2012 Annual Report
1a.Objectives (from AD-416):
Selective breeding for increased disease resistance is a powerful tool to complement animal health control strategies in the prevention of devastating disease. Through selective breeding over 3 generations, we (NCCCWA) have increased resistance to the bacterial cold water disease agent, Flavobacterium psychrophilum in RBT. Preliminary field testing indicates superior survival and on-farm performance with this selected RBT stock at sites experiencing endemic disease. Interestingly, this selection has also resulted in a significant increase in spleen size and alterations of the in vitro immune response profiles among the resistant fish. Thus, the overall impact of this selective breeding may have also significantly affected both innate and adaptive immune functions.
1b.Approach (from AD-416):
Our approach utilizes pedigreed rainbow trout lines, bred for differences in survival following laboratory challenge with the Fp strain, CSF259-93. This selection process has also led to increased spleen size in resistant fish and unique leukocyte response profiles to in vitro challenge with Fp LPS. The first objective will employ a panel of genome-sequenced Fp strains and other Gram-negative salmonid pathogens to probe the specificity of the induced resistance. Our extensive genomic analysis of Fp virulence variants will facilitate characterization of potential broad-based resistance. The second objective will dissect the cellular and molecular bases of this genetic resistance. Differential effects on cytokine and antibody production in critical immune tissues, including the spleen, will be determined. The third objective will address the impact of this selective breeding on immunoprophylaxis elicited by vaccination with homologous and heterologous Fp strains, as well as other bacterial pathogens.
This project was initiated on Jan 15th 2012 and is a multi-institutional, collaborative effort between the NCCCWA, the Virginia Institute of Marine Science, and the College of William and Mary. During the reporting period, we have made progress on objectives 1 and 2. The NCCCWA breeding program provided to collaborators three genetic lines of rainbow trout that have varying resistance to bacterial cold water disease. These lines are designated ARS-Fp-R (resistant), ARS-Fp-C (control) and ARS-Fp-S (susceptible). As part of Objective 1, we examined whether the ARS-Fp-R line has broad resistance to challenge with bacterial pathogens by comparing the survival to the selection control lines ARS-Fp-C and ARS-Fp-S. This year, bath and injection challenge experiments were completed using Yersinia ruckeri biotype 1 and Flavobacterium columnare as well as selected variants of F. psychrophilum. Analyses of the challenge results and correlation with specific disease pathology are underway. During the summer of 2012, two undergraduates from the College of William and Mary interned at the NCCCWA over a 10 week training period. Experiments were completed that involved measuring immune cell populations isolated from different trout tissues and differences were compared between genetic lines both before and after challenge with F. psychrophilum.