Application of DNA vaccine technology to aquaculture

The aquaculture industry needs to augment its global production and efficie ncy to meet the increasing consumer needs for fish and shellfish products. Unfortunately, infectious diseases have been a major impediment to the deve lopment and profitability of fish farms. While vaccines offer the most effi cient way to control infectious pathogens, current products have only been successful against some diseases. These are mostly bacterial, and there are still several important diseases, mainly of viral and parasitic origin, fo r which no prophylactic treatment exists. DNA vaccines, compared to traditi onal antigen vaccines, have several practical and immunological advantages that make them very attractive for the aquaculture industry. The early succ ess of DNA vaccines in animal models was very encouraging, but fish are uni que in many aspects, and findings with other classes of vertebrate, namely mammals and birds, do not necessarily apply to aquatic animals. However, mo re recent studies with reporter genes showed that fish cells efficiently ex press foreign proteins encoded by eukaryotic expression vectors. A piscine- specific backbone vector might eventually improve immune responses to DNA v accines, but there is already strong direct evidence for the induction of p rotective immunity with currently available plasmids. Immune responses to p lasmid DNA injected intramuscularly (IM) into fish are characterized by the production of antibodies, which have been shown to be neutralizing in two different viral disease models. There is also indirect evidence suggesting the induction or cell-mediated immunity. Despite this evidence, immune resp onses to DNA vaccines have only been poorly characterized in fish because o f the limited knowledge of the piscine immune system, and the small number of studies on the subject. Apart from optimizing the efficiency of DNA vacc ines, other important issues, such as safety and production cost will be de terminants for the potential application of this technology in commercial f ish farms. Alternative methods of administration will also have to be devel oped for small fish and low-valued species, for which IM injection is not p ractical and/or cost effective. (C) 2000 Elsevier Science B.V. All rights r eserved.