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Epidemiology of Fish and Wildlife Diseases
Fish

Samples of genetics and genomics research from the USGS Ecosystems Mission Area about the epidemiology of fish diseases.

Salmon with clinical signs of Bacterial Kidney Disease (BKD). Photo credit: USGS Western Fisheries Research Center Sequence analysis of new isolates of IHNV Northern snakehead (Channa argus). Photo credit: USGS, courtesy USGS Southeast Ecological Science Center Photo Gallery Yellow color shows thiamine degradation on an agar plate of P. thiaminolyticus strain 8120. Photo credit: Catherine A. Richter, Columbia Environmental Research Center. Great Lakes. Photo credit: Jeff Schmaltz/NASA
Adaptation to Bacterial Kidney Disease
(Purcell, Elliott)
Emerging Virus Threat to Fish in Western Washington (Kurath) Northern Snakehead: Risk of Exotic Pathogen Introduction (Iwanowicz, Densmore) Q-PCR Detection of Bacterial Sources of Thiaminase I (Richter) Viral Hemorrhagic Septicemia Virus in the Great Lakes
(Winton)

Adaptive Potential of Chinook Salmon to Resist Bacterial Kidney Disease (BKD)

Salmon with clinical signs of Bacterial Kidney Disease (BKD). Photo credit: USGS Western Fisheries Research Center
Salmon with clinical signs of Bacterial Kidney Disease (BKD). Photo credit: USGS Western Fisheries Research Center

Mass mortality events due to infectious disease agents in wild fish populations are troubling, but it is the long-term, population-level consequences which may be of more significance. Basic evolutionary theory predicts that populations with sufficient genetic variation will adapt in response to pathogen pressure. Chinook salmon were introduced into Lake Michigan in the late 1960s from a Puget Sound population (Washington State). In the late 1980s, collapse of the forage base in Lake Michigan was thought to contribute to die-offs of Chinook salmon due to Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD). Evidence from our laboratory demonstrates that Chinook salmon from Lake MI, Wisconsin have greater survival following R. salmoninarum challenge relative to several Pacific Northwest populations, including its progenitor population (Purcell et al., 2008). A collaborative study between scientists at the Western Fisheries Research Center (USGS) and the Northwest Fisheries Science Center (NOAA Fisheries) seeks to characterize the genetic basis for survival following Renibacterium salmoninarum infection in a Lake MI population of Chinook salmon. We have hypothesized that pathogen-driven selection during the Lake MI BKD epidemics enhanced the ability of the Wisconsin population to resist or tolerate R. salmoninarum infections. If true, a possible trade-off to the fitness gains achieved by selection can be a reduction in the overall genetic variation at the trait, thereby limiting future evolutionary potential. In this study, we are comparing the genetic variation controlling R. salmoninarum survival in the contemporary Wisconsin and Washington Chinook salmon populations. We are also determining if higher R. salmoninarum survival of the Wisconsin population is a stable trait when an environmental parameter shifts, a measure of phenotypic plasticity. The ability to respond and adapt to a changing environment is critical for long-term sustainability of any population. This study is funded by the Great Lakes Fishery Trust.

Related Publications:

Maureen K. Purcell, Anthony L. Murray, Anna Elz, Linda K. Park, Susan V. Marcquenski, James R. Winton, Stewart W. Alcorn, Ronald J. Pascho, and Diane G. Elliott. 2008. Decreased Mortality of Lake Michigan Chinook Salmon after Bacterial Kidney Disease Challenge: Evidence for Pathogen-Driven Selection? Journal of Aquatic Animal Health, 20:4, 225-235. doi: 10.1577/H08-028.1 (online abstract of journal article)

For more information, contact Maureen K. Purcell or Diane G. Elliott at the Western Fisheries Research Center.

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Emerging Virus Threat to Fish in Western Washington

Sequence analysis of new isolates of IHNV
Figure 1. Larger View
d
Figure 2.

A new strain of infectious hematopoietic necrosis virus (IHNV) that is highly lethal for steelhead trout has emerged in rivers of the Olympic Peninsula in Washington State. The M-D strain of IHNV is believed to have originated in the upper Columbia River watershed in the late 1970s where it has continued to evolve and to move downriver to affect additional stocks. The spread of M-D IHNV to geographically separate watersheds in the Olympic Peninsula constitutes a risk to genetically distinct stocks of steelhead trout that are co-managed by tribal, state and federal agencies. In order to understand the epidemiology of M-D IHNV and the risks posed to wild stocks of salmonids in affected watersheds, data on ecological, physical and anthropogenic factors will be compared with sequence analysis (Figure 1) of new isolates of IHNV from the region and elsewhere.

For more information contact Gael Kurath, Western Fisheries Research Center, Seattle, WA.

Figure 1. Isolates of IHNV from the western US fall into three major genetic groups or clades that typically correlate with host and geographic range. The "U" clade is found predominantly in sockeye salmon throughout a wide area of North America, while the "L" clade is principally found in Chinook salmon in Northern California or Southern Oregon. The "M" clade was originally discovered in rainbow trout in the Hagerman Valley of Southern Idaho, but has since spread and become established in steelhead trout in the lower Columbia River.

Figure 2. Phylograms created using Bayesian analysis of sequence data showing the genetic relationships of isolates of IHNV. The new M-D isolates from the Olympic Peninsula are on a branch indicated with an orange arrow.

 

Investigating the Nature of a Putative Virus Isolated from the Introduced Species, the Northern Snakehead (Channa argus), Present in the Chesapeake Bay Watershed
Northern snakehead (Channa argus). Photo credit: USGS, courtesy USGS Southeast Ecological Science Center Photo Gallery
Northern snakehead (Channa argus). Photo credit: USGS, courtesy USGS Southeast Ecological Science Center Photo Gallery

The Northern snakehead (Channa argus) is a piscivorous fish native to eastern Asia. It is the most important snakehead cultured in China and has been purposely introduced to a number of Asian countries due to its culinary attributes. For decades this fish has been imported to the United States as a live product to meet food market and aquarium trade demand. It is believed that accidental or illegal, but purposeful introductions of this species into open waters was an artifact of this permitted live market. While it is not know when this fish was introduced into United States waters, the first documented observation of a live snakehead captured from open waters occurred in California in October of 1997. Since that time Northern snakeheads have been observed in Florida, Maryland, Virginia, North Carolina and the New England states (Courtenay et al. 2004). The presence of Northern snakeheads in the mid-Atlantic region has garnered attention given sensationalized media coverage, coupled by evidence that these populations are expanding (Odenkirk and Owens, 2007). Strategies to eradicate this invasive fish have thus far failed, and it is predicted that the Northern snakehead is likely to increase its present range (Odenkirk and Owens, 2005).

The introduction of non-native, invasive species poses the risk of introducing exotic pathogens.  During a 2006 reconnaissance a filterable agent likely of viral nature was isolated from a number of Northern snakehead in Virgina waters of the Chesapeake Bay Watershed. Classical biological methods and molecular approaches are in progress to identify the putative viral isolate. It is unknown if this agent causes disease in Northern snakehead or poses a threat to endemic species. Likewise it is unclear if the isolates ‘hitchhiked’ into the US water or if the snakeheads became infected post introduction. Active research includes the definitive identification of this isolate, and epidemiological studies to determine the geographical range.

Related Publications:

  • Courtenay, W. R. Jr., and J. D. Williams. 2004. Snakeheads (Pisces, Channidae) - A biological synopsis and risk assessment. U.S. Geological Survey Circular 1251.
  • Odenkirk, J., and S. Owens. 2005. Northern snakeheads in the tidal Potomac River system. Transactions of the American Fisheries Society 134:16051609.
  • Odenkirk, J., and S. Owens. 2007. Expansion of a Northern Snakehead Population in the Potomac River System. Transactions of the American Fisheries Society 136:16331639

For more information contact Luke R. Iwanowicz or Christine Densmore, Leetown Science Center, Fish Health Branch.

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Q-PCR Detection of Bacterial Sources of Thiaminase I, a Potential Cause of Thiamine Deficiency and Early Mortality Syndrome in Great Lakes Salmonines

Yellow agar plate
Yellow color shows thiamine degradation on an agar plate of P. thiaminolyticus strain 8120.  Photo credit: Catherine A. Richter, Columbia Environmental Research Center.

Reproductive success of salmonines, including lake trout, in the Great Lakes has been limited by early mortality syndrome (EMS) due to thiamine (vitamin B1) deficiency in eggs.  The Gram-positive bacterium Paenibacillus thiaminolyticus produces an enzyme, thiaminase I, which degrades thiamine.  While thiamine deficiency may have multiple causes, P. thiaminolyticus is one potential cause of thiamine deficiency leading to EMS in Great Lakes salmonines.  Diets of alewife or isolated strains of P. thiaminolyticus mixed in a semipurified diet and fed to lake trout have been shown to produce EMS in fry.  Furthermore, P. thiaminolyticus has been isolated from viscera of alewife collected in Lake Michigan.  In order to aid studies of the sources of P. thiaminolyticus and thiaminase I, we have developed and characterized quantitative PCR assays for the thiaminase I gene and the 16S rRNA gene of P. thiaminolyticus.  These Q-PCR assays are being applied to identify sources of bacterial thiaminase I in Great Lakes food webs and will be of use in defining the relative importance of this cause of thiamine deficiency and in evaluating the effectiveness of management strategies for prevention of EMS in Great Lakes salmonines.

For more information, contact Catherine A. Richter, Columbia Environmental Research Center.

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Viral Hemorrhagic Septicemia Virus in the Great Lakes
Great Lakes. Photo credit: Jeff Schmaltz/NASA
Great Lakes. Photo credit: Jeff Schmaltz/NASA

Viral hemorrhagic septicemia (VHS) is considered to be the most important viral disease of finfish worldwide and is listed as reportable by many nations and international organizations. Prior to 1988, VHS was not known to occur outside of continental Europe where it affected rainbow trout aquaculture. Subsequently, a North American strain of the causative rhabdovirus, VHSV, was found to be endemic among marine fish on the Pacific coast of North America where it was shown to be highly pathogenic for marine species, especially herring. Surveys in other regions of the world have revealed that VHSV is also endemic among marine species in the North Atlantic, the Baltic Sea, the North Sea and Japan. Beginning in 2005, reports from the Great Lakes region indicated that wild fish had experienced disease or, in some cases, very large die-offs from VHS. The USGS Western Fisheries Research Center (WFRC) has conducted research on VHSV for more than 20 years providing technical assistance and information to fisheries managers at state, federal, tribal and private sector entities as well as to the news media. Research at the WFRC has developed novel tools for the detection and identification of VHSV and used molecular epidemiology to show that the strain of VHSV affecting fish in the Great Lakes Basin is a new genotype of the virus, now identified as Genotype IVb. The type IVb isolate found in the Great Lakes region is the only strain of VHSV that has been linked to large natural mortalities among freshwater species. As of spring 2008, VHSV has been isolated from more than 25 species of fish, some of which suffered substantial mortality, in Lake Michigan, Lake Huron, Lake St. Clair, Lake Erie, Lake Ontario and the St. Lawrence River as well as inland lakes in Wisconsin, Michigan and Ohio.

Links to VHSV Fact Sheets:

For further information contact James R. Winton, Western Fisheries Research Center.

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