STUDIES ON ENVIRONMENTAL TRANSMISSION OF CHITOSAN/PLGA/pDNA VACCINE COMPLEX AGAINST Edwardsiella tarda

Aquaculture is a well-established industry, contributing a significant income to several countries in Asia and South America. Finfish aquaculture in India mainly depends on the culture of Indian major carps (IMC) in which rohu, Labeo rohita is one of the important species. However, the aquaculture industry is consitently facing the problem of bacterial infections. Edwardsiella tarda is one such pathogen which not only affects aquaculture species but also has a zoonotic concern. In our laboratory, a DNA vaccine against E. tarda was developed with 63% efficacy.  Evaluation studies on environmental transmission of recombinant DNA are mandatory before field application as a vaccine.

In this study, the DNA vaccine was conjugated with chitosan-coated PLGA nanoparticles (Chi/PLGA NPs) for enhancing its uptake during immersion treatment. Nanoparticles were prepared with size and zeta potential of 267.4 nm and 27.1 mV, respectively. The experimental tanks (~100L) were prepared by laying a soil bed of ~8 cm along with 60L water. Chi/PLGA NPs conjugated with the plasmid DNA (Chi/PLGA-pGPD+IFN) were administrated to the rohu fingerlings (~5g) @ 10µg/g body weight via immersion route while the control group was treated with PBS. Soil samples were collected from the experimental tanks at different time intervals (3 h, 3, 7, 14, 30 and 60 days post-vaccination) to confirm the transmission of pDNA to the environment. Environmental DNA (eDNA) was extracted from soil samples and the presence of DNA vaccine was tested by the PCR amplification of vaccine specific fragment. Reconfirmation of the obtained results was done by amplifying another fragment of the DNA vaccine. No DNA vaccine could be detected in the eDNA across the time points tested, suggesting that there is no horizontal transfer of DNA vaccine to the environment.