Plant-Produced Vaccines: Future Applications in Aquaculture

Aquaculture has undergone rapid development in the past decades. It provides a large part of high-quality protein food for humans, and thus, a sustainable aquaculture industry is of great importance for the worldwide food supply and economy. Along with the quick expansion of aquaculture, the high fish densities employed in fish farming increase the risks of outbreaks of a variety of aquatic diseases. Such diseases not only cause huge economic losses, but also lead to ecological hazards in terms of pathogen spread to marine ecosystems causing infection of wild fish and polluting the environment. Thus, fish health is essential for the aquaculture industry to be environmentally sustainable and a prerequisite for intensive aquaculture production globally. The wide use of antibiotics and drug residues has caused intensive pollution along with risks for food safety and increasing antimicrobial resistance. Vaccination is the most effective and environmentally friendly approach to battle infectious diseases in aquaculture with minimal ecological impact and is applicable to most species of farmed fish. However, there are only 34 fish vaccines commercially available globally to date, showing the urgent need for further development of fish vaccines to manage fish health and ensure food safety. Plant genetic engineering has been utilized to produce genetically modified crops with desirable characteristics and has also been used for vaccine production, with several advantages including cost-effectiveness, safety when compared with live virus vaccines, and plants being capable of carrying out posttranslational modifications that are similar to naturally occurring systems. So far, plant-derived vaccines, antibodies, and therapeutic proteins have been produced for human and animal health. However, the development of plant-made vaccines for animals, especially fish, is still lagging behind the development of human vaccines. The present review summarizes the development of fish vaccines currently utilized and the suitability of the plant-production platform for fish vaccine and then addresses considerations regarding fish vaccine production in plants. Developing fish vaccines by way of plant biotechnology are significant for the aquaculture industry, fish health management, food safety, and human health.

INACTIVATION OF Vibrio parahaemolyticus ISOLATED FROM SEAWATER TO DEVELOP FISH VACCINE

Vibrio parahaemolyticus is a gram-negative bacterium which has been widely reported as the cause for hepatic and kidney necrosis in fishes, especially species of high economic value, in many regions across the world. Five pathogenic strains of V. parahaemolyticus were isolated from seawater samples collected in Thanh Hoa and Nghe An regions, Vietnam. All those strains were characterized by well-known morphological and biochemical characteristics of V. parahaemolyticus. Furthermore, we identified the presence of two common found virulent genes in V. parahaemolyticus (i.e. toxR và tlh) from all isolated strains while the other two genes (i.e. tdh and trh) were missing. Experimental results indicated LD50 values of isolated strains diverged from 105.73 to 107.28 on tilapia (Oreochromis niloticus) and 104.15 to 105.15 on zebrafish (Danio rerio). Then, the strain with the lowest LD50 value, named DH64.1, was selected for producing an inactivated vaccine by using formaldehyde. Consequently, the inactivated vaccine was injected on tilapia with survival rate 100% and the lack of any pathogenic symptom. Finally, vaccinated fish that were challenged with DH64.1 strain at three different challenge doses (i.e. 106, 107, 108 CFU\mL). After a 15 days post-vaccination, the relative percentage survival (RPS) of the vaccine was around 88.66-100%.

A Review of Fish Vaccine Development Strategies: Conventional Methods and Modern Biotechnological Approaches

Fish immunization has been carried out for over 50 years and is generally accepted as an effective method for preventing a wide range of bacterial and viral diseases. Vaccination efforts contribute to environmental, social, and economic sustainability in global aquaculture. Most licensed fish vaccines have traditionally been inactivated microorganisms that were formulated with adjuvants and delivered through immersion or injection routes. Live vaccines are more efficacious, as they mimic natural pathogen infection and generate a strong antibody response, thus having a greater potential to be administered via oral or immersion routes. Modern vaccine technology has targeted specific pathogen components, and vaccines developed using such approaches may include subunit, or recombinant, DNA/RNA particle vaccines. These advanced technologies have been developed globally and appear to induce greater levels of immunity than traditional fish vaccines. Advanced technologies have shown great promise for the future of aquaculture vaccines and will provide health benefits and enhanced economic potential for producers. This review describes the use of conventional aquaculture vaccines and provides an overview of current molecular approaches and strategies that are promising for new aquaculture vaccine development.