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ARS Home » Southeast Area » Auburn, Alabama » Aquatic Animal Health Research » Research » Research Project #426749

Research Project: Pathogen Characterization, Host Immune Response and Development of Strategies to Reduce Losses to Disease in Aquaculture

Location: Aquatic Animal Health Research

Project Number: 6010-32000-026-00-D
Project Type: In-House Appropriated

Start Date: Apr 28, 2015
End Date: Apr 27, 2020

Objective 1: Identify and characterize genetic diversity, mechanisms of pathogenesis and virulence factors in Flavobacterium (F.) columnare. Subobjective 1.A.: Comparative bacterial genome analysis of Flavobacterium columnare isolates of different genetic types and virulence. Subobjective 1.B.: Molecular basis of lipopolysaccharide (LPS) and capsular polysaccharide (CPS) antigenic diversity in Flavobacterium columnare. Subobjective 1.C.: Characterize the growth and survival of F. columnare in fish mucus. Objective 2: Develop vaccines and probiotics that provide protection against bacterial and parasitic pathogens and identify mechanisms of immunity by identifying and characterizing host mechanisms responding to infection and host-pathogen interactions that can be used to develop approaches that reduce losses to disease. Subobjective 2.A.: Chemical mutagenesis of Flavobacterium columnare to modify the capsular polysaccharide (CPS) to develop attenuated vaccines. Subobjective 2.B.: Evaluate the protective effect of a DNA vaccine encoding Ich immobilization antigens to protect catfish against Ich. Subobjective 2.C.: Develop a waterborne challenge model and recombinant protein vaccine to protect channel catfish against virulent Aeromonas hydrophila.

Catfish and tilapia farmers continue to identify disease as a major problem in their industries. For instance, columnaris disease, caused by Flavobacterium (F.) columnare, is one of the top two diseases diagnosed in the industry. Since 2009, a virulent strain of Aeromonas (A.) hydrophila has greatly impacted the catfish industry and resulted in losses of greater than 12 million U.S. dollars. Ichthyophthirius (I.) multifiliis, the parasite that causes Ich, is responsible for annual losses of 1.2 million U.S. dollars to the catfish industry alone. An increased understanding of the pathogen, host responses to the pathogen, and host-pathogen interactions is necessary for disease prevention and control. This in-house project will expand our knowledge of these and will use new and existing knowledge to develop approaches to reduce disease losses in catfish and tilapia aquaculture. Development of disease prevention strategies will increase the profitability and sustainability of these important aquaculture industries. Objective 1 recognizes that although columnaris disease has been intensely studied in the past, important questions concerning genetic diversity of isolates impacting aquaculture and mechanisms of pathogenesis have newly emerged. A greater understanding of these factors will enhance our ability to improve existing and develop new prevention strategies practical for use in the catfish and tilapia industries. Research conducted in this objective will utilize comparative genome analyses to identify genetic similarities and differences among F. columnare isolates of different genomovars (genetic types) and will correlate the genetic differences with variation in virulence. The genome sequences will be exploited to determine the molecular basis of lipopolysaccharide and capsular polysaccharide antigenic diversity in F. columnare. The growth of F. columnare in catfish mucus will be used as a model to determine the proteomic changes that occur in F. columnare during the colonization of catfish and how these changes are involved in virulence. Objective 2 acknowledges that even though there is a commercially available vaccine for F. columnare and experimental vaccines exist for other bacterial and parasite pathogens, there is a need to develop improved disease prevention methods and identify the mechanisms responsible for protective immunity. Research conducted will utilize chemical mutagenesis to modify the capsular polysaccharide of F. columnare to develop more effective attenuated vaccines. A DNA vaccine for I. multifiliis will be developed based on proteins of the parasite that have been previously demonstrated to be protective. A reproducible waterborne challenge model for virulent A. hydrophila will be developed and will allow for more effective testing of treatment or prevention strategies. A recombinant protein vaccine for A. hydrophila will be developed based on secreted proteins of the bacterium that are identified as protective. This research will increase our understanding of the host immune responses against pathogens and will develop improved and new vaccines for prevention of disease in catfish and tilapia aquaculture.