Current Status of Viral Diseases in Asian Shrimp Aquaculture

The giant or black tiger shrimp, Penaeus monodon, was formerly the dominant cultured shrimp species in Asia. Since approximately 2002, it has been essentially replaced by the domesticated American whiteleg shrimp P. vannamei. The change in dominant species has affected disease concerns. For both species, white spot syndrome virus (WSSV) and yellow head virus (YHV) are the most lethal. For P. monodon, the next most important diseases are hepatopancreatic parvovirus (HPV) and monodon baculovirus (MBV). For P. vannamei, they are taura syndrome virus (TSV) and infectious hypodermal and hematopoietic necrosis virus (IHHNV). TSV was introduced to Asia in 1998 by careless importation of shrimp stocks for aquaculture but has not been reported to cause problems with local crustacean species. IHHNV, which is endemic in Asia, is harmless to P. monodon but poses a constant threat to IHHNV-free stocks of P. vannamei if they are hatched and reared in Asia under non-biosecure conditions. An emerging disease for P. monodon is monodon slow growth syndrome (MSGS), a component of which seems to be Laem-Singh virus (LSNV). Infectious myonecrosis virus (IMNV) is a P. vannamei disease, first reported from Brazil but now reported in Indonesia where it was probably introduced by careless importation of shrimp aquaculture stocks. So far, IMNV has not been reported in other Asian countries. Penaeus vannamei nodavirus (PvNV) is a new pathogen first reported from Belize in 2004 with gross and histological signs that are indistinguishable from those of IMNV. The disease has not yet affected Asian culture. A more recent disease of P. vannamei in Asia is abdominal segment deformity disease (ASDD), possibly caused by a yet unknown local virus. * E-mail: [email protected] 230 SEAFDEC International Workshop on Emerging Fish Diseases in Asia Introduction This review presents an overview of current viruses in cultivated shrimp in Asia. To understand the situation, it is important to realize that the three largest shrimp producing countries in Asia (China, Thailand, Indonesia) shifted from cultivating the native giant tiger shrimp, Penaeus monodon, to the exotic American whiteleg shrimp, Penaeus (Litopenaeus) vannamei, in approximately 2002 (Wyban, 2007a,b). The shift resulted in dominance of P. vannamei in the global cultivated shrimp market. The main reason for this shift was linked to the supply of shrimp seed (postlarvae) for farms. Traditionally dominant P. monodon farming was based on postlarvae reared from captured broodstock that often appeared normal but were infected with white spot syndrome virus (WSSV). The broodstock transmitted the WSSV (along with other viruses) to their offspring. Thus, postlarvae used to stock cultivation ponds were often the source of continuing WSSV disease (WSD) outbreaks. This problem was solved by using domesticated and genetically improved stocks of P. vannamei that were specific pathogen free (SPF) of major shrimp pathogens including WSSV. These stocks originated at the Oceanic Institute in Hawaii as a result of cooperative efforts in the US Marine Shrimp Research Program (Moss et al., 2005). The exotic shrimp stocks grew well in the intensive culture systems used in Asia and resulted in an increase in world production of cultivated shrimp, previously dominated by P. monodon (Fig. 1). This increase is rapidly bringing total shrimp aquaculture production near that of the shrimp capture fishery. As an example of the general trend in Asia, P. monodon production in Thailand grew explosively from 1987 until the early 1990s when it was hit by yellow head virus (YHV) and, soon World shrimp production