Current scenario of fish vaccines

Prevention and control of fish diseases is a high priority in aquaculture industry. The therapeutics for control of piscine diseases is meagre, control of diseases in aquaculture and fish farms relies on a combination of good management practices, use of the few approved and commercially available drugs and vaccines. The vaccination process differs depending upon fish species and temperature. The vaccination process must be performed within minimal period before the fishes get pathogenic exposure. In addition to temperature, stress can induce immune suppression and be limiting factors for vaccine efficacy. Fish are commonly immunized by three procedures: intra-peritoneal injection (IP), immersion in a diluted vaccine solution (short or long bath) or oral administration of the vaccine. These methods have different merits and demerits with respect to the level of protection. The injection and immersion routes provides enough protection to fish immunization in commercial production. For oral vaccination, the research is focused on protecting the antigens released during the process of digestion and decomposition in the stomach and anterior part of the gut. However, the use of encapsulated antigens in alginate or polylactic glycolic acid microparticles provide promising results.

Economically, oral vaccination (one or more booster immunizations) is the ideal route to be employed in a vaccination platform. Polyvalent vaccines, for salmonids incorporating different Vibrio species and A. salmonicida as an antigens are available. Research was conducted for use of DNA vaccines as safe live vaccines which shows higher level of accomplishment against Furunculosis. But their approval for use in the field has not yet been forthcoming. Although there are a great number of commercial Vibrio anguillarum vaccines, the majority of them includes in their formulations only O1, or combination of serotypes O1 and O2a.

However, various polyvalent oil-adjuvanted vaccines, including several combinations of Vibrio anguillarum with other pathogens, such as V. ordalii, V. salmonicida, A. salmonicida, Moritella viscose and Infectious Pancreatic Necrosis Virus (IPNV), are also available in the market to be used for salmonids by the intra-peritoneal route. Recently, an attenuated O-antigen deficient Edwardsiella ictaluri strain has been developed which was safe and provided high long-lasting acquired immunity (for at least 4 months) following a single bath immersion in 9-14 days old channel catfish without booster dose. Since 2000, this improved live E. ictaluri vaccine has been produced , by Intervet Inc., under the trade name AQUAVAC-ESCO. It constitutes, the first licensed bacterial live vaccine in aquaculture formulated with an attenuated pathogenic strain. Vaccines against Yersiniosis as formalin inactivated whole cell cultures of Y. Ruckeri serovar I, Biotype 1 (Hagerman strain) are also commercialized. Lately, a commercial aqueous live vaccine developed by Novartis has been licensed under the name of “Renogen” for prevention of Bacterial Kidney Disease (BKD) .

Several other vaccines for different bacterial pathogens are listed below:

Vaccines for viral diseases like IPNV, IHNV (Infectious Hematopoietic Necrosis Virus), Salmon pancreas disease, ISA (Infectious salmon anemia), Nodaviral diseases; SVC (Spring viremia of carp) and KHV (Koi Herpes virus disease) are also commercially accessible. Currently existing vaccines are based on simple empirically established inactivated pathogens. A few recombinant subunit vaccines and DNA vaccines are also available. Limited knowledge on piscine immune systems limits the expansion of vaccines. Vaccines against intracellular bacterial and viral pathogens are one of the gigantic challenges in forthcoming years. New vaccination strategies, aquaculture expansion and disease investigation centers should be initiated. Strong coordination should be created between pharmaceutical companies and academic research for a better improvement of live fish vaccines.