ABSTRACT

Aquatic food products are the fastest growing of the food-producing sectors, and an important food source for human consumption. The research described in this dissertation demonstrates the interactions of the Pacific white shrimp, Litopenaeus vannamei (L. vannamei) with two devastating viruses, Infectious myonecrosis virus (IMNV) and White spot syndrome virus (WSSV). Viral diseases cause tremendous negative impacts on the shrimp farming industry and these two virus have caused more that $16 billion in losses. Thus, development of strategies to prevent and control viral diseases is of tremendous interest and importance for the sustainability of this industry by utilizing RNA interference as a tool. To understand the underlying mechanisms of host-virus interactions, the transcriptome of lymphoid organ from shrimp infected with IMNV have been analyzed as described in the first manuscript that characterizes newly revealed sequences in the IMNV genome. This paper provides evidence that additional sequences exist in the IMNV genome resulting in an overall genome length that is 8226 base pair (bp) as compared to the original description of 7561 bp. The second manuscript describes variation in virulence among geographically distinct isolates of IMNV from Brazil and Indonesia and the results show that there is a higher virulence in IMNV (Indonesia). The complete genome sequences of both IMNV isolates were compared and shown to differ in 67 bp and 30 amino acid positions. The third manuscript describes the utilization of RNAi to silence WSSV by targeting early gene (wssv477) expression and that is more effective at suppressing virus replication than suppressing late genes (VP15). This result provides a new target antiviral for WSSV. The fourth manuscript presents the development of a direct delivery methodology for double-stranded RNA (dsRNA) into the foregut lumen of L. vannamei. This manuscript indicates that delivery of dsRNA by reverse gavage elicits protection that is comparable to intramuscular injection methods. This method can be used as a proxy for possible per os vaccination trials. The research presented in this dissertation significantly advances the knowledge in host-virus interactions in the Pacific white shrimp and provides promising results toward shrimp disease control strategies.