The Penaeid Shrimp Viruses TSV, IHHNV, WSSV, and YHV

Abstract

ABSTRACT Viral diseases have emerged during this decade as serious economic impediments to successful shrimp farming. While nearly 20 distinct viruses or groups of viruses are known to infect penaeid shrimp, only four, WSSV, YHV, IHHNV, and TSV, pose a threat to the future of penaeid shrimp culture in the Western Hemisphere. TSV and IHHNV have caused serious disease epizootics throughout the Americas and Hawaii. IHHNV was described nearly 20 years ago when it was found to be responsible for cumulative losses of cultured Penaeus stylirostris that often exceed 90%. The threat of high mortalities posed by IHHNV has historically curtailed interest in the culture of this species in favor of the more IHHNV-resistant P. vannamei. While relatively resistant, IHHNV nonetheless infects P. vannamei and causes runt deformity syndrome (RDS) in which affected shrimp display reduced growth, highly variable sizes, lower production, and sometimes reduced survival. Taura Syndrome in P. vannamei is the virtual “mirror image” of IHHN disease in P. stylirostris. Following its recognition in 1992 as a distinct disease of P. vannamei in Ecuador, Taura Syndrome and its viral agent TSV spread rapidly throughout many of the shrimp farming regions of the Americas. Cumulative mortalities due to TSV in affected juvenile P. vannamei populations have ranged from 40 to 95%. Because P. stylirostris was found to be innately TSV-resistant, genetically selected IHHNV-resistant lines of this species disease are being developed and marketed in the Americas. Some shrimp farmers are using domesticated, selected stocks of P. vannamei that show improved resistance to TSV, while others have continued to use wild stocks that are also showing increased resistance, perhaps through intense natural selection. The viruses of the Yellow Head Disease (YHV) and the White Spot Syndrome (WSSV) were first recognized in 1991-92 in Asia, and by 1996 the two diseases had spread and had caused major pandemics throughout much of the shrimp farming regions of East Asia, Southeast Asia, Indonesia, and India. In late 1995, WSSV was found in North America for the first time in P. setiferus at a shrimp farm in south Texas. WSSV has since been detected in cultured and wild shrimp, crabs, and freshwater crayfish at multiple sites in the eastern and southeastern U.S., as well as being commonly found (along with YHV) in imported frozen commodity shrimp. Because Western Hemisphere penaeids are highly susceptible to WSSV and YHV, the introduction and establishment of either of the viruses poses a significant threat to the shrimp farming industry. The available detection methods for IHHNV, TSV, WSSV, and YHV include traditional methods that employ gross signs, clinical history, histopathology, and bioassay with susceptible shrimp hosts. Molecular and serological methods have also been developed, and specific gene probes, monoclonal antibodies, or PCR methods are readily available for each of the four viruses.