Early diagnosis of white spot viral syndrome using rapid gill staining technique

摘要

White spot viral syndrome caused by the white spot syndrome virus (WSSV) is the major cause of mortality and morbidity in shrimps, resulting in huge losses to shrimp farmers in coastal areas. It has been reported that during 1994-95, this disease struck the booming aquaculture industry and caused a loss of around 20,000 tons of shrimp worth about Rs 25 0-3 50 billion. This is a dreadful disease and is difficult to identify in the early stages. The diagnosis of viral infection is made possible with PCR and monoclonal antibody-based techniques, but these methods are expensive and the facility is not available everywhere. Early diagnosis will provide an opportunity to manage the disease in a comparatively better manner and will also help in preventing the rapid spreading of the disease. In general, the prevalence of WSSV can be observed by visual symptoms like appearance of white spots on the carapace and other external parts of the body. However, diagnosis at this stage of infection is of no use, as the shrimps start dying due to the disease. Thus, diagnosis of WSSV before it shows external symptoms is of practical significance. This will be useful at least to regulate the disease in the preliminary stage. In the present correspondence, a tool for rapid diagnosis of WSSV has been described as a reproducible protocol for the aqua industry. Diagnosis of the disease can be made by adopting wet squash preparation of the tissue and observing it through a microscope after fixing and staining the tissue for observation of hypertrophied nuclei (symptom for WSSV), as the WSSV is known to replicate in the nucleus of the host by forming inclusion bodies. This is a novel method of identification of infection in the asymptomatic phase using a nuclear stain, developed in our laboratory based on the principles of existing stains. For developing the stain, the components were mixed in the proportions shown in Table 1.