Characterization of white spot syndrome virus of penaeid shrimp: Genomic cloning and sequencing, structural protein analyzing and sequencing, genetic diversity, pathology and virulence

Abstract

The purpose of this dissertation was to characterize virulence, genomic and protein composition of a newly emerged virus of penaeid shrimp: white spot syndrome virus (WSSV). A partial genomic library, covering approximately 30-50% of the genome, of WSSV isolated from crayfish Orconectes punctimanus, was constructed by digesting viral DNA with endonuclease ClaI and cloning into the system pBluescript-JM109. Three viral inserts of approximately 2.2 kb, 2.8 kb and 6.3 kb, named as QW245, CR44, and QW237 respectively, were sequenced and analyzed. Six geographic isolates of WSSV, from China, India, Thailand, South Carolina, Texas, as well as from crayfish obtained from the US National Zoo in Washington D.C. were compared by electron microscopy (TEM) and SDS-PAGE. All viral isolates contained three major polypeptides of 25, 23 and 19 kDa. A fourth major polypeptide at the 14.5 kDa position was observed in four of the viral isolates. The 19 kDa polypeptide of the crayfish WSSV appeared larger in size than that of the other isolates. Amino acid composition of four of the major structural polypeptides of the South Carolina WSSV was analyzed. The NH₂ terminal amino acids of the 25, 23 and 14.5 kDa polypeptides of the SC WSSV were sequenced as MDLSFTLSVVTA, MEFGNLTNLDVA, and VARGGKTKGRRG, respectively. The genomic composition of the six geographic isolates of WSSV were compared by combining the methods of restriction analysis using nine endonucleases AccI, BglII, ClaI, BamHI, EcoRI, HindII, HaeI, SacI, XhoI and Southern blot hybridization applying three digoxigenin-11-dUTP labeled WSSV genomic probes LN4, C42 and A6. No distinctive difference among five WSSV isolated from penaeid shrimp was detected; differences were observed in the crayfish isolate of WSSV. The virulence of the six geographic isolates of WSSV were compared by per os challenge of Litopenaeus vannamei postlarvae and juveniles, and Farfantepenaeus duorarum juveniles. The Texas WSSV caused higher and more rapid mortalities; the crayfish WSSV caused lower and less rapid mortalities. L. vannamei postlarvae and juveniles were very susceptible to WSSV infection, while Fa. duorarum juveniles showed moderate resistance.