Recipient Organization
WASHINGTON STATE UNIVERSITY
240 FRENCH ADMINISTRATION BLDG
PULLMAN,WA 99164-0001
Performing Department
ANIMAL HEALTH RESEARCH CENTER
Non Technical Summary
Strawberry Disease is a significant economic concern for the trout aquaculture industry, but at this time no one has conclusively identified the etiologic agent. The purpose of this project is to apply microbiological, imaging and molecular tools to identify the etiologic agent of strawberry disease in rainbow trout. Once we have identified an agent or other cause, it should be possible to develop remedies for the industry.
Animal Health Component
15%
Research Effort Categories
Basic
80%
Applied
15%
Developmental
5%
Goals / Objectives
Strawberry disease (SD) is a subchronic, non-debilitating skin disorder that affects rainbow trout (Oncorhynchus mykiss). Manifestations include yellow or red non-raised or slightly raised inflammatory lesions that are heavily infiltrated with lymphocytes and to a lesser extent with macrophages. The condition is self-limiting (c.a. 8 weeks) and fish experiencing SD do not lose weight or change their behavior. The disease was first recognized in Washington State in the 1950s, but no etiologic agent has been identified. From a producer perspective, the primary problem with SD is that is occurs on market sized fish (>90 g) and while this does not impact fish health it does result in product downgrade or rejection (nobody wants a fillet with a lesion). Incidence rates have been reported as high as 80% in the U.K. and 50% in southern Idaho; thus, the economic impact can be substantial. The condition responds to treatment by oxytetracycline and there are reports of limited
success in experimental transmission. Consequently, we hypothesize that SD is caused by an infectious agent. We developed preliminary 16S rRNA libraries to describe the bacterial community within lesions and normal trout skin. This work found evidence of a unique bacterium associated with SD lesions. We are currently generating additional libraries as well as documenting other parameters (bacteriology, virology, electron microscopy, and histology). The present application will extend this work to include additional field sampling, cell culture for agent isolation, experimental fish inoculation, and a broader survey of the distribution of putative agents amongst normal and diseased tissues. The specific objectives of the current and proposed research are: 1. Determine bacterial community composition within lesions using conventional culture and non-culture-based methods. 2. Use a cell culture model for isolation of the infectious agent(s). 3. Determine the feasibility of a challenge
model for SD. 4. Determine the prevalence of agent from a survey of trout with and without SD lesions. If we are successful in identifying putative infectious agent(s) from this work, we will endeavor to satisfy the Henle-Koch postulates for causation to finally resolve the etiology of SD. Knowing the agent that produces SD is the first step to developing more effective control measures. This work is part of a aquaculture research focus within the labs of all of the investigators listed below.
Project Methods
Objective 1 includes construction and analysis of 16S libraries (10 completed) from fish lesions and healthy tissues (each collected from the same fish). We are also using conventional bacteriology and virology to screen lesion samples and extensive examination of both histology and trasmission electron microscopy to find evidence of disease agents. To date we have identified one putative agent and developed a nested-PCR assay for this agent. Initial work under objective 2 involved two salmonid fish lines, but we plan to add a third line for testing in fall 2007. The third objective will proceed using conventional fish challenge facilities and lesion homogenate as innoculum (isolated material will be used if objective 2 is successful). The final objective will rely upon PCR to test for the presence of any putative agents in both SD lesions and other lesions found at a trout processing plant.