title: Virulence and genotypes of white spot syndrome virus infecting Pacific white shrimp Litopenaeus vannamei in north-western Mexico.
abstract: White spot syndrome virus (WSSV) has caused substantial global economic impact on aquaculture, and it has been determined that strains can vary in virulence. In this study, the effect of viral load was evaluated by infecting Litopenaeus vannamei with 10-fold serial dilution of tissue infected with strain WSSV Mx-H, and the virulence of four WSSV strains from north-western Mexico was assessed along with their variable number of tandem repeat (VNTR) genotypes in ORF75, ORF94 and ORF125. The LD50of the Mx-H strain was a dilution dose of 10-7.5; the mortality titre was 109.2LD50per gram. In shrimp injected with 102.5to 106.5LD50, no significant virulence differences were evident. Using mortality data, the four WSSV strains grouped into three virulence levels. The Mx-F strain (intermediate virulence) and the Mx-C strain (high virulence) showed more genetic differences than those observed between the Mx-G (low-virulence) and Mx-H (high-virulence) strains, in ORF94 and ORF125. The application of high-viral-load inocula proved useful in determining the different virulence phenotypes of the WSSV strains from the Eastern Pacific.
authors.affiliation: Laboratorio de Análisis de Sanidad Acuícola, Departamento de Ciencias Agronómicas y Veterinarias, Instituto Tecnológico de Sonora, Ciudad Obregón, Sonora, México.
authors.forename: J
authors.initials: J
authors.lastname: Ramos-Paredes
authors.affiliation: Laboratorio de Ecología Molecular, Departamento de Investigaciones Científicas y Tecnológicas, Universidad de Sonora, Hermosillo, Sonora, México.
authors.forename: J M
authors.initials: JM
authors.lastname: Grijalva-Chon
authors.affiliation: Laboratorio de Análisis de Sanidad Acuícola, Departamento de Ciencias Agronómicas y Veterinarias, Instituto Tecnológico de Sonora, Ciudad Obregón, Sonora, México.
authors.forename: J C
authors.initials: JC
authors.lastname: Ibarra-Gámez
mesh_terms: D000818:Animals; D001483:Base Sequence; D005814:Genes, Viral / Q000235:genetics*; D005838:Genotype; D008800:Mexico; D016366:Open Reading Frames; D033561:Penaeidae / Q000821:virology*; D014774:Virulence; D046848:White spot syndrome virus 1 / Q000235:genetics* / Q000472:pathogenicity*
keywords: 
  LD
  50
  ; 
  Litopenaeus vannamei
  ; WSSV genotypes; WSSV strains; viral load; virulence assessment