CAO, Z; WANG, S.Y.*; MOORE, A.M.; BRELAND, V.; LOTZ, J.: The Effect of Prior Exposure on the Resistance and Viral Titer of Shrimp to Taura Syndrome Virus

Taura Syndrome Virus (TSV) is a ssRNA virus in the family Picornaviridae that infects penaeid shrimp and can cause high mortality rates at aquaculture facilities. We are interested in the mechanism of viral resistance and whether there is a genetic basis for the resistance. To develop a method to quantify viral load in infected shrimp, a quantitative real-time RT-PCR procedure using a molecular beacon was developed. The amplified fragment was isolated initially from the 3′-end of the TSV genome by Differential Display (DD) using RNA from control and TSV-infected Litopenaeus vannamei. Prior exposure had a significant effect on survival as 100% of the shrimp previously exposed to TSV survived a second exposure compared to 62% survival among naive shrimp. Viral titer was dynamic over time with changes as high as 100-fold over a two day period. Among shrimp with low survivorship to TSV infection, viral titer increased slowly in general, reaching 1 x 10⁸ � 5 x 10⁷ copies by day 10. Among shrimp with high survivorship, there was not a consistent trend in the titer of TSV in the hemolymph. Although it is tempting to attribute the higher survival rate to lowered viral titer, the titer was low to non-detectable only for approximately 50% of the shrimp. Decreased rates of viral replication does not appear to be the sole cause of increased survivorship among shrimp previously exposed to TSV.