DAO 141:149-155 (2020)  -  DOI: https://doi.org/10.3354/dao03519

ABSTRACT: White spot syndrome virus (WWSV) has become one of the most widespread causes of mortality in commercial shrimp farming. In the present study, we used PCR to determine the shrimp infectious dose 50% endpoint (SID₅₀ ml^-1) of a Chinese isolate of WSSV in 5 different sizes of pathogen-free Litopenaeus vannamei inoculated intramuscularly. The lethal dose 50% endpoint (LD₅₀ ml^-1) was also determined from the percentage of dead shrimp. The LD₅₀ ml^-1 for 2, 4, 6, 8, and 10 cm shrimp were 10^4.68, 10^5.7, 10^6.70, 10^7.75, and 10^8.81, respectively, and the SID₅₀ ml^-1 were 10^4.68, 10^5.70, 10^6.90, 10^7.75, and 10^8.94, respectively. There was no significant difference between the LD₅₀ ml^-1 and SID₅₀ ml^-1 for each shrimp size, which indicated that all infected shrimp died. The lethal and infectious titer decreased about 1 log₁₀ as shrimp size decreased 1 grade. These data clearly indicate that adult shrimp were more susceptible to WSSV than juvenile shrimp. The horizontal comparison showed that the amount of virus in the shrimp organs increased over the experimental period. The vertical comparison showed that virus quantity was lowest in the organs of 10 cm shrimp and highest in 2 cm shrimp, which indicates that the smaller shrimp had higher levels of viral replication. Hence, the optimal size for WSSV challenge in shrimp inoculated intramuscularly was 2 cm. The determination of virus titers in different sizes of shrimp represents a step towards creating strategies to reduce the negative impacts of WSSV in the aquaculture industry.

KEY WORDS: WSSV · LD₅₀ ml^-1 · SID₅₀ ml^-1 · Litopenaeus vannamei