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Detection and Transmission of Renibacterium salmoninarum in Colorado Inland Trout.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Detection and Transmission of Renibacterium salmoninarum in Colorado Inland Trout./
作者:	Riepe, Tawni Brooks.
面頁冊數:	1 online resource (137 pages)
附註:	Source: Dissertations Abstracts International, Volume: 84-02, Section: B.
Contained By:	Dissertations Abstracts International84-02B.
標題:	Aquatic sciences. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=29253643click for full text (PQDT)
ISBN:	9798841783244

Detection and Transmission of Renibacterium salmoninarum in Colorado Inland Trout.
Riepe, Tawni Brooks.

Detection and Transmission of Renibacterium salmoninarum in Colorado Inland Trout. - 1 online resource (137 pages)

Source: Dissertations Abstracts International, Volume: 84-02, Section: B.

Thesis (Ph.D.)--Colorado State University, 2022.

Includes bibliographical references

Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD), is known to cause high mortality in both wild and cultured salmonids, causing concern for many of the salmonid populations. Bacterial kidney disease caused up to 80% mortality in cultured Pacific salmonids and 40% in Atlantic salmonids. Due to high mortality among salmonid species, the American Fisheries Society has defined R. salmoninarum as a regulated pathogen. Due to its regulated status, research efforts have focused on advancing fish health diagnostics and understanding the transmission of the bacteria. However, many of these studies focus on Pacific northwest salmonids and the understanding of R. salmoninarum dynamics is not well known among inland salmonids.Aquaculture propagation of Greenback Cutthroat Trout (Oncorhynchus clarkii) is a necessary component of their management. Since their protection under the Endangered Species Act, broodstock of Greenback Cutthroat Trout have been established at Colorado Parks and Wildlife (CPW) hatcheries to allow more rapid reintroduction through stocking. In 2017, hatcheries rearing isolated strains of the Greenback Cutthroat Trout contributed 1.5 million eggs during the spawning season. However, one major constraint to maintaining spawning production of the Greenback is the spread of disease within a facility. Increased contact rates between fish in raceways may influence the transmission of a pathogen. To ensure fish health and promote best practices in fish culture, fish health inspections have served as a critical step in identifying prohibitive and regulated pathogens entering or exiting the hatchery systems. Various diagnostic methods have been established to detect R. salmoninarum in salmonids. Culturing the bacteria is the most accurate and reliable assay for detection; however, it is a slow process and not suited for rapid assessment. Other methods used to detect R. salmoninarum include Direct Fluorescent Antibody Tests (DFAT), Polymerase Chain Reaction (PCR), and Enzyme-Linked Immunosorbent Assays (ELISA) and are typically performed using lethally collected kidney tissue. Currently, kidney tissues are used to screen for the presence of the bacteria using DFAT as the initial test and PCR as a confirmatory test, following the American Fisheries Fish (AFS) Health Blue Book protocol. The protocol was developed using highly susceptible Pacific northwest salmonids and it is unknown if the protocol is appropriate for testing inland salmonids which may be less susceptible. In addition, the current protocol requires sacrificing fish, which is undesirable in situations with valuable and sometimes irreplaceable broodstocks. Therefore, I examined the efficacy of the current AFS detection protocol and compared it to other potential approaches (Chapter 2). I also assessed several non-lethal approaches to detecting the bacteria (Chapter 1 and 2). In chapter 1, I compared non-lethal sampling methods with standardized lethal kidney tissue sampling that is used to detect R. salmoninarum infections in salmonids. I collected anal, buccal, and mucus swabs (non-lethal qPCR) and kidney tissue samples (lethal DFAT) from 72 adult Brook Trout (Salvelinus fontinalis) reared at the Colorado Parks and Wildlife Pitkin Brood Unit and tested each sample to assess R. salmoninarum infections. Brook Trout were used as a model species for Cutthroat Trout because they are described as highly susceptible species. Standard kidney tissue detected R. salmoninarum 1.59 times more often than mucus swabs, compared to 10.43 and 13.16 times more often than buccal or anal swabs, respectively, indicating mucus swabs were the most effective and may be a useful non-lethal method. My study highlights the potential of non-lethal mucus swabs to sample for R. salmoninarum and suggests future studies are needed to refine this technique for use in aquaculture facilities and wild populations of inland salmonids.In chapter 2, I assessed the probability of detecting the bacteria in several tissues using standard diagnostic tests. I collected three lethal tissue (kidney, liver, and spleen) and three nonlethal serum (blood, ovarian fluid, and mucus swabs) samples from 781 adult Greenback Cutthroat Trout at the Colorado Parks and Wildlife Poudre Rearing Unit. All tissues were tested for R. salmoninarum via DFAT and qPCR. The overall prevalence (all tissue types) of R. salmoninarum among the fish was 22.7% with DFAT and 81.8% with qPCR. Kidney and liver tissues resulted in the greatest number of detections using either assay. To calculate the probability of infection among kidney and liver tissues and probability of detection between assays, I developed a hierarchical occupancy model. The liver had the highest probability of infection among all fish (0.69) and the probability of detection within the liver was highest with qPCR (0.79). DFAT produced a high probability of false negative detections (0.58). Thus, I suggest that testing a combination of both kidney and liver tissues with qPCR may yield a higher detection rate that better predicts the probability of infection when performing fish health inspections.Management of R. salmoninarum is particularly difficult because the bacterium utilizes both vertical and horizontal transmission. Vertical transmission occurs when infected brood fish transmit the bacterium to their eggs and ultimate their progeny. Previous studies suggest the bacterium cannot be paternally transmitted due to limited success of bacterial entry into the egg from the spermatozoa. Thus, vertical transmission is suggested to be maternal. Horizontal transmission occurs among individuals through the ingestion of contaminated fecal matter or through direct contact with infected fish or water. In previous studies, horizontal transmission has been suggested to contribute more toward infection persistence than vertical transmission in wild and hatchery fish populations. However, the relative importance of horizontal transmission in hatcheries, where flow-through systems may expose multiple fish lots, has received little attention. I conducted experiments to determine rates of vertical and horizontal transmission.In chapter 3, I examined the potential for horizontal transmission among hatchery-reared brood fish at an R. salmoninarum-positive hatchery facility. Juvenile Cutthroat Trout were placed in sentinel cages near positive adult Rainbow Trout and Cutthroat Trout for three, 30-day periods during optimal temperatures for infection. After exposure, the caged Cutthroat Trout were euthanized, and kidney tissue was tested for R. salmoninarum with qPCR. Only one out of 360 potentially exposed fish tested positive. My data suggest that horizontal transmission may play a small role in maintaining infection in hatchery-reared inland trout. However, I also show that horizontal transmission can occur in a short time, an important consideration when moving fish both within a hatchery or from one unit to another.In chapter 4, I assessed whether the bacterium is vertically transmitted in Cutthroat Trout from the Poudre Rearing Unit in Colorado and the rate of transmission from paternal and maternal brood fish. Adult brood fish were lethally tested for R. salmoninarum and stripped of gametes to create 32 families among four R. salmoninarum infection treatments (MNFN, MNFP, MPFN, MPFP; M: male, F: female, P: positive, N: negative). Progeny from each spawning treatment were sampled at 6- and 12-month post swim-up to test for the presence of R. salmoninarum with an enzyme-linked immunosorbent assay (ELISA) and quantitative polymerase chain reaction (qPCR). My study indicates that vertical transmission occurs in inland Cutthroat trout and transmission is high when examined at the family level but is low within a family.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9798841783244Subjects--Topical Terms:

3174300
Aquatic sciences.
Subjects--Index Terms:

Bacterial kidney diseaseIndex Terms--Genre/Form:

542853
Electronic books.

Detection and Transmission of Renibacterium salmoninarum in Colorado Inland Trout.
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520 $a Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD), is known to cause high mortality in both wild and cultured salmonids, causing concern for many of the salmonid populations. Bacterial kidney disease caused up to 80% mortality in cultured Pacific salmonids and 40% in Atlantic salmonids. Due to high mortality among salmonid species, the American Fisheries Society has defined R. salmoninarum as a regulated pathogen. Due to its regulated status, research efforts have focused on advancing fish health diagnostics and understanding the transmission of the bacteria. However, many of these studies focus on Pacific northwest salmonids and the understanding of R. salmoninarum dynamics is not well known among inland salmonids.Aquaculture propagation of Greenback Cutthroat Trout (Oncorhynchus clarkii) is a necessary component of their management. Since their protection under the Endangered Species Act, broodstock of Greenback Cutthroat Trout have been established at Colorado Parks and Wildlife (CPW) hatcheries to allow more rapid reintroduction through stocking. In 2017, hatcheries rearing isolated strains of the Greenback Cutthroat Trout contributed 1.5 million eggs during the spawning season. However, one major constraint to maintaining spawning production of the Greenback is the spread of disease within a facility. Increased contact rates between fish in raceways may influence the transmission of a pathogen. To ensure fish health and promote best practices in fish culture, fish health inspections have served as a critical step in identifying prohibitive and regulated pathogens entering or exiting the hatchery systems. Various diagnostic methods have been established to detect R. salmoninarum in salmonids. Culturing the bacteria is the most accurate and reliable assay for detection; however, it is a slow process and not suited for rapid assessment. Other methods used to detect R. salmoninarum include Direct Fluorescent Antibody Tests (DFAT), Polymerase Chain Reaction (PCR), and Enzyme-Linked Immunosorbent Assays (ELISA) and are typically performed using lethally collected kidney tissue. Currently, kidney tissues are used to screen for the presence of the bacteria using DFAT as the initial test and PCR as a confirmatory test, following the American Fisheries Fish (AFS) Health Blue Book protocol. The protocol was developed using highly susceptible Pacific northwest salmonids and it is unknown if the protocol is appropriate for testing inland salmonids which may be less susceptible. In addition, the current protocol requires sacrificing fish, which is undesirable in situations with valuable and sometimes irreplaceable broodstocks. Therefore, I examined the efficacy of the current AFS detection protocol and compared it to other potential approaches (Chapter 2). I also assessed several non-lethal approaches to detecting the bacteria (Chapter 1 and 2). In chapter 1, I compared non-lethal sampling methods with standardized lethal kidney tissue sampling that is used to detect R. salmoninarum infections in salmonids. I collected anal, buccal, and mucus swabs (non-lethal qPCR) and kidney tissue samples (lethal DFAT) from 72 adult Brook Trout (Salvelinus fontinalis) reared at the Colorado Parks and Wildlife Pitkin Brood Unit and tested each sample to assess R. salmoninarum infections. Brook Trout were used as a model species for Cutthroat Trout because they are described as highly susceptible species. Standard kidney tissue detected R. salmoninarum 1.59 times more often than mucus swabs, compared to 10.43 and 13.16 times more often than buccal or anal swabs, respectively, indicating mucus swabs were the most effective and may be a useful non-lethal method. My study highlights the potential of non-lethal mucus swabs to sample for R. salmoninarum and suggests future studies are needed to refine this technique for use in aquaculture facilities and wild populations of inland salmonids.In chapter 2, I assessed the probability of detecting the bacteria in several tissues using standard diagnostic tests. I collected three lethal tissue (kidney, liver, and spleen) and three nonlethal serum (blood, ovarian fluid, and mucus swabs) samples from 781 adult Greenback Cutthroat Trout at the Colorado Parks and Wildlife Poudre Rearing Unit. All tissues were tested for R. salmoninarum via DFAT and qPCR. The overall prevalence (all tissue types) of R. salmoninarum among the fish was 22.7% with DFAT and 81.8% with qPCR. Kidney and liver tissues resulted in the greatest number of detections using either assay. To calculate the probability of infection among kidney and liver tissues and probability of detection between assays, I developed a hierarchical occupancy model. The liver had the highest probability of infection among all fish (0.69) and the probability of detection within the liver was highest with qPCR (0.79). DFAT produced a high probability of false negative detections (0.58). Thus, I suggest that testing a combination of both kidney and liver tissues with qPCR may yield a higher detection rate that better predicts the probability of infection when performing fish health inspections.Management of R. salmoninarum is particularly difficult because the bacterium utilizes both vertical and horizontal transmission. Vertical transmission occurs when infected brood fish transmit the bacterium to their eggs and ultimate their progeny. Previous studies suggest the bacterium cannot be paternally transmitted due to limited success of bacterial entry into the egg from the spermatozoa. Thus, vertical transmission is suggested to be maternal. Horizontal transmission occurs among individuals through the ingestion of contaminated fecal matter or through direct contact with infected fish or water. In previous studies, horizontal transmission has been suggested to contribute more toward infection persistence than vertical transmission in wild and hatchery fish populations. However, the relative importance of horizontal transmission in hatcheries, where flow-through systems may expose multiple fish lots, has received little attention. I conducted experiments to determine rates of vertical and horizontal transmission.In chapter 3, I examined the potential for horizontal transmission among hatchery-reared brood fish at an R. salmoninarum-positive hatchery facility. Juvenile Cutthroat Trout were placed in sentinel cages near positive adult Rainbow Trout and Cutthroat Trout for three, 30-day periods during optimal temperatures for infection. After exposure, the caged Cutthroat Trout were euthanized, and kidney tissue was tested for R. salmoninarum with qPCR. Only one out of 360 potentially exposed fish tested positive. My data suggest that horizontal transmission may play a small role in maintaining infection in hatchery-reared inland trout. However, I also show that horizontal transmission can occur in a short time, an important consideration when moving fish both within a hatchery or from one unit to another.In chapter 4, I assessed whether the bacterium is vertically transmitted in Cutthroat Trout from the Poudre Rearing Unit in Colorado and the rate of transmission from paternal and maternal brood fish. Adult brood fish were lethally tested for R. salmoninarum and stripped of gametes to create 32 families among four R. salmoninarum infection treatments (MNFN, MNFP, MPFN, MPFP; M: male, F: female, P: positive, N: negative). Progeny from each spawning treatment were sampled at 6- and 12-month post swim-up to test for the presence of R. salmoninarum with an enzyme-linked immunosorbent assay (ELISA) and quantitative polymerase chain reaction (qPCR). My study indicates that vertical transmission occurs in inland Cutthroat trout and transmission is high when examined at the family level but is low within a family.
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