Virion composition and genomics of white spot syndrome virus of shrimp

Since its first discovery in Taiwan in 1992, White spot syndrome virus (WSSV) has caused major economic damage to shrimp culture. The virus has spread rapidly through Asia and reached the Western Hemisphere in 1995 (Texas), where it continued its devastating effect further into Central- and South-America. In cultured shrimp WSSV infection can reach a cumulative mortality of up to 100% within 3 to 10 days.One of the clinical signs of WSSV is the appearance of white spots in the exoskeleton of infected shrimp, hence its name.WSSV has a remarkably broad host range, it not only infects all known shrimp species, but also many other marine and freshwater crustaceans, including crab and crayfish. Therefore, WSSV can be considered a major threat not only to shrimp, but also to other crustaceans around the world.The WSSV virion is a large enveloped particle of about 275 nm in length and 120 nm in width with an ellipsoid to bacilliform shape and a tail-like extension on one end. The nucleocapsid is rod-shaped with a striated appearance and has a size of about 300 nm x 70 nm. Its virion morphology, nuclear localization and morphogenesis are reminiscent of baculoviruses in insects. Therefore, WSSV was originally thought to be a member of the Baculovirida e.At the onset of the research presented in this thesis, only limited molecular information was available for WSSV, hampering its definitive classification as well as profound studies of the viral infection mechanism. As the first step towards unraveling the molecular biology of WSSV, terminal sequencing was performed on constructed genomic libraries of its genome.This led to the identification of genes for the large (rr 1) and small (rr 2) subunit of ribonucleotide reductase, which were present on a 12.3 kb genomic fragment (Chapter 2). Phylogenetic analyses using the RR1 and RR2 proteins indicated that WSSV belongs to the eukaryotic branch of an unrooted parsimonious tree and further showed that WSSV and baculoviruses do not