Owens, Leigh, Condon, Kelly, Rai, Praveen, and Karunasagar, Indrani (2015) Diet-delivery of therapeutic RNA interference in live Escherichia coli against pre-existing Penaeus merguiensis hepandensovirus in Penaeus merguiensis. Aquaculture, 437. pp. 360-365.

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Abstract

Penaeus merguiensis hepandensovirus (PmeDV) is a strain of the hepatopancreatic parvoviruses that causes overt mortalities and stunting in survivors in many penaeids around the tropical and temperate world. This study was to investigate if RNA interference (RNAi) could be used to ameliorate pre-existing PmeDV infection in a therapeutic manner rather than in a simultaneous exposure when delivered via live bacteria in pelleted food.

One hundred and fifty Australian Penaeus merguiensis testing positive for PmeDV by PCR were divided into 5 treatment groups which were bled weekly for viral copies measured by real time PCR and treated for 5 weeks with the appropriate RNAi. The treatments were no treatment control, carrier fish oil, plasmid delivered nonspecific RNAi, plasmid delivered specific RNAi and plasmid delivered specific RNAi in live Escherichia coli.

Statistically, the specific RNAi microencapsulated in live E. coli was the best overall treatment against pre-existing PmeDV when delivered in the food. Specific RNAi in bacterial cells had the lowest mortality (P < 0.0001), the highest relative percentage survival (68%), most prawns with no detectable viral copies (53%) and it was equal to the nonspecific RNAi with the lowest viral copies when virus was detected (P < 0.0001). The naked plasmid, specific RNAi and the nonspecific RNAi as plasmids were very similar being the next most protective across all measures. The week of the trial was not significant (P > 0.05), but the week by treatment interaction was (P < 0.05) with the number of RNAi-control prawns significantly increasing viral copies at week 2 whilst copies in other treatments fell. Also, fish oil lost its protective effects by 5 weeks as evidenced by statistically increased number of viral copies.

Overall, this study showed that RNAi microencapsulated in live E. coli and fed via pelleted feed could increase survival of P. merguiensis and lower viral copies in pre-existing infections of PmeDV. This methodology herein should be the simplest for farmers to apply and when utilized, these results should allow farmers to increase yields, profitability and therefore, sustainability.

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