Virus-associated White Spot Syndrome of Shrimp in Taiwan: A Review.

Abstract

White spot syndrome (WSS) is a viral disease which affects most of the commercially cultivated marine shrimp species, not just in Taiwan but globally. The principal clinical sign of WSS is the presence of white spots on the proximal surface of the cuticle of the diseased shrimp. The causative agent is a dsDNA virus which consists of an enveloped, rod-shaped nucleocapsid. White spot syndrome virus (WSSV) infection is character ized by rapid disease onset and high mortality. The mortality typically reaches 90% within 2 to 7 days after the onset of the disease. Recently, WSSV was also found in the form of a latent infection in freshly caught wild shrimp and crabs. Under stressful conditions, WSSV was triggered to replicate rapidly and subsequently caused the death of these animals. Using polymerase chain reaction (PCR), we successfully detected WSSV in cultured and captured shrimp and crabs. Detection of WSSV in non-cultured arthropods collected from WSSV-affected shrimp farms revealed that copepods, the pest crab Helice tridens, small pest palaemonid prawns, and possibly the larvae of an ephydrian insect were reservoir hosts of WSSV. The tissues targeted by WSSV originate from both the ectoderm and the mesoderm. In situ hybridization and transmission electron microscopy (TEM) showed evidence of WSSV in the reproductive organs of black tiger shrimp Penaeus monodon. Since infected oocytes either undergo necrosis or fail to develop to maturity, transovarial transmission is an unlikely pathway. Transovum transmission is a very real possibility, however, and perhaps one of the most effective ways of dealing with this is simply to rinse or disinfect the nauplii.

Development of a Real-time PCR Assay for the Detection and Quantification of Red Seabream Iridovirus (RSIV).

“…In recent years, conventional PCR has been routinely used in screening broodstock to be used in hatcheries (Hsu et al, 1999;Muroga, 2001). This tech nique can have false-negative results (Lo and Kou, 1998), and so there is a need for a more sensitive assay than conventional PCR. The present real-time PCR assay to detect and quantify RSIV should be useful for examining cultured fish for the presence of the virus at the early stages of infection because of its higher sensi tivity and specificity than that achieved with conventional PCR.…”

Relationship between white spot syndrome virus and indicators of quality in Penaeus monodon postlarvae in Karnataka, India

“…As a result, screening of postlarvae (PL) and broodstock for the presence of WSSV has been recommended as part of a strategy to reduce the amount of virus introduced into shrimp farming systems (Limsuwan 1997, Lo & Kou 1998, Withyachumnarnkul 1999. Other proposed methods for reducing the risk of WSD are forma-lin treatment (Limsuwan 1997) and quality assessment tests (Chanratchakool et al 1998).…”

Control of Penaeid Acute Viremia (PAV) in Penaeus japonicus: Selection of Eggs Based on the PCR Detection of the Causative Virus (PRDV) from Receptaculum Seminis of Spawned Broodstock.

“…The increase in detection rate of PRDV in the receptaculum seminis is caused by the multiplication of the virus during the spawning, probably due to stresses from handling and spawning, or by the reduction in the amount of sperm, which will disturb PCR reaction with insufficient DNA extraction. In P. monodon, it was suggested that infected egg cells are killed by WSBV before maturation (Lo et al, 1997), and that rinse or disinfection of the nauplii is one of the most effective way as a preventive measure of the disease in seed production (Lo and Kou, 1998). How ever, in P. japonicus, it was found that disinfection of the nauplii with povidone-iodine gave a serious damage to their survival (data not shown).…”