This project is curretly represented by the work of the two graduated students listed below.

Virulence Characteristics Associated with the p57 Protein of Renibacterium salmoninarum

Carolyn O'Farrell

Bacterial kidney disease (BKD) is one of the most important diseases affecting both hatchery-reared and wild salmonids worldwide. The disease is a chronic, granulomatous infection characterized by gray-white necrotic abscesses in the kidney. The causative agent of BKD, Renibacterium is a chronic, granulomatous infection characterized by gray-white necrotic abscesses in the kidney. The causative agent of BKD, Renibacterium salmoninarum, is a gram-positive diplobacillus which is a slow-growing intracellular pathogen. Despite numerous studies, little is known about the pathogen's main portal(s) of entry. Few potential virulence factors have been identified, and their roles have not been characterized. Studies have focused on one putative virulence factor which is the major soluble antigen, a 57 kilodalton protein (referred to as p57 or MSA). This protein is considered to be the cell surface immunodominant antigen, but its function has not been identified. Some isolates of R. salmoninarum with phenotypic differences in their surface components and lowered virulence have been reported, but few studies have been done on characterizing these attenuated isolates. The main objective of this study is to investigate the importance of the p57 protein to the virulence of R. salmoninarum. This will be accomplished by comparisons between the virulent isolate ATCC 33209 (wild-type) and the isolate MT239 which has attenuated virulence and lacks surface-associated p57. Molecular analyses of the msa gene (which encodes p57) will be used with both isolates to determine whether the difference in virulence can be identified genetically. The contribution of p57 will be examined in vivo with chinook salmon, Oncorhynchus tshawytscha, in a virulence challenge with both isolates to compare disease onset, progression, and mortality. Histological examination and immunohistochemical techniques will be used to investigate pathogenicity of the isolates. Furthermore, cell culture assays will be performed in vitro to compare the two isolates in host cell interactions. Achieving these objectives by these comparisons will be important in understanding the role of p57 in R. salmoninarum pathogenesis.

Genetic Diversity of IHNY in Southern Idaho Trout Aquaculture

Ryan Troyer

Viruses are important components of every ecosystem, yet few are understood from a population biology perspective. In this proposal the infectious hematopoietic necrosis virus (IHNV) will be investigated as a model system for the study of virus genetic diversity with the aim of understanding how virus populations mutate, adapt, and evolve. The work in this proposal is aimed at two major objectives which collectively investigate IHNV genetic diversity at many levels and attempt to correlate the patterns observed with possible causes. Firstly, we will characterize the genetic diversity of IHNV at three levels: within a geographic region, within host populations, and within individual fish. The geographic region to be investigated in this proposal will be a localized region of intensive trout aquaculture in south central Idaho. This region is important both as a site of high IHNV prevalence and as a novel environment for the virus. The fish host populations to be characterized will be comprised of rainbow trout from within four facilities owned by a single private producer in this region. As our second major aim, a system will be developed for inoculating fish by water-borne challenge with mixtures of IHNV strains. This system will allow us to investigate competitions between virus strains in vivo. Initially, this will allow us to measure the founder size of IHNV. Eventually, this system will provide the basic information necessary for serial passage studies of the virus in vivo under various environmental conditions.