Oral vaccination for sustainable disease prevention in aquaculture—an encapsulation approach

Abstract

The prevalence of infectious diseases in the aquaculture industry and a limited number of safe and effective oral vaccines has imposed a challenge not only for fish immunity but also a threat to human health. The availability of fish oral vaccines has expanded recently, but little is known about how well they work and how they affect the immune system. The unsatisfactory efficacy of existing oral vaccinations is partly attributable to the antigen degradation in the adverse gastrointestinal environment of fishes, the highly tolerogenic gut environment, and inferior vaccine formulation. To overcome such challenges in designing: an easier, cost-efficient, and effective vaccination method, several encapsulation methods are being adopted to safeguard antigens from the intestinal atmosphere for their immunogenic functions. Oral vaccination is easily degraded by gastric acids and enzymes before reaching the immunological site; however, this issue can be solved by encapsulating antigens in poly-biodegradable nanoparticles, transgenic designed bacteria, plant systems, and live feeds. To enhance the immunological impact, each antigen delivery method operates at a different level. Utilizing nanotechnology, it has been possible to regulate vaccination parameters, target particular cells, and lower the antigen dosage with potent nanomaterials such as chitosan, poly D,L-lactic-co-glycolic acid (PLGA) as vaccine carriers. Live feeds such as Artemia salina can be utilized as bio-carrier, owing to their appropriate size and non-filter feed system, through a process called bio-encapsulation. It ensures the protection of antigens over the fish intestine and ensures complete uptake by immune cells in the hindgut for increased immune response. This review comprises recent advances in oral vaccination in aquaculture in terms of an encapsulation approach that can aid in future research.

Recent development of oral vaccines (Review)

“…The effectiveness of their adjuvant activity in preventing reinfection, generating serum and mucosal immune responses and establishing long-lasting immune memory is noteworthy ( 96 ). However, further understanding and control of the toxicity of oral attenuated live vaccines is imperative, as numerous studies are currently only focused on animal experimentation ( 97 , 98 ).…”

Transforming Aquaculture Through Vaccination: A Review on Recent Developments and Milestones

“…In practice, this minimizes the cost of intensive labor and alleviates animals of stress or trauma, protecting the overall welfare and wellbeing of the organisms reared. In addition, it enables the vaccination of animals of any size, leaving space for a wide range of applications, including the vaccination of fish fry that are often in urgent need of immunization [10,16,78,82,87,95,96].…”

“…The integrity of vaccine antigens is paramount to this method of administration, as oral vaccines need to be capable of overcoming both the aquatic and the harsh environment of the animal's digestive tract. The degradation of antigens by low pH values and proteolytic enzymes constitutes an important hurdle to the consistent uptake of oral vaccines, hence adding an additional layer of difficulty to the implementation of oral vaccination in aquaculture settings [96][97][98]. Furthermore, the unpredictable feeding behavior of many species can potentially undermine the consistent and accurate uptake of oral vaccines, eventually restricting this route of administration to mainly booster vaccination applications as of now [73].…”

“…To optimize the uptake of oral aquaculture vaccines and induce stronger and longer-lasting immunization, many innovations have emerged, with particular emphasis being placed on encapsulation techniques to address the vulnerable integrity of oral vaccine antigens [96,100]. This has proven quite a verdant field for scientific and technological exploration, as many variables that influence the effectiveness of this approach require elucidation to have a comprehensive grasp on the intricacies that lead to adequate immunization [18].…”

“…Oral vaccination still holds the reins as the most attractive route of vaccine administration in the aquaculture sector. To address the challenges that are typically associated with the application of this method, concerning the integrity and availability of vaccine antigens inside the harsh conditions of the gastrointestinal tract and the aquatic environment of fish, encapsulation has emerged as a predominant technology in the production of effective oral vaccines in the industry of aquaculture [96]. Typically, this approach encompasses the utilization of polymers, which are either natural or synthetic in nature.…”