Immersion immunization of koi (Cyprinus carpio) against cyprinid herpesvirus 3 (CyHV-3) with carbon nanotube-loaded DNA vaccine

Koi as a popular ornamental fish were threatened by the emergence of a deadly disease caused by cyprinid herpesvirus 3 (CyHV-3; initially called koi herpesvirus or KHV), while there is no effective drug or vaccine against this fatal disease at present. Meanwhile, many drugs and vaccines had no effect in many cases account of several impenetrable barriers (cell, skin and gastrointestinal tract). Here we reported an immersion DNA vaccine system encoding a plasmid (pcDNA) coupled with ORF149 gene of KHV based on single-walled carbon nanotubes (SWCNTs). To evaluate its efficacy against KHV, we set 9 different treatment groups contained PBS, pcDNA3.1 vector, inactivated virus, 1, 5, 10 mg/L of pcDNA3.1-ORF149, 1, 5, 10 mg/L of SWCNTs-pcDNA3.1-ORF149. The juvenile koi fish (3.0 ± 1.0 g) was vaccinated via immersion (100 fish per tank with 8 L rearing water). We found a stronger and longer duration immune response (serum antibody production, enzyme activities and immune-related genes expression) can be induced in fish vaccinated with high concentration SWCNTs-p149 in comparison with those vaccinated with p149 alone. The vaccine conferred an 56% protection against intraperitoneal challenge with 50 μL dose live KHV virus (7.3 × 105 TCID50/mL), which is the highest in the experiment. Thereby, this study demonstrates that SWCNTs as a promising carrier for DNA vaccine against KHV might be used to vaccinate large-scale juvenile koi fish by bath administration approach, which will effectively alleviate the pressure of the severe situation of KHV control.