Submitted to: Panamerican Congress of Veterinarian Science
Publication Type: Proceedings
Publication Acceptance Date: 4/19/2000
Publication Date: 9/11/2000
Citation: KLESIUS, P.H., EVANS, J.J., SHOEMAKER, C.A. COMMUNICABLE BACTERIAL DISEASES IN FISH FARMING: PREVENTION BY VACCINATION AND IMMUNOSTIMULATION. PanAmerican Congress of Veterinarian Science. 2000.
Technical Abstract: The impact of the communicable diseases remains as one of the major limiting factors to increased economic growth of fish farming. Among these communicable diseases are those caused by Gram- positive and -negative bacteria (Plumb, 1999). The stress on fish caused by intensive farming practices and the development of antibiotic-resistant bacteria are among the major reasons for the increased frequency of communicable bacterial disease outbreaks. In Japan, the frequent use of antibiotics has resulted in the development of resistant bacteria(Aoki,1992). In Norway, the use of vaccines against highly communicable species of Vibrio has resulted in a significant reduction in the use of antibiotics(Markestad and Graves, 1997). In the U.S., governmental regulations and the research and development costs associated with antibiotics have curtailed the introduction of new antibiotics for use by fish farmers. The best alternative method to chemical control is to prevent communicable diseases by stimulation of the fish immune system by vaccination and use of immunostimulants. Further, due to the environmental issues concerning the application of chemotherapy in fish farming, these biological control methods offer a safer and more effective means. This article presents the concepts and strategies of vaccination and immunostimulation for the prevention of highly communicable diseases in fish farming. The immune system of fish can be divided into acquired and natural immunity. Acquired immune system is mediated by antibody and memory and cytotoxic cells and natural immune system is mediated by lytic enzymes, phagocytic cells and nonspecific cytoxic cells. Vaccines stimulate the acquired immune system to produce specific antibodies and immune cells. These antibodies and cytotoxic cells act separately and in conjunction to rid the body of the communicable agent. Immunostimulants act on the natural immune system to activate its nonspecific lytic enzymes and nonspecific cytotoxic cells. These humoral enzymes and cells can act independently or together to fight the infectious agents. Activation of the acquired immune system provides long-term protection with memory and the activation of the natural immune system provides short-term protection with no memory for infectious agent. The strategic applications of vaccines and immunostimulants must include the characteristics of the target disease and of the protective immune responses, duration of protective immunity, epidemiology and the characteristics of the aquaculture system itself. For example, protection against a toxin-producing bacterium requires the use of an anti-toxin type vaccine and not the use of an immunostimulant. Antibodies must neutralize the toxin to prevent the disease. The objective of vaccination is to protect the fish before exposure to the infectious agents encountered in their production system. There is only limited numbers of licensed vaccines and most of these are for use against communicable bacterial diseases (Adams et al.,1997). Vaccine types include killed, modified live and genetic. The killed vaccine is the most common type used in aquaculture and this type of vaccine is administrated by injection. Modified live vaccine is less common, however this type of vaccine can be administered by immersion, orally administered and by injection. Genetic (DNA) vaccines are experimental and this type of vaccine is administered by injection. The choice of the type of vaccine to be used includes the characteristics of the target disease, characteristics of the protective immune response, the age of the fish, costs, safety of the vaccine and the duration of protection needed. For example,injection administration of a killed -type vaccine is expensive and used primarily in larger sized fish. Modified live vaccine is easly administered by immersion of the fish in the vaccine at