30 SEPTEMBER 2016 • WORLD AQUACULTURE • WWW.WAS.ORG has helped to formulate efficient vaccine delivery systems that protects the encapsulated antigen from the hostile gastrointestinal environment and maintain sustained release that helps to induce the immunostimulatory properties of the vaccine (Akagi et al. 2012, Kim et al. 2014). Nanoparticle systems also possess adjuvant properties that can enhance the efficacy of the antigens. An ideal vaccine carrier is expected to protect the structural integrity of the antigen and effectively deliver it to the desired mucosal surface in order to produce sufficient mucosal, humoral and cellular responses. Due to their very small size, nanoparticles enter living cells through cellular endocytosis (Treuel et al. 2013, Liang et al. 2014). Nanotechnology presents an opportunity to design particles with different composition, surface properties, shapes and sizes. Nanotechnology is the study and application of extremely small things (about 1 to 100 nanometers), and it is used across all the other science fields, such as chemistry, biology, physics, materials science, and engineering. New-generation vaccines thus produced are generally safe but they are often less immunogenic and need an adjuvant or delivery system to enhance immunity (Vinay et al. 2013). Nanoparticles can be used as adjuvants and also as delivery systems in vaccines. Nanoparticles such as dendrimers, polymeric nanoparticles, metallic nanoparticles, magnetic nanoparticles and quantum dots have emerged as effective vaccine adjuvants. Injection vaccination is very effective but not practical and economical for aquaculture species. Oral or immersion vaccines are best suited for mass vaccination. Nanotechnology can be applied to develop fish vaccines for mass vaccination – incorporated in feed or through immersion – making application of these vaccines relevant to field conditions. The use of nanotechnology in vaccinology has increased in the last decade, leading to a new field of science called nanovaccinology. Nanoparticles Nanoparticles can be grouped into several categories based on their functional properties, shape and size. Further, nanoparticle based oral delivery system are categorized as polymeric nanoparticles, inorganic nanoparticles, nanoliposomes, immunostimulating complexes, virus-like particles, and nanoemulsions. There are merits and demerits in using each of these nanoparticles for developing vaccines (Table 1). The production intensity of aquaculture production systems is increasing and this intensification is leading to increased prevalence of diseases. Poor health management in aquaculture costs roughly US$ 50 billion annually (Rather et al. 2011). In aquaculture, the possibility of occurrence of disease is unpredictable. Emerging or existing diseases may lead to severe economic losses in aquaculture. Diseases in aquaculture have a direct impact on the livelihood of millions of people as well as food security. Disease prevention is a main issue to have sustainable aquaculture. Indiscriminate use of antibiotics leads to the development of antibiotic-resistance in many bacterial species and the accumulation of antibiotics causes pollution (Karunasagar et al. 1994). Fortunately for several species in aquaculture, vaccination can provide protection against pathogens present in the water. Vaccination is one of the best health management practices in aquaculture and has helped control several major diseases in aquaculture. Historically it is based on the principle of “isolate, inactivate and inject” (Liang et al. 2014). In brief, a vaccine is a preparation of a weakened or inactivated pathogen such as a bacteria or virus or of a portion of the pathogen’s structure produced using recombinant DNA technology. Upon administration, the vaccine stimulates antibody production or cellular immunity against the pathogen but is incapable of causing severe infection, thereby reducing the risk of disease outbreak. Nanovaccines Nanovaccines are vaccines designed with a suitable nanoparticle with an antigen or group of antigens. They are emerging as a new class of vaccines that directly targets the infection site in the body by using the body’s immune system and prevents infections and diseases from spreading. Although oral vaccination is most preferred, it comes with numerous hurdles for effective delivery to immune cells. Firstly, an oral vaccine has to suffer exposure to acidic pH, proteolytic enzymes and bile salts, leading to its degradation in the gastrointestinal tract. Encapsulating antigenic materials using several polymeric and lipid-based nanoparticle carriers could be an effective approach because such particles can reduce degradation of antigens in the GI system (Nirmal et al. 2014). Nanotechnology Nanovaccines: a Possible Solution for Mass Vaccination in Aquaculture T.N. Vinay, G.C. Tanmoy, P. Anutosh, K.G. Sanjay and S. Biplab Nanotechnology has helped to formulate efficient vaccine delivery systems that protect the encapsulated antigen from the hostile gastrointestinal environment and maintain sustained release that helps to induce the immunostimulatory properties of the vaccine. Nanoparticles can be used as adjuvants and delivery systems in vaccines. Nanotechnology can be applied to develop fish vaccines for mass vaccination — incorporated in feed or through immersion — making application of these vaccines relevant to field conditions.
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