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Molecular epidemiology of white spot syndrome virus within Vietnam

Bui Thi Minh Dieu^1,2,

Hendrik Marks^2,

¹ Biotechnological Research and Development Institute, Can Tho University, 3/2 Street Nr 1, 008471 Can Tho City, Vietnam
² Laboratory of Virology, Wageningen University, Binnenhaven 11, 6709 PD Wageningen, The Netherlands

Correspondence
Just M. Vlak
just.vlak{at}wur.nl

White spot syndrome virus (WSSV), the sole member of the virus family Nimaviridae, is a large double-stranded DNA virus that infects shrimp and other crustaceans. By alignment of three completely sequenced isolates originating from Taiwan (WSSV-TW), China (WSSV-CN) and Thailand (WSSV-TH), the variable loci in the genome were mapped. The variation suggests the spread of WSSV from a common ancestor originating from either side of the Taiwan Strait to Thailand, but support for this hypothesis through analysis of geographical intermediates is sought. RFLP analysis of eight Vietnamese WSSV isolates, of which six were collected along the central coast (VN-central) and two along the south coast (VN-south), showed apparent sequence variation in the variable loci identified previously. These loci were characterized in detail by PCR amplification, cloning and sequencing. Relative to WSSV-TW, all VN-central isolates showed a 8·5 kb deletion in the major variable region ORF23/24, whereas the VN-south isolates contain a deletion of 11·5 or 12·2 kb, compared to a 1·2 or 13·2 kb deletion in WSSV-CN and WSSV-TH, respectively. The minor variable region ORF14/15 showed deletions of various sizes compared with WSSV-TH for all eight VN isolates. The data suggest that the VN isolates and WSSV-TH have a common lineage, which branched off from WSSV-TW and WSSV-CN early on, and that WSSV entered Vietnam by multiple introductions. A model is presented for the spread of WSSV from either side of the Taiwan Strait into Vietnam based on the gradually increasing deletions of both ‘variable regions’. The number and order of repeat units within ORF75 and ORF125 appeared to be suitable markers to study regional spread of WSSV.

These authors contributed equally to this work.

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				H. Marks, O. Vorst, A. M. M. L. van Houwelingen, M. C. W. van Hulten, and J. M. Vlak Gene-expression profiling of White spot syndrome virus in vivo J. Gen. Virol., July 1, 2005; 86(7): 2081 - 2100. [Abstract] [Full Text] [PDF]