On the epidemiology and evolution of white spot syndrome virus of shrimp

Bui Thi Minh Dieu

Research output: Thesisinternal PhD, WU

Abstract

WSSV causes a devastating disease in shrimp aquaculture that has spread worldwide and probably increased in virulence over time. Understanding WSSV epidemiology and evolution is therefore important for developing novel intervention and management strategies. Both of these goals require finding suitable molecular markers to identify and discriminate WSSV strains, and hereby help infer their origin and track their spread. Five major variable WSSV genomic loci were evaluated as markers for virus identification and virus spread on different spatiotemporal scales. In this thesis the genetic variation between WSSV isolates from the key shrimp production regions in Vietnam was analyzed. A statistically supported model of spread suggests that multiple introductions of WSSV occurred in central Vietnam, and that the virus radiated out over time to the south and the north. Spurious variation was generated during molecular cloning of WSSV VNTR sequences, while no variation occurred in multiple replicates of PCR amplification of VNTRs. Moreover, VNTR sequences were stable over two passages of infection in vivo, indicating that in vivo cloning can be applied to study heterogeneity within WSSV isolates originating from a single shrimp. Genetic deletion of variable region variants appear to be more stable in extensive farms compare to intensive farms over time, indicating that farm practices affect the evolutionary dynamics of WSSV. Genetic variation between Asian WSSV isolates provides support for evolution of genome size according to a geometric model of adaptation, where incrementally smaller genomic deletions are substituted over time. The relationship between the molecular data and the time of first disease occurrence implies that shrimp transportation played an important role in the quick, long range spread of WSSV. Overall, the thesis results show that WSSV variable loci can be effectively employed as molecular markers to study WSSV spread and evolution on different spatiotemporal scales. However, the markers have different properties and the choice of a suitable marker for a pertinent question is critical.


Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Vlak, Just, Promotor
  • Zwart, Mark, Co-promotor
Award date1 Jun 2010
Place of Publication[S.l.
Publisher
Print ISBNs9789085705642
Publication statusPublished - 2010

Keywords

  • shrimps
  • viral diseases
  • molecular epidemiology
  • genetic variation
  • virology
  • epidemiology
  • shrimp culture
  • aquaculture
  • white spot syndrome virus
  • molecular markers

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