Efficacy of DNA Vaccine Encoding Koi Herpesvirus Glycoprotein on Common Carp Fingerling by Immersion

Abstract

Koi herpesvirus (KHV) is a herpesvirus which especially infects and causes mass mortality to koi and common carp. Therefore the protection of carp from KHV infection is urgently needed. In this study, we developed an application of DNA vaccine containing gene encoding KHV glycoprotein by immersion method to increase survival of common carp against KHV infection. As many as 400 of 30-day-old common carp juveniles were immersed in the water containing 1.3 x 108 CFU/ml of the killed Escherichia coli cells carrying DNA vaccine. Treatments performed were variation of duration and frequency of DNA vaccine immersion; as follows: 1x 30 minutes, 1x 60 minutes, 1x 90 minutes, 2x 90 minutes, and 3x 90 minutes of immersion treatments. Reverse transcription polymerase chain reaction (RT-PCR) analysis showed that DNA vaccine was successfully expressed among the vaccinated fish. Twenty eight days post vaccination, the fish were challenged by injecting 10-4 ml/fish of KHV. The result demonstrated that vaccination by 30 minutes immersion; allowed the 61% of fish survived, this was significantly different (P<0.05) compared to control (without vaccination), but insignificantly different (P>0.05) compared to those of other treatments. The relative percent survival of vaccinated fish were also similar among different treatments (P>0.05). Vaccination by immersion have increased the survival rate about 2 fold compared to unvaccinated fish control (26.67%). Thus, DNA vaccine was effective delivered by immersion for 1x 30 minutes, and this technique can be useful to level up the resistance to KHV infection in common carp juveniles.