Michigan state university - aquatic animal health lab
Michigan state university - aquatic animal health lab
Dr. Tom Loch
Nisha Shrestha1,2, Myron Kebus3, Sean Lennox1,2, Megan Shavalier1,2, Christopher Knupp1,2, Fabiana Pilarski1,3, Matthew Smith4, Nicholas Phelps5, Thomas Loch1,2,3,6
1Michigan State University - Aquatic Animal Health Laboratory, Aquatic Animal Disease Ecology Program; 2Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University; 3Dept. of Pathobiology & Diagnostic Investigation, College of Veterinary Medicine, Michigan State University; 4Analytics, Xylem/YSI; 5Aquatic Invasive Species Research Center, University of Minnesota; 6Department of Comparative and Integrative Biology, Michigan State University
Flavobacterium psychrophilum, causative agent of bacterial coldwater disease (BCWD) and rainbow trout fry syndrome, is a primary disease impediment to trout and salmon (Family Salmonidae) aquaculture globally. In the USA, BCWD outbreaks occur perennially, including within aquaculture facilities and hatcheries of the North Central Region (NCR). Although a range of BCWD prevention and control measures are available, their efficacy is often inconsistent. One possible factor contributing to treatment inconsistency is the intraspecific geno- and sero-diversity of F. psychrophilum that has become increasingly apparent in some regions of the USA and abroad. Unfortunately, most of the F. psychrophilum variants causing losses in NCR trout and salmon farms have not been identified, with likely implications for effective vaccination approaches. Within a larger study aiming to enhance US farmed fish health, efforts to isolate, identify, and characterize F. psychrophilum variants in NCR trout and salmon facilities were undertaken. Clinical examinations and bacteriological analyses were completed for 225 moribund salmonids from ten facilities in nine NCR states (e.g., Michigan, Ohio, Iowa, Wisconsin, Minnesota, Missouri, Illinois, Indiana, and South Dakota), resulting in the recovery of 259 yellow-pigmented bacterial isolates from 934 primary cultures. Among these, the majority (n=133) were identified as F. psychrophilum via specific endpoint PCR analyses, revealing an infection prevalence of ~45% across the seven facilities where F. psychrophilum was recovered. Genotyping and serotyping (n=90 F. psychrophilum isolates) via multilocus sequence typing (MLST) and multiplex PCR, respectively, revealed nine sequence types and all five currently recognized molecular serotypes. Among the nine recovered sequence types, five were novel, and one had previously been exclusively reported from Norway, thus marking its first detection in the USA. Notably, most F. psychrophilum isolates from 5/7 states belonged to clonal complex CC-ST10, which has been widely detected and associated with BCWD outbreaks in the USA and abroad. Interestingly, the CC-ST10 isolates varied in molecular serotype, belonging to Type-1, Type-2, and Type-3. Guided by the results to date, a range of F. psychrophilum geno- and sero-variants have been selected for growth kinetics and in vivo virulence experiments. Subsequently, the next study phase will evaluate the protective efficacy of multiple autogenous bacterin preparations aimed at enhancing fish health and productivity in the NCR.
1,2Sean M. G. Lennox, 1,2,3Thomas P. Loch
1Michigan State University - Aquatic Animal Health Laboratory, 1129 Farm Lane, Room 340J, Food Safety and Toxicology Building, Michigan State University, East Lansing, MI 48824; 2Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University; 3Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University.
Within the U.S.A., federal authorities maintain “reportable” aquatic animal pathogen lists that detail reporting requirements, mandatory actions, and/or recommendations following the detection or suspicion of listed pathogens. Oftentimes, state authorities also maintain “reportable” aquatic animal pathogen lists, which are frequently determined by individual entities and without a central repository, thereby potentially leading to a lack of clarity on reporting requirements that may vary across states. To this end, and as part of a semester-long undergraduate student research project in 2020, lists of “reportable” finfish pathogens (defined here as finfish pathogens deemed to be of regulatory significance by an entity that may have requirements to notify a relevant authority upon detection) were collected from as many U.S. states as possible (n=47). This information was collected from state and federal websites, state administrative code, and via direct correspondence with state veterinarians and fish health authorities. In addition, pathogen lists maintained by some regional fish health organizations (e.g., the Great Lakes Fish Health Committee and Northeast Fish Health Committee) were also collected. State and regional lists were also compared to the National List of Reportable Animal Diseases (NLRAD) proposed in 2020 and maintained by the U.S. Department of Agriculture Animal and Plant Health Inspection Service, as well as the World Organisation for Animal Health (WOAH) “listed diseases.” Some states were found to maintain a list seemingly tailored to their own needs, whereas others referenced lists maintained by external organizations. Rarely, some states were found to not have formal lists. Although not necessarily exhaustive, this compilation of U.S. “reportable” finfish pathogens revealed multiple interesting trends, including the most and least frequently listed pathogens by state that were not WOAH or NLRAD listed; for example, Myxobolus cerebralis and infectious pancreatic necrosis virus are considered “reportable” by 25 and 24 states, respectively, despite not being NLRAD or WOAH-listed. Additional observations will also be discussed, but this initial delve into finfish pathogen reportability in the U.S.A. elucidates some of the extensive state-to-state variability and highlights the value of creating/maintaining a central, contemporary “reportable” pathogen repository into the future.
1,2Brady J. Yokom, 1,2Sean M.G. Lennox, 1,2Nisha Shrestha, 1,2Courtney E. Harrison,
2,4Travis O. Brenden, 2,4Mark P. Ebener, 1,2,3,5Thomas P. Loch
1Michigan State University – Aquatic Animal Health Laboratory, Aquatic Animal Disease Ecology Program, 1129 Farm Lane, Room 340G, East Lansing MI, 48823; 2Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University, 480 Wilson Road, East Lansing MI, 48824; 3Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, 784 Wilson Road, Room G-100, East Lansing MI, 48823; 4Quantitative Fisheries Center, Michigan State University, 375 Wilson Road, Room 101, East Lansing MI, 48824; 5Department of Comparative Medicine and Integrative Biology, Michigan State University, 784 Wilson Road, Room G-100, East Lansing MI, 48823
Lake whitefish (Coregonus clupeaformis; Family Salmonidae) comprise a culturally, ecologically, and economically invaluable fishery in the Great Lakes. Concerningly, Great Lakes lake whitefish (GL-LWF) continue to suffer from poor recruitment for multiple hypothesized reasons; however, any potential role infectious disease may be playing in these declines remains largely unknown. Among the fish pathogens previously detected in GL-LWF at a relatively high prevalence is Renibacterium salmoninarum (Rs), which causes bacterial kidney disease (BKD) in other salmonids and is known to readily transmit from parents to offspring via infected eggs and reproductive fluids. To date, the capacity of Rs to cause BKD and/or mortality in GL-LWF has never been assessed despite detections in naturally infected fish. To this end, the in vivo virulence of Rs to GL-LWF was assessed under controlled laboratory conditions. Laboratory-reared GL-LWF (~28-months old) were immersion-exposed to one of five concentrations (n=4-5 fish/concentration, in triplicate) of Rs (isolate 221012-1-26F; 1.7 x 102 – 1.7 x 106 colony forming units/ml), after which disease progression and cumulative percent mortality were monitored for 90 days. Initial external disease signs in Rs-exposed GL-LWF included scale loss, and dermal swelling and hemorrhage, followed by subsequent development of multiple additional gross disease signs, including in some cases, severe renal granulomatous-type lesions characteristic of BKD. Cumulative mortality in Rs-exposed GL-LWF treatments ranged from 26.6% to 100%, compared to 13.3% in mock-exposed fish. Using an enzyme-linked immunosorbent assay (ELISA), Rs-specific antigen was detected in kidney/spleen/heart tissue homogenates of fish at all but the lowest exposure concentration. Additionally, cultures on modified kidney disease medium yielded Rs–suspect bacterial growth from the kidney tissues of fish within the three highest Rs exposure treatments. Using an Rs-specific quantitative PCR, representative bacterial isolates were, in all cases, confirmed as R. salmoninarum. In contrast, Rs was not detected in any mock-exposed fish via culture or ELISA. Collectively, study findings provide evidence that Rs is capable of initiating systemic infections and causing subsequent disease and mortality in GL-LWF.