Graduate Thesis Or Dissertation
 

The isolation, comparison, and attenuation of several viruses infecting Oregon salmonids

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sj1395638

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  • The Oregon strain of the agent of infectious hematopoietic necrosis (IHN) was isolated from fingerling sockeye salmon (Oncorhynchus nerka) by J. L. Fryer in 1958. Before the study reported herein no other virus had been recovered from any fish population in Oregon. Therefore, in July, 1971 a survey was initiated to determine the status of viral infections in various populations of Oregon salmonids. Stocks tested represented several of the state's major watersheds, coastal streams, brood fish from selected hatcheries, and private lakes and ponds. Three viruses were isolated during the survey. IHN virus was recovered from rainbow trout (Salmo gairdneri) displaying typical symptoms of that disease and infectious pancreatic necrosis (IPN) virus was isolated from asymptomatic cutthroat trout (S. clarki) and coho salmon (O. kisutch). Serum neutralization tests indicated that fall chinook salmon (O. tshawytscha) had been exposed to IPN virus although they were not infected at the time of examination. Host range studies were performed with the three agents by adding them to aquaria water containing fry of several species. IHN virus caused fatal infection in both kokanee salmon (landlocked 0. nerka) and rainbow trout at 49 and 54°F although kokanee appeared more susceptible than rainbow trout. The coho IPN isolate (Coho- IPN) was lethal only for coho fry and only at 59°F while the cutthroat trout isolate (CTT-IPN) was not virulent for any of the species tested including cutthroat trout. None of the three viruses were capable of infecting any of several species of non-salmonids under prevailing test conditions. Coho-IPN and CTT-IPN were compared to each other and to VR-299, a reference strain of IPN virus, with respect to their antigenic compositions. No antigens unique to only one of the three strains were detected by immunodiffusion or immunoelectrophoretic methods although three separate viral antigens were identified for each agent. Cross-plaque neutralization and comparisons of susceptibility to freezing and thawing showed that the two western isolates were much more closely related to one another than to VR-299. Attempts were made to attenuate the IHN and both IPN strains recovered during the survey as an initial step towards developing live virus vaccines against those agents. Those viruses were serially passaged on turtle heart, human epidermoid larynx carcinoma, and steelhead trout embryo cell lines at temperatures ranging from 4 to 37°C. Comparisons of virulence for susceptible fry were made between passaged and wild type viruses. IHN virus passed 41 times on a steelhead trout cell line (STE-137) at 18°C showed a reduction in virulence for kokanee salmon of at least 4 x 107-fold when added to aquaria water. That attenuated strain protected 15 of 18 vaccinated fry against an intraperitoneally injected challenge equivalent to 42 x LD₅₀ for the wild type agent. A 38-fold reduction in virulence of CTT-IPN for coho salmon fry was achieved by passing that virus 93 times at 18°C on STE-137 cells. Eleven of 13 of those fish vaccinated with an ip injection of 13 plaque forming units of the attenuated strain survived a challenge dose of the wild type virus equivalent to 860 x LD₅₀. The results obtained by propagating the three isolated agents on other cell lines, at other temperatures, and subjecting them to varying numbers of passages are reported.
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  • File scanned at 300 ppi (Monochrome, 256 Grayscale) using Capture Perfect 3.0.82 on a Canon DR-9080C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
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