title: Fitness and virulence of an ancestral White Spot Syndrome Virus isolate from shrimp.
abstract: White Spot Syndrome Virus, the type species of the virus family Nimaviridae, is a large dsDNA virus infecting shrimp and other crustaceans. Genomic analysis of three completely sequenced WSSV isolates identified two major polymorphic loci, "variable region ORF14/15" and "variable region ORF23/24". Here, we characterize a WSSV isolate originating from shrimp collected in Thailand in 1996 (TH-96-II). This isolate contains the largest WSSV genome ( approximately 312 kb) identified so far, mainly because of its sequences in both major polymorphic loci. Analysis of "variable region ORF14/15" suggests that TH-96-II may be ancestral to the WSSV isolates described to date. A comparison for virulence was made between TH-96-II and WSSV-TH, a well characterized isolate containing the smallest genome ( approximately 293 kb) identified at present. After injection of the isolates into Penaeus monodon the mortality rates showed that the median lethal time (LT50) of TH-96-II was approximately 14 days, compared to 3.5 days for WSSV-TH. When both isolates were mixed in equal amounts and serially passaged in shrimp, WSSV-TH outcompeted TH-96-II within four passages. These data suggest a higher virulence of WSSV-TH compared to TH-96-II. The molecular basis for the difference in virulence remains unclear, but a replication advantage of the 19 kb smaller WSSV-TH genome could play a role.
authors.affiliation: Laboratory of Virology, Wageningen University, Binnenhaven 11, 6709 PD Wageningen, The Netherlands.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Marks
authors.forename: Josyanne J A
authors.initials: JJ
authors.lastname: van Duijse
authors.forename: Douwe
authors.initials: D
authors.lastname: Zuidema
authors.forename: Mariëlle C W
authors.initials: MC
authors.lastname: van Hulten
authors.forename: Just M
authors.initials: JM
authors.lastname: Vlak
mesh_terms: D000818:Animals; D004279:DNA, Viral / Q000737:chemistry / Q000235:genetics; D004195:Disease Models, Animal; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D033561:Penaeidae / Q000821:virology*; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D013785:Thailand; D014774:Virulence; D046848:White spot syndrome virus 1 / Q000302:isolation & purification / Q000472:pathogenicity*
chemical_list: D004279:DNA, Viral