DNA constructs expressing long-hairpin RNA (lhRNA) protect Penaeus monodon against White Spot Syndrome Virus

The use of stable and cost-effective DNA vaccines for silencing genes of White Spot Syndrome Virus (WSSV) in Penaeus monodon through RNA interference has been tested. DNA constructs that express long-hairpin RNA (lhRNA) constitutively in vivo against two WSSV envelop genes vp19 and vp28 (pCMV-VP19-LH and pCMV-VP28-LH) were used to confer protection against the pathogen. A construct expressing lhRNA directed against gfp gene (pCMV-GFP-LH) was used to estimate the non-specific protection and to show that on intramuscular administration the plasmid spreads all across the shrimp body and persists for at least 30 days. Shrimp injected with 10 microg lhRNA expressing constructs were challenged with purified WSSV after 24h and pCMV-VP28-LH provided best protection as evidenced by higher survival, lower viral load and silencing of the target viral gene. At an increased dose (35 microg), this construct showed better protection with 75% survival and 81% silencing of the target vp28 mRNA. The construct could actually reduce the viral copy number from the initial 10(3) to 10(5) copies to 10-100 copies. The non-specific pCMV-GFP-LH also showed improved survival and silencing of viral genes, although its effect was less than one third of pCMV-VP28-LH. Silencing constructs can be a good prophylactic approach in commercial shrimp hatcheries to protect high value brooders and to check the vertical transmission of virus, which is a major route of viral entry. Silencing by lhRNA expressed in vivo, confirms the presence of a functional microRNA pathway in shrimp.