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Paul Hershberger

Publications and source records attributed to Paul Hershberger.

At least 37 records · Page 2Linked to original sources
USGS2021

Novel diagnostic tests for the putative agent of bacterial gill disease in Pacific razor clams (Siliqua patula)

Nuclear inclusion X (NIX) is a gamma proteobacteria that infects the nuclei of gill epithelial cells in Pacific razor clams. NIX has been associated with clam die-offs in coastal Washington. A quantitative PCR (qPCR) assay was developed to detect NIX in Pacific razor clams, and assay specificity was confirmed by chromogenic in situ hybridization (CISH). Both tests were applied to evaluate NIX infections in wild Pacific razor clams collected during spring 2019. Consistent with results from earlier histopathological assessments, qPCR and CISH indicated 100% prevalence in razor clams from two Washington beaches and 0% prevalence from two Alaskan beaches.

Alaska, Washington↗
USGS2021

Differential susceptibility of Yukon River and Salish Sea stocks of Chinook salmon Oncorhynchus tshawytscha to ichthyophoniasis

Preliminary evidence suggests that Chinook salmon Oncorhynchus tshawytscha from the Yukon River may be more susceptible to Ichthyophonus sp. infections than Chinook from stocks further south. To investigate this hypothesis in a controlled environment, we experimentally challenged juvenile Chinook from the Yukon River and from the Salish Sea with Ichthyophonus sp. and evaluated mortality, infection prevalence and infection load over time. We found that juvenile Chinook salmon from a Yukon River stock were more susceptible to ichthyophoniasis than were those from a Salish Sea stock. After feeding with tissues from infected Pacific herring Clupea pallasii , Chinook salmon from both stocks became infected. The infection was persistent and progressive in Yukon River stock fish, where infections sometimes progressed to mortality, and histological examinations revealed parasite dissemination and proliferation throughout the host tissues. In Salish Sea-origin fish, however, infections were largely transient; host mortalities were rare, and parasite stages were largely cleared from most tissues after 3-4 wk. Susceptibility differences were evidenced by greater cumulative mortality, infection prevalence, parasite density, proportion of fish demonstrating a cellular response, and intensity of the cellular response among fish from the Yukon River stock. These observed differences between Chinook salmon stocks were consistent when parasite exposures occurred in both freshwater and seawater. These results support the hypothesis that a longer-standing host-pathogen relationship, resulting in decreased disease susceptibility, exists among Salish Sea Chinook salmon than among Yukon River conspecifics.

Diseases of Aquatic Organisms↗
USGS2021

Long-term shedding from fully convalesced individuals indicates that Pacific herring are a reservoir for viral hemorrhagic septicemia virus

Processes that allow viral hemorrhagic septicemia (VHS) virus to persist in the marine environment remain enigmatic, owing largely to the presence of covert and cryptic infections in marine fishes during typical sub-epizootic periods. As such, marine host reservoirs for VHS virus have not been fully demonstrated, nor have the mechanism(s) by which infected hosts contribute to virus perpetuation and transmission. Here, we demonstrate that after surviving VHS, convalesced Pacific herring continue to shed virus at a low rate for extended periods. Further, exposure of previously naïve conspecific sentinels to this shed virus can result in infections for at least 6 mo after cessation of overt disease. This transmission mechanism was not necessarily dependent on the magnitude of the disease outbreak, as prolonged transmission occurred from 2 groups of donor herring that experienced cumulative mortalities of 4 and 29%. The results further suggest that the virus persists in association with the gills of fully recovered individuals, and long-term viral shedding or shedding relapses are related to cooler or decreasing water temperatures. These results provide support for a new VHS virus perpetuation paradigm in the marine environment, whereby the virus can be maintained in convalesced survivors and trafficked from these carriers to sympatric susceptible individuals.

Diseases of Aquatic Organisms↗
USGS2021

Herring Disease Program - Annual Project Report 2012011-E, February 1, 2010-January 31, 2021

We will investigate fish health factors that may be contributing to the failed recovery of Pacific herring populations in Prince William Sound. Field samples will provide infection and disease prevalence data from Prince William Sound and Sitka Sound to inform the age structured assessment (ASA) model, serological data will indicate the prior exposure history and future susceptibility of herring to viral hemorrhagic septicemia virus (VHSV), and diet information will provide insights into the unusually high prevalence of Ichthyophonus that occurs in juvenile herring from Cordova Harbor. Laboratory studies will validate the newly developed plaque neutralization assay as a quantifiable measure of herd immunity against VHS, provide further understanding of disease cofactors including salinity, and investigate possible routes of transmission for Ichthyophonus. Information from the field and laboratory studies will be integrated into the current ASA model and inform a novel ASA-type model that is based on the immune status of herring age cohorts.

Alaska↗
USGS2020

Pacific herring Clupea pallasii are not susceptible to vibriosis from Vibrio anguillarum or V. ordalii under laboratory conditions

The ubiquity of Vibrio spp. throughout the coastal marine waters of the Pacific Northwest of North America raises questions about the susceptibility of native marine fishes, including Pacific herring (Clupea pallasii). Early reports of Vibriolike disease (Rucker et al., 1954; Walford, 1958) and Vibrio sp. isolations (Pacha & Kiehn, 1969) in Pacific herring remain questionable because both occurred while the classification of vibrios was still developing and prior to the availability of techniques capable of discerning viral aetiologies. This study was performed to address these uncertainties by determining the susceptibility of Pacific herring to vibriosis caused by strains of V. anguillarum and V. ordalii.

Journal of Fish Diseases↗
USGS2020

Climate change can drive marine diseases

As an ultimate driver of marine ecosystem processes, climate change is expected to influence proximate disease drivers in marine systems. The observable effects of climate change, including changes in temperature, hypoxia, CO 2 accumulation, precipitation, and storm and cyclone frequencies and intensities, may directly act as proximate drivers of marine disease, especially in poikilotherms. These climate-driven changes are expected to result in the active and passive movement of pathogens and hosts into previously naïve geographical areas, thereby disrupting the long-evolved, stable host–pathogen relationships. Additionally, large-scale ecological changes stemming from climate change are expected to impact pathogen virulence and host susceptibilities. These real and anticipated changes present evolving challenges for resource managers who are charged with managing stochastic marine diseases in a constantly changing environment.

Book chapter↗
USGS2020

Ichthyophonus sp. Infection in Opaleye (Girella nigricans)

Over a 3-year-period, 17 wild-caught opaleye (Girella nigricans) housed in a public display aquarium were found dead without premonitory signs. Grossly, 4 animals had pinpoint brown or black foci on coelomic adipose tissue. Histologically, liver, spleen, heart, and posterior kidney had mesomycetozoan granulomas in all cases; other organs were less commonly infected. Four opaleye had goiter; additional substantial lesions were not identified. Granulomas surrounded melanized debris, leukocytes, and mesomycetozoa represented by folded membranes (collapsed schizont walls), intact schizonts (50- to >200 µm in diameter with a multilaminate membrane), plasmodia (budding from schizonts or free in tissue), or rarely germinal tubes (budding from schizonts). Ichthyophonus was grown from fresh tissues in tissue explant broth cultures of the heart, liver, and/or spleen. Polymerase chain reaction using 18S ribosomal DNA primers amplified a 1730-bp region, and the DNA sequence was most similar to Ichthyophonus hoferi, which is often associated with freshwater aquaculture fish.

Veterinary Pathology↗
USGS2020

Anadromous coastal cutthroat trout Oncorhynchus clarkii clarkii as a host for Argulus pugettensis (Crustacea, Branchiura): Parasite prevalence, intensity and distribution

Coastal cutthroat trout [ Oncorhynchus clarkii clarkii (Richardson, 1836)] from the marine waters of Puget Sound, WA, was documented as a new host for the ectoparasite Argulus pugettensis ( Dana, 1852 ). The prevalence of A. pugettensis was 66% (49 of 74) on cutthroat trout and 0% (0 of 55) on coho salmon [ O. kisutch (Walbaum, 1792)] collected during the winter of 2017/2018. Infestations occurred most frequently on the dorsal surface, with intensities ranging from 1 to 26 argulids per fish (mean intensity 3.94 ± 4.93 S.D.). In contrast, the prevalence of the common salmon louse [ Lepeophtheirus salmonis (Krøyer, 1837)] was 72% for cutthroat trout and 31% for coho salmon. Relative to other native salmonids, little is known regarding the status, ecology and threats for coastal cutthroat trout. New information reported here is a first step in understanding the relationship between this wild, native trout and infestations by parasitic sea lice and should be followed by future studies aimed to identify population level consequences.

Northwest Science↗
USGS2020

Herring Disease Program II 19120111-E - 2019 Annual Report

We will investigate fish health factors that may be contributing to the failed recovery of Pacific herring populations in Prince William Sound. Field samples will provide infection and disease prevalence data from Prince William Sound and Sitka Sound that will inform the ASA model, serological data that will indicate the prior exposure history and future susceptibility of herring to VHS, and diet information that will provide insights into the unusually high prevalence of Ichthyophonus that occurs in juvenile herring from Cordova Harbor. Laboratory studies will validate the newly-developed plaque neutralization assay as a quantifiable measure of herd immunity against VHS, provide further understanding of disease cofactors including temperature and salinity, investigate the possibility of an invertebrate host for Ichthyophonus, and assess the virulence of other endemic pathogens to Pacific herring. Information from the field and laboratory studies will be integrated into the current ASA model, a novel ASA-type model that is based on the immune status of herring age cohorts.

Alaska↗
USGS2019

Intra‐Annual Changes in Waterborne Nanophyetus salmincola

An analysis of daily water samples collected from an index site on Big Soos Creek, Washington indicated intra‐annual differences in the concentrations of waterborne Nanophyetus salmincola. Waterborne concentrations, quantified as gene copies/L, peaked during the fall (October–November 2016), decreased to very low concentrations over the winter (January–March 2017), and then increased in the spring and throughout the summer. High waterborne concentrations of N. salmincola DNA (2 × 106 gene copies/L) corresponded with live N. salmincola cercariae (mean = 3 cercariae/L) that were detected in companion water samples. Spikes in waterborne N. salmincola concentrations in October and November typically coincided with increases in streamflow; this combination resulted in elevated infection pressures during high water events in the fall. The peak in waterborne N. salmincola concentrations corresponded with an accompanying peak in tissue parasite density (metacercariae/posterior kidney) in Coho Salmon Oncorhynchus kisutch that were reared in the untreated water.

Journal of Aquatic Animal Health↗
USGS2019

A geographic hot spot of Ichthyophonus infection in the southern Salish Sea, USA

The prevalence of Ichthyophonus infection in Pacific herring Clupea pallasii was spatially heterogeneous in the southern Salish Sea, Washington State, USA. Over the course of 13 mo, 2232 Pacific herring were sampled from 38 midwater trawls throughout the region. Fork length was positively correlated with Ichthyophonus infection at all sites. After controlling for the positive relationship between host size and Ichthyophonus infection, the probability of infection was approximately 6-fold higher in North Hood Canal than in Puget Sound and the northern Straits (12 vs. 2% predicted probability for a 100 mm fish and 30 vs. 7% predicted probability for a 180 mm fish). Temporal changes in Ichthyophonus infection probability were explained by seasonal differences in fish length, owing to Pacific herring life history and movement patterns. Reasons for the spatial heterogeneity remain uncertain but may be associated with density-dependent factors inherent to the boom-bust cycles that commonly occur in clupeid populations.

Washington↗
USGS2019

Exxon Valdez oil spill long-term herring research and monitoring program final report

This study includes annual field surveys of Ichthyophonus, viral hemorrhagic septicemia virus, and erythrocytic necrosis virus in adult and juvenile Pacific herring (Clupea pallasii) in Prince William Sound, Alaska and several reference populations in Alaska, British Columbia, and Washington. Results from controlled experimental studies with Ichthyophonus indicated that: • Pacific herring could become infected after repeated feedings on simulated infected offal, • Gross external signs of ichthyophoniasis can persist for extended periods without causing direct host mortality, • A novel tool (chromogenic in situ hybridization) was developed to confirm the presence of Ichthyophonus in histological sections, • A circulating stage of Ichthyophonus was detected in the blood of infected hosts, • Ichthyophonus remains viable in a fish carcass for up to 4 weeks and remains infectious for at least 5 days post mortem, • Six distinct genetic types of Ichthyophonus were identified in different hosts throughout the world, • Tissue explant culture was confirmed to be more sensitive than qPCR for detecting low - intensity Ichthyophonus infections directly from fish tissues. Results from controlled experimental studies with viral hemorrhagic septicemia virus indicated that: • Cooler temperatures are more conducive to viral hemorrhagic septicemia epizootics in Pacific herring, • A blocking ELISA was developed to detect fish antibodies to viral hemorrhagic septicemia virus, • A more sensitive plaque neutralization test was optimized to detect herring neutralizing antibodies to viral hemorrhagic septicemia virus, • The relative susceptibility of Pacific herring to other viral hemorrhagic septicemia virus genotypes was assessed, experimental spill-over, amplification, and spill-back was demonstrated between Atlantic salmon (Salmo salar) and Pacific herring, • The efficacy of homologous and heterologous DNA vaccines against viral hemorrhagic septicemia virus was demonstrated in Pacific herring. Controlled experimental studies with erythrocytic necrosis virus resulted in the development of a conventional PCR technique that is capable of the virus in the blood and the development of a quantitative PCR technique that is capable of detecting the virus in any herring tissues.

Report↗
USGS2018

Susceptibility of Nanophyetus salmincola cercariae to formalin, hydrogen peroxide, and seawater

The ability of formalin, PEROX‐AID (hydrogen peroxide), and seawater to kill waterborne Nanophyetus salmincola cercariae was evaluated in vitro. Newly emerged cercariae survived for extended periods in freshwater, with 53–73% survival occurring in negative control groups after 24 h. Exposure to dilutions of formalin reduced this survival time, with 0% of cercariae surviving after 30 min in 450 μL/L, 40 min in 225 μL/L, and 300 min in 113 μL/L. Exposure to PEROX‐AID (hydrogen peroxide) for 1 h resulted in reduced cercarial survival (16.4%) only at the highest concentration (100 μL/L), compared with 100% survival in the untreated controls and all lesser concentrations. Exposure to dilutions of seawater resulted in reduced cercarial survival only at high salinities (15.2–30.3‰), where 10‐min exposures resulted in 0–20% survival. These results provide insights into options for prophylactic water treatment at salmonid enhancement facilities that experience high mortalities due to infections with Nanophyetus salmincola. Further, the intolerance of live cercariae to high salinities indicates that exposure to fish occurs primarily in the freshwater portions of watersheds.

Journal of Aquatic Animal Health↗
USGS2018

Infection by Nanophyetus salmincola and toxic contaminant exposure in out‐migrating steelhead from Puget Sound, Washington: Implications for early marine survival

Out‐migrating steelhead Oncorhynchus mykiss from four Puget Sound rivers and associated marine basins of Puget Sound in Washington State were examined for the parasite, Nanophyetus salmincola in 2014 to determine whether recent trends in reduced marine survival are associated with the presence of this pathogen. A subset of steelhead from three of these river–marine basin combinations was analyzed for the presence of persistent organic pollutants (POPs) to assess whether exposure to these contaminants is a contributing factor to their reduced marine survival. The prevalence and parasite load of N. salmincola were significantly higher in fish from central and southern Puget Sound than in fish from river systems in northern Puget Sound. The proportion of steelhead samples with concentrations of POPs higher than adverse effects thresholds (AETs) or concentrations known to cause adverse effects was also greater in fish from the central and southern regions of Puget Sound than in those from the northern region. Polybrominated diphenyl ether concentrations associated with increased disease susceptibility were observed in 10% and 40% of the steelhead sampled from central and southern Puget Sound regions, respectively, but in none of the fish sampled from the northern region. The AET for polychlorinated biphenyls was exceeded in steelhead collected from marine habitats: 25% of the samples from the marine basins in the central and southern regions of Puget Sound and 17% of samples from northern Puget Sound region. Both N. salmincola and POP levels suggest there are adverse health effects on out‐migrating steelhead from one southern and one central Puget Sound river that have lower early marine survival than those from a river system in northern Puget Sound.

Washington↗
USGS2018

High‐prevalence and low‐intensity Ichthyophonus infections in Pacific Halibut

Ichthyophonus occurred at high prevalence but low intensity in Pacific Halibut Hippoglossus stenolepis throughout the West Coast of North America, ranging from coastal Oregon to the Bering Sea. Infection prevalence in adults was variable on spatial and temporal scales, with the lowest prevalence typically occurring on the edges of the geographic range and highest prevalence consistently occurring inside Prince William Sound, Alaska (58–77%). Additionally, intra‐annual differences occurred at Albatross–Portlock, Alaska (71% versus 32% within 2012), and interannual differences occurred along coastal Oregon (50% in 2012 versus 12% in 2015). The infection prevalence was influenced by host age, increasing from 3% or less among the youngest cohorts (age ≤ 6) to 39–54% among age‐9–17 cohorts, then decreasing to 27% among the oldest (age‐18+) cohorts. There was little indication of significant disease impacts to Pacific Halibut, as the intensity of infection was uniformly low and length at age was similar between infected and uninfected cohorts. These results suggest that Ichthyophonus in Pacific Halibut currently represents a stable parasite–host paradigm in the North Pacific.

Journal of Aquatic Animal Health↗
USGS2018

Ichthyophonus in sport-caught groundfishes from southcentral Alaska

This report of Ichthyophonus in common sport-caught fishes throughout the marine waters of southcentral Alaska represents the first documentation of natural Ichthyophonus infections in lingcod Ophiodon elongates and yelloweye rockfish Sebastes ruberrimus . In addition, the known geographic range of Ichthyophonus in black rockfish S. melanops has been expanded northward to include southcentral Alaska. Among all species surveyed, the infection prevalence was highest (35%, n = 334) in Pacific halibut Hippoglossus stenolepis . There were no gross indications of high-level infections or clinically diseased individuals. These results support the hypothesis that under typical conditions Ichthyophonus can occur at high infection prevalence accompanied with low-level infection among a variety of fishes throughout the eastern North Pacific Ocean, including southcentral Alaska.

Alaska↗
USGS2018

Study 11. Effects of Nanophyetus on the swimming performance and survival of steelhead smolts AND studies to understand and manage the Nanophyetus cercaria

Recent field surveillances indicated that outmigrating steelhead smolts in several south Puget Sound watersheds are infected with the digenean trematode Nanophyetus salmonicola at high prevalence and intensity (Chen et al Accepted). The apparent severity of these infections, especially in the Nisqually and Green / Duwamish Rivers, lead to the hypothesis that Nanophyetus may play a role as a proximate and / or ultimate factor contributing to the early seawater mortality of smolts after entering Puget Sound. This hypothesis was tested during 2016 using controlled laboratory and field based studies that were intended to investigate possible effects of Nanophyetus infection on: 1. the survival of steelhead smolts during their outmigration through Puget Sound, 2. the ability of steelhead smolts to survive transition from freshwater to seawater, 3. the swimming performance of infected steelhead smolts.

Report↗