Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2008
Publication Date: 8/4/2009
Citation: Shoemaker, C.A., Klesius, P.H., Arias, C.R., Evans, J.J. 2009. Use of Modified Live Vaccines in Aquaculture. Journal of the World Aquaculture Society. 40(5):573-585. Interpretive Summary: Vaccination is an important disease management strategy used to maintain human and animal health worldwide. Vaccines developed for aquaculture have reduced antibiotic use in fish production. Original fish vaccines were bacterins (formalin killed bacteria) delivered by immersion or injection that induced humoral (antibody) immunity. Next generation vaccines relied on multiple killed antigens delivered with an adjuvant to enhance vaccine effectiveness. Work in the 1990's demonstrated the use of various strategies to develop modified live vaccines for use in fish. A modified live vaccines ia a live pathogen that has been rendered non-pathogenic or avirulent by physical, chemical or genetic engineering methods. The modified live vaccine typically retains its ability to cellular immunity. Modified live vaccines are advantageous in that they can be easily delivered (i.e., by immersion in young fish) and stimulate both humoral and cellular immunity of long duration. Disadvantages include issues with modified live vaccine safety to the host and environment. A successful modified live vaccine for use in warm water aquaculture is used to highlight the live vaccine strategy.
Technical Abstract: Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish (ESC), is responsible for $60 million in annual losses to the channel catfish industry. Development of a successful vaccine against ESC required the vaccine to be safe and easily administered to young fish. Further, the vaccine needed to stimulate protective cell mediated immunity of long duration. We developed a modified E. ictaluri isolate (RE-33) that was attenuated and did not cause disease in susceptible fish. In vivo reversion to virulence studies demonstrated the vaccine was safe. Safety on commercial farms was demonstrated in over 2.2 million catfish (Ictalurus punctatus) in State veterinarian (Alabama and Mississippi) and United States Department of Agriculture-Animal Plant Health Inspection Service approved field trials in 1997. Efficacy was also shown to a number of E. ictaluri field isolates in laboratory trials involving 3-9 month old catfish. In 1998-99 we demonstrated the effectiveness of the vaccine in 7 to 10 days post hatch fry following immersion. Vaccination of eyed eggs (in ovo) was recently accomplished (1999, 2000). Intervet Inc., (Millsboro, Delaware) licensed, produced and marketed the modified live E. ictaluri RE-33 in 2000, 2001 and 2002 under the trade name AQUAVAC-ESC'. This past year, we further characterized the E. ictaluri vaccine mutant. Immunoblot analysis of the LPS (lipopolysaccharide) demonstrated the vaccine mutant lacked high molecular weight bands in the LPS as compared to the parent isolate. Further characterization demonstrated that two fingerprinting techniques (MIDI's fatty acid methyl esters and BIOLOG's carbon utilization profile) were able to discriminate between the parent and mutant E. ictaluri. AQUAVAC-ESC' is being successfully marketed and about 25 % of all channel catfish fry produced in the U.S. were immunized in 2002.