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United States Department of Agriculture

Agricultural Research Service

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Research Project: Integrated Aquatic Animal Health Strategies

Location: Aquatic Animal Health Research

2010 Annual Report


1a.Objectives (from AD-416)
Objective 1 - Determine population and strain responses to vaccines and infectious pathogens (e.g., Edwardsiella ictaluri, Flavobacterium columnare), using genetically characterized fish. Objective 2 - Determine characteristics of coinfections and their role in disease processes in aquaculture and aquatic environments. Objective 3 - Identify microbial pathogen genes and pathways critical for host pathogenesis and immunity. Objective 4 - Develop and validate new and novel pathogen detection tests for Edwardsiella ictaluri, Flavobacterium columnare, Streptococcus iniae and S. agalactiae using genomic, proteomic, microbiological and immunological approaches.


1b.Approach (from AD-416)
Fish farmers continue to identify disease as a significant negative impact on profitability. Therefore, the goal of this project is to improve fish health and reduce this negative impact. Using a multi-disciplinary approach, we will accomplish four objectives that address important questions about bacterial diseases that affect the catfish (e.g., Edwardsiella ictaluri, Flavobacterium columnare) and tilapia (e.g., Streptococcus iniae, S. agalactiae) industries. Studies will be conducted at the gene, protein, individual, and/or population levels. Questions remain about some barriers to optimum vaccine efficacy in the field and about the responses of current and future strains of fish to pathogens and vaccines. Therefore, Objective 1 will determine population and strain responses to vaccines and infectious pathogens (e.g., E. ictaluri, F. columnare), using genetically characterized fish. In most intensive aquaculture production systems, multiple pathogens are present and result in mortality. Objective 2 will determine characteristics of coinfections and their role in disease processes in aquaculture and aquatic environments. Objective 3 will identify microbial pathogen genes and pathways critical for host pathogenesis and immunity that will provide important information for future vaccine development. Objective 4 will develop and validate new and novel pathogen detection tests for E. ictaluri, F. columnare, S. iniae and S. agalactiae so that these can be used in fish health management. The results from this work will contribute to present and future vaccine development, provide useful management information about farm use of vaccines and coinfections, and leverage development of future catfish strains being developed for the industry.


3.Progress Report
This project entitled “Integrated Aquatic Animal Health Strategies” (Project No. 6420-32000-024-00D) started in December, 2009, and is a continuation in part of research projects 6420-32000-020-00D, 6420-32000-022-00D and 6420-32000-019-00D that were terminated. Aquaculture accounts for half of the world’s fish and shellfish food supply. Fish, including catfish and tilapia, are an important source of protein worldwide and maintaining this supply will improve global food security. Fish farmers identify disease as a major problem. Disease-related losses of over 30 percent of aquaculture populations are common, and represent a significant loss of money and productivity. Scientists in Auburn, AL, will use a multidisciplinary approach to address aquatic animal diseases. Results will be used to improve production efficiency by aiding in prevention and control of disease for U.S. and world aquaculture producers.

Characterization of genes can help us to understand host immune response during vaccination. Channel catfish microarray slides were fabricated, and catfish were immunized and challenged with Edwardsiella ictaluri. Microarray analysis of catfish gene expression was carried out and at least 30 genes demonstrated significant changes after E. ictaluri vaccination and challenge. These results will improve our understanding of the catfish immune response.

To understand whether catfish bred to be resistant to enteric septicemia of catfish (ESC) are also resistant to columnaris disease, the USDA-ARS Catfish Genetics Research Unit provided six families of channel catfish. Each family was challenged with Flavobacterium columnare to determine whether they developed disease. All families developed columnaris and all had similar mortality rates.

Tilapia coinfected with Trichodina sp. and Gyrodactylus sp. were evaluated for increased disease susceptibility to Edwardsiella tarda. No differences in mortality were noted suggesting that parasites do not enhance E. tarda disease.

Streptococcus iniae was grown in tilapia to identify differentially regulated proteins and to determine virulence. Proteomic analyses and bacterial challenge studies demonstrated no differences in protein regulation and virulence between S. iniae grown in the fish and in a test tube.

To understand the increased virulence of genomovar II F. columnare isolates, we used electrophoretic approaches to identify differentially regulated proteins and carbohydrates. Analysis of proteins and lipopolysaccharides demonstrated differences within and between genomovars.

E. ictaluri flagellar genes (15) were polymerase chain reaction (PCR) amplified, expressed in Escherichia coli and compared to other enterobacteria. The recombinant proteins were confirmed by reaction to anti-His tag antibody; however, not all recombinant proteins reacted with sera from E. ictaluri infected catfish.

BioStar STREPT B Optical ImmunoAssay, commonly used for diagnosis of human Group B streptococcal (GBS) infections, was evaluated for diagnosis of GBS in tilapia. This assay identified GBS directly from swabs taken from infected fish suggesting this technique may be adapted for use in fish.


4.Accomplishments
1. Parasitized fish are more susceptible to bacterial disease. Fish health specialists had theorized that fish infected with external parasites may be more susceptible to bacterial diseases. Aeromonas hydrophila is a common pathogen of many species of farm raised fish and can result in severe economic losses to the producer and the U.S. economy. Ich is a common parasite of fish that infects both the skin and gills. Scientists at Auburn, Alabama, demonstrated that channel catfish infected with the external parasite, Ich, suffered significantly higher mortalities after coinfection with the Gram negative bacterial pathogen, Aeromonas hydrophila, than in fish infected with either Ich or Aeromonas alone. The scientists theorized that parasites damage the skin and gills, thus opening portals of easier entry for the bacterial pathogen into the fish host. The more severe mortality is the result of greater internalization of the bacterial pathogen into the fish. Better control of the parasitic infestation would result in reduction in mortalities caused by bacterial pathogens. This research will enable fish producers and health professionals to develop reliable fish health strategies and practices that prevent fish disease losses that will benefit the producer and U.S. economy.


Review Publications
Jiang, Y., Abernathy, J.W., Liu, H., Wang, S., Xu, D., Kucuktas, H., Peatman, E., Klesius, P.H., Liu, Z. 2010. Identification and characterization of matrix metalloproteinase-13 sequence structure and expression during embryogenesis and infection in channel catfish (Ictalurus punctatus). Developmental and Comparative Immunology. 34(5):590-597.

Pretto-Giordano, L.G., Muller, E.E., Klesius, P.H., Da Silva, V.G. 2009. Efficacy of an experimentally inactivated Streptococcus agalactiae vaccine in Nile tilapia (Oreochromis niloticus) reared in Brazil. Aquaculture Research [online]. Available: doi:10.1111/j.1365-2109.2009.02449.x.

Liu, H., Takano, T., Peatman, E., Abernathy, J., Wang, S., Sha, Z., Kucuktas, H., Xu, D., Klesius, P.H., Liu, Z. 2010. Molecular characterization and gene expression of the channel catfish Ferritin H subunit after bacterial infection and iron treatment. Journal of Experimental Zoology. 313A(6):359-368.

Last Modified: 8/30/2014
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