Geology topics

K.A. Garver

Publications and source records attributed to K.A. Garver.

9 recordsLinked to original sources

USGS2013

Influence of temperature on viral hemorrhagic septicemia (Genogroup IVa) in Pacific herring, Clupea pallasii Valenciennes

An inverse relationship between water temperature and susceptibility of Pacific herring ( Clupea pallasii ) to viral hemorrhagic septicemia, genogroup IVa (VHS) was indicated by controlled exposure studies where cumulative mortalities, viral shedding rates, and viral persistence in survivors were greatest at the coolest exposure temperatures. Among groups of specific pathogen-free (SPF) Pacific herring maintained at 8, 11, and 15 °C, cumulative mortalities after waterborne exposure to viral hemorrhagic septicemia virus (VHSV) were 78%, 40%, and 13%, respectively. The prevalence of survivors with VHSV-positive tissues 25 d post-exposure was 64%, 16%, and 0% (at 8, 11 and 15 °C, respectively) with viral prevalence typically higher in brain tissues than in kidney/spleen tissue pools at each temperature. Similarly, geometric mean viral titers in brain tissues and kidney/spleen tissue pools decreased at higher temperatures, and kidney/spleen titers were generally 10-fold lower than those in brain tissues at each temperature. This inverse relationship between temperature and VHS severity was likely mediated by an enhanced immune response at the warmer temperatures, where a robust type I interferon response was indicated by rapid and significant upregulation of the herring Mx gene. The effect of relatively small temperature differences on the susceptibility of a natural host to VHS provides insights into conditions that preface periodic VHSV epizootics in wild populations throughout the NE Pacific.

Journal of Experimental Marine Biology and Ecology↗

USGS2013

Experimental infection studies demonstrating Atlantic salmon as a host and reservoir of viral hemorrhagic septicemia virus type IVa with insights into pathology and host immunity

In British Columbia, Canada (BC), aquaculture of finfish in ocean netpens has the potential for pathogen transmission between wild and farmed species due to the sharing of an aquatic environment. Viral hemorrhagic septicemia virus (VHSV) is enzootic in BC and causes serious disease in wild Pacific herring, Clupea pallasii, which often enter and remain in Atlantic salmon, Salmo salar, netpens. Isolation of VHSV from farmed Atlantic salmon has been previously documented, but the effects on the health of farmed salmon and the wild fish sharing the environment are unknown. To determine their susceptibility, Atlantic salmon were exposed to a pool of 9 isolates of VHSV obtained from farmed Atlantic salmon in BC by IP-injection or by waterborne exposure and cohabitation with diseased Pacific herring. Disease intensity was quantified by recording mortality, clinical signs, histopathological changes, cellular sites of viral replication, expression of interferon-related genes, and viral tissue titers. Disease ensued in Atlantic salmon after both VHSV exposure methods. Fish demonstrated gross disease signs including darkening of the dorsal skin, bilateral exophthalmia, light cutaneous hemorrhage, and lethargy. The virus replicated within endothelial cells causing endothelial cell necrosis and extensive hemorrhage in anterior kidney. Infected fish demonstrated a type I interferon response as seen by up-regulation of genes for IFNα, Mx, and ISG15. In a separate trial infected salmon transmitted the virus to sympatric Pacific herring. The results demonstrate that farmed Atlantic salmon can develop clinical VHS and virus can persist in the tissues for at least 10 weeks. Avoiding VHS epizootics in Atlantic salmon farms would limit the potential of VHS in farmed Atlantic salmon, the possibility for further host adaptation in this species, and virus spillback to sympatric wild fishes.

Veterinary Microbiology↗

USGS2012

Viral tropism and pathology associated with viral hemorrhagic septicemia in larval and juvenile Pacific herring

Viral hemorrhagic septicemia virus (VHSV) genotype IVa causes mass mortality in wild Pacific herring, a species of economic value, in the Northeast Pacific Ocean. Young of the year herring are particularly susceptible and can be carriers of the virus. To understand its pathogenesis, tissue and cellular tropisms of VHSV in larval and juvenile Pacific herring were investigated with immunohistochemistry, transmission electron microscopy, and viral tissue titer. In larval herring, early viral tropism for epithelial tissues (6d post-exposure) was indicated by foci of epidermal thickening that contained heavy concentrations of virus. This was followed by a cellular tropism for fibroblasts within the fin bases and the dermis, but expanded to cells of the kidney, liver, pancreas, gastrointestinal tract and meninges in the brain. Among wild juvenile herring that underwent a VHS epizootic in the laboratory, the disease was characterized by acute and chronic phases of death. Fish that died during the acute phase had systemic infections in tissues including the submucosa of the gastrointestinal tract, spleen, kidney, liver, and meninges. The disease then transitioned into a chronic phase that was characterized by the appearance of neurological signs including erratic and corkscrew swimming and darkening of the dorsal skin. During the chronic phase viral persistence occurred in nervous tissues including meninges and brain parenchymal cells and in one case in peripheral nerves, while virus was mostly cleared from the other tissues. The results demonstrate the varying VHSV tropisms dependent on the timing of infection and the importance of neural tissues for the persistence and perpetuation of chronic infections in Pacific herring.

Veterinary Microbiology↗

USGS2011

Development of an aquatic pathogen database (AquaPathogen X) and its utilization in tracking emerging fish virus pathogens in North America

The AquaPathogen X database is a template for recording information on individual isolates of aquatic pathogens and is freely available for download (http://wfrc.usgs.gov). This database can accommodate the nucleotide sequence data generated in molecular epidemiological studies along with the myriad of abiotic and biotic traits associated with isolates of various pathogens (e.g. viruses, parasites and bacteria) from multiple aquatic animal host species (e.g. fish, shellfish and shrimp). The cataloguing of isolates from different aquatic pathogens simultaneously is a unique feature to the AquaPathogen X database, which can be used in surveillance of emerging aquatic animal diseases and elucidation of key risk factors associated with pathogen incursions into new water systems. An application of the template database that stores the epidemiological profiles of fish virus isolates, called Fish ViroTrak, was also developed. Exported records for two aquatic rhabdovirus species emerging in North America were used in the implementation of two separate web-accessible databases: the Molecular Epidemiology of Aquatic Pathogens infectious haematopoietic necrosis virus (MEAP-IHNV) database (http://gis.nacse.org/ihnv/) released in 2006 and the MEAP- viral haemorrhagic septicaemia virus (http://gis.nacse.org/vhsv/) database released in 2010.

Journal of Fish Diseases↗

USGS2011

Emergence of viral hemorrhagic septicemia virus in the North American Great Lakes region is associated with low viral genetic diversity

Viral hemorrhagic septicemia virus (VHSV) is a fish rhabdovirus that causes disease in a broad range of marine and freshwater hosts. The known geographic range includes the Northern Atlantic and Pacific Oceans, and recently it has invaded the Great Lakes region of North America. The goal of this work was to characterize genetic diversity of Great Lakes VHSV isolates at the early stage of this viral emergence by comparing a partial glycoprotein (G) gene sequence (669 nt) of 108 isolates collected from 2003 to 2009 from 31 species and at 37 sites. Phylogenetic analysis showed that all isolates fell into sub-lineage IVb within the major VHSV genetic group IV. Among these 108 isolates, genetic diversity was low, with a maximum of 1.05% within the 669 nt region. There were 11 unique sequences, designated vcG001 to vcG011. Two dominant sequence types, vcG001 and vcG002, accounted for 90% (97 of 108) of the isolates. The vcG001 isolates were most widespread. We saw no apparent association of sequence type with host or year of isolation, but we did note a spatial pattern, in which vcG002 isolates were more prevalent in the easternmost sub-regions, including inland New York state and the St. Lawrence Seaway. Different sequence types were found among isolates from single disease outbreaks, and mixtures of types were evident within 2 isolates from individual fish. Overall, the genetic diversity of VHSV in the Great Lakes region was found to be extremely low, consistent with an introduction of a new virus into a geographic region with previously naïve host populations.

Diseases of Aquatic Organisms↗

USGS2009

Infectious haematopoietic necrosis virus genogroup-specific virulence mechanisms in sockeye salmon, Oncorhynchus nerka (Walbaum), from Redfish Lake, Idaho

Characterization of infectious haematopoietic necrosis virus (IHNV) field isolates from North America has established three main genogroups (U, M and L) that differ in host-specific virulence. In sockeye salmon, Oncorhynchus nerka, the U genogroup is highly virulent, whereas the M genogroup is nearly non-pathogenic. In this study, we sought to characterize the virus-host dynamics that contribute to genogroup-specific virulence in a captive stock of sockeye salmon from Redfish Lake in Idaho. Juvenile sockeye salmon were challenged by immersion and injection with either a representative U or M viral strain and sampled periodically until 14 days post-infection (p.i.). Fish challenged with each strain had positive viral titre by day 3, regardless of challenge route, but the fish exposed to the M genogroup virus had significantly lower virus titres than fish exposed to the U genogroup virus. Gene expression analysis by quantitative reverse transcriptase PCR was used to simultaneously assess viral load and host interferon (IFN) response in the anterior kidney. Viral load was significantly higher in the U-challenged fish relative to M-challenged fish. Both viruses induced expression of the IFN-stimulated genes (ISGs), but expression was usually significantly lower in the M-challenged group, particularly at later time points (7 and 14 days p.i.). However, ISG expression was comparable with 3 days post-immersion challenge despite a significant difference in viral load. Our data indicated that the M genogroup virus entered the host, replicated and spread in the sockeye salmon tissues, but to a lesser extent than the U genogroup. Both virus types induced a host IFN response, but the high virulence strain (U) continued to replicate in the presence of this response, whereas the low virulence strain (M) was cleared below detectable levels. We hypothesize that high virulence is associated with early in vivo replication allowing the virus to achieve a threshold level, which the host innate immune system cannot control. ?? 2009 Blackwell Publishing Ltd.

Journal of Fish Diseases↗

USGS2008

In vivo virus growth competition assays demonstrate equal fitness of fish rhabdovirus strains that co-circulate in aquaculture

A novel virus growth competition assay for determining relative fitness of RNA virus variants in vivo has been developed using the fish rhabdovirus, Infectious hematopoietic necrosis virus (IHNV), in juvenile rainbow trout (Oncorhynchus mykiss). We have conducted assays with IHNV isolates designated B, C, and D, representing the three most common genetic subtypes that co-circulate in Idaho trout farm aquaculture. In each assay, groups of 30 fish were immersed in a 1:1 mixture of two genotypes of IHNV, and then held in individual beakers for a 72 h period of in vivo competitive virus replication. Progeny virus populations in each fish were analyzed for the presence and proportion of each viral genotype. In two independent assays of the B:C isolate pair, and two assays of the B:D pair, all fish were co-infected and there was a high level of fish-to-fish variation in the ratio of the two competing genotypes. However, in each assay the average ratio in the 30-fish group was not significantly different from the input ratio of 1:1, indicating equal or nearly equal viral fitness on a host population basis, under the conditions tested. ?? 2008.

Virus Research↗

USGS2005

Efficacy of an infectious hematopoietic necrosis (IHN) virus DNA vaccine in Chinook Oncorhynchus tshawytscha and sockeye O. nerka salmon

The level of protective immunity was determined for Chinook Oncorhynchus tshawytscha and sockeye/kokanee salmon (anadromous and landlocked) O. nerka following intramuscular vaccination with a DNA vaccine against the aquatic rhabdovirus, infectious hematopoietic necrosis virus (IHNV). A DNA vaccine containing the glycoprotein gene of IHNV protected Chinook and sockeye/kokanee salmon against waterborne or injection challenge with IHNV, and relative percent survival (RPS) values of 23 to 86% were obtained under a variety of lethal challenge conditions. Although this is significant protection, it is less than RPS values obtained in previous studies with rainbow trout (O. mykiss). In addition to the variability in the severity of the challenge and inherent host susceptibility differences, it appears that use of a cross-genogroup challenge virus strain may lead to reduced efficacy of the DNA vaccine. Neutralizing antibody titers were detected in both Chinook and sockeye that had been vaccinated with 1.0 and 0.1 ??g doses of the DNA vaccine, and vaccinated fish responded to viral challenges with higher antibody titers than mock-vaccinated control fish. ?? Inter-Research 2005.

Diseases of Aquatic Organisms↗

USGS2003

Two distinct phylogenetic clades of infectious hematopoietic necrosis virus overlap within the Columbia River basin

Infectious hematopoietic necrosis virus (IHNV), an aquatic rhabdovirus, causes a highly lethal disease of salmonid fish in North America. To evaluate the genetic diversity of IHNV from throughout the Columbia River basin, excluding the Hagerman Valley, Idaho, the sequences of a 303 nt region of the glycoprotein gene (mid-G) of 120 virus isolates were determined. Sequence comparisons revealed 30 different sequence types, with a maximum nucleotide diversity of 7.3% (22 mismatches) and an intrapopulational nucleotide diversity of 0.018. This indicates that the genetic diversity of IHNV within the Columbia River basin is 3-fold higher than in Alaska, but 2-fold lower than in the Hagerman Valley, Idaho. Phylogenetic analyses separated the Columbia River basin IHNV isolates into 2 major clades, designated U and M. The 2 clades geographically overlapped within the lower Columbia River basin and in the lower Snake River and tributaries, while the upper Columbia River basin had only U clade and the upper Snake River basin had only M clade virus types. These results suggest that there are co-circulating lineages of IHNV present within specific areas of the Columbia River basin. The epidemiological significance of these findings provided insight into viral traffic patterns exhibited by IHNV in the Columbia River basin, with specific relevance to how the Columbia River basin IHNV types were related to those in the Hagerman Valley. These analyses indicate that there have likely been 2 historical events in which Hagerman Valley IHNV types were introduced and became established in the lower Columbia River basin. However, the data also clearly indicates that the Hagerman Valley is not a continuous source of waterborne virus infecting salmonid stocks downstream.

Diseases of Aquatic Organisms↗