmed that WSSV could be detected from the shrimp hemolymph when the latex particles blocked with a casein protein were used as detection reagent. It became clear from the result of the infection trial that viruses are detectable by RPLA before the appearance of overt symptoms of this disease. In addition, an amplification product of 982 bp (s) derived from WSSV by PCR was detected in all the samples in which WSSV was detected by RPLA. This newly developed RPLA assay can examine many samples in a simple manner since hemolymph can be extracted more easily than any other organs. This assay can be used conveniently for virus detection in the culture pond of shrimps or in the field.

Sample taking in invertebrate veterinary medicine

Invertebrates are important as pets of the 1990s but more so from economic, pest, and conservation perspectives. Since diagnosis by clinical examination is often taxing in these species, sample taking provides valuable insight into disease processes. Infection and parasitic diseases can be diagnosed by techniques from simple microscopy through to polymerase chain reaction technology. Cytology, hematology, and clinical chemistry, although not widely practiced, can provide critical baseline data in a disease investigation.