DAO 68:181-188 (2006)  -  doi:10.3354/dao068181

ABSTRACT: In the past, strategies to control white spot syndrome virus (WSSV) were mostly tested by infectivity trials in vivo using immersion or per os inoculation of undefined WSSV infectious doses, which complicated comparisons between experiments. In this study, the reproducibility of 3 defined doses (10, 30 and 90 shrimp infectious doses 50% endpoint [SID₅₀]) of WSSV was determined in 3 experiments using intramuscular (i.m.) or oral inoculation in specific pathogen-free (SPF) Litopenaeus vannamei. Reproducibility was determined by the time of onset of disease, cumulative mortality, and median lethal time (LT₅₀). By i.m. route, the 3 doses induced disease between 24 and 36 h post inoculation (hpi). Cumulative mortality was 100% at 84 hpi with doses of 30 and 90 SID₅₀ and 108 hpi with a dose of 10 SID₅₀. The LT₅₀ of the doses 10, 30 and 90 SID₅₀ were 52, 51 and 49 hpi and were not significantly different (p > 0.05). Shrimp orally inoculated with 10, 30 or 90 SID₅₀ developed disease between 24 and 36 hpi. Cumulative mortality was 100% at 108 hpi with doses of 30 and 90 SID₅₀ and 120 hpi with a dose of 10 SID₅₀. The LT₅₀ of 10, 30 and 90 SID₅₀ were 65, 57 and 50 hpi; these were significantly different from each other (p < 0.05). A dose of 30 SID₅₀ was selected as the standard for further WSSV challenges by i.m. or oral routes. These standardized inoculation procedures may be applied to other crustacea and WSSV strains in order to achieve comparable results among experiments.

KEY WORDS: Litopenaeus vannamei · WSSV · Experimental inoculation · Intramuscular route · Oral route · LT₅₀ · Probit analysis