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USGS2008

Inactivation of Ichthyophonus spores using sodium hypochlorite and polyvinyl pyrrolidone iodine

Chlorine and iodine solutions were effective at inactivating Ichthyophonus spores in vitro. Inactivation in sea water increased directly with halogen concentration and exposure duration, with significant differences (P < 0.05) from controls occurring at all chlorine concentrations and exposure durations tested (1.5-13.3 ppm for 1-60 min) and at most iodine concentrations and exposure durations tested (1.2 ppm for 60 min and 5.9-10.7 ppm for 1-60 min). However, 10-fold reductions in spore viability occurred only after exposure to halogen solutions at higher concentrations and/or longer durations (13 ppm total chlorine for 1-60 min, 5.9 ppm total iodine for 60 min, and 10.7 ppm total iodine for 1-60 min). Inactivation efficacy was greater when halogen solutions were prepared in fresh water, presumably because of combined effects of halogen-induced inactivation and general spore instability in fresh water. The results have practical implications for disinfection and biocontainment in research laboratories and other facilities that handle live Ichthyophonus cultures and/or infected fish.

Journal of Fish Diseases↗

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↗

USGS2010

Differential growth of U and M type infectious haematopoietic necrosis virus in a rainbow trout–derived cell line, RTG-2

Infectious haematopoietic necrosis virus (IHNV) is one of the most important viral pathogens of salmonids. In rainbow trout, IHNV isolates in the M genogroup are highly pathogenic, while U genogroup isolates are significantly less pathogenic. We show here that, at a multiplicity of infection (MOI) of 1, a representative U type strain yielded 42‐fold less infectious virus than an M type strain in the rainbow trout–derived RTG‐2 cell line at 24 h post‐infection (p.i.). However, at an MOI of 10, there was only fivefold difference in the yield of infectious virus between the U and M strains. Quantification of extracellular viral genomic RNA suggested that the number of virus particles released from cells infected with the U strain at a MOI of 1 was 47‐fold lower than from M‐infected cells, but U and M virions were equally infectious by particle to infectivity ratios. At an MOI of 1, U strain intracellular viral genome accumulation and transcription were 37‐ and 12‐fold lower, respectively, than those of the M strain at 24 h p.i. Viral nucleocapsid (N) protein accumulation in U strain infections was fivefold lower than in M strain infections. These results suggest that the block in U type strain growth in RTG‐2 cells was because of the effects of reduced genome replication and transcription. The reduced growth of the U strain does not seem to be caused by defective genes, because the U and M strains grew equally well in the permissive epithelioma papulosum cyprini cell line at an MOI of 1. This suggests that host‐specific factors in RTG‐2 cells control the growth of the IHNV U and M strains differently, leading to growth restriction of the U type virus during the RNA synthesis step.

Journal of Fish Diseases↗

USGS2011

Restricted growth of U-type infectious haematopoietic necrosis virus (IHNV) in rainbow trout cells may be linked to casein kinase II activity

Previously, we demonstrated that a representative M genogroup type strain of infectious haematopoietic necrosis virus (IHNV) from rainbow trout grows well in rainbow trout‐derived RTG‐2 cells, but a U genogroup type strain from sockeye salmon has restricted growth, associated with reduced genome replication and mRNA transcription. Here, we analysed further the mechanisms for this growth restriction of U‐type IHNV in RTG‐2 cells, using strategies that assessed differences in viral genes, host immune regulation and phosphorylation. To determine whether the viral glycoprotein (G) or non‐virion (NV) protein was responsible for the growth restriction, four recombinant IHNV viruses were generated in which the G gene of an infectious IHNV clone was replaced by the G gene of U‐ or M‐type IHNV and the NV gene was replaced by NV of U‐ or M‐type IHNV. There was no significant difference in the growth of these recombinants in RTG‐2 cells, indicating that G and NV proteins are not major factors responsible for the differential growth of the U‐ and M‐type strains. Poly I:C pretreatment of RTG‐2 cells suppressed the growth of both U‐ and M‐type IHNV, although the M virus continued to replicate at a reduced level. Both viruses induced type 1 interferon (IFN1) and the IFN1 stimulated gene Mx1, but the expression levels in M‐infected cells were significantly higher than in U‐infected cells and an inhibitor of the IFN1‐inducible protein kinase PKR, 2‐aminopurine (2‐AP), did not affect the growth of U‐ or M‐type IHNV in RTG‐2 cells. These data did not indicate a role for the IFN1 system in the restricted growth of U‐type IHNV in RTG‐2 cells. Prediction of kinase‐specific phosphorylation sites in the viral phosphoprotein (P) using the NetPhosK program revealed differences between U‐ and M‐type P genes at five phosphorylation sites. Pretreatment of RTG‐2 cells with a PKC inhibitor or a p38MAPK inhibitor did not affect the growth of the U‐ and M‐type viruses. However, 100 μ m of the casein kinase II (CKII) inhibitor, 5,6‐dichloro‐1‐β‐ d ‐ribofuranosylbenzimidazole (DRB), reduced the titre of the U type 8.3‐fold at 24 h post‐infection. In contrast, 100 μ m of the CKII inhibitor reduced the titre of the M type only 1.3‐fold at 48 h post‐infection. Our data suggest that the different growth of U‐ and M‐type IHNV in RTG‐2 cells may be linked to a differential requirement for cellular protein kinases such as CKII for their growth.

Journal of Fish Diseases↗

USGS2013

Comparative susceptibility among three stocks of yellow perch, Perca flavescens (Mitchill), to viral haemorrhagic septicaemia virus strain IVb from the Great Lakes

The Great Lakes strain of viral haemorrhagic septicaemia virus IVb (VHSV-IVb) is capable of infecting a wide number of naive species and has been associated with large fish kills in the Midwestern United States since its discovery in 2005. The yellow perch, Perca flavescens (Mitchill), a freshwater species commonly found throughout inland waters of the United States and prized for its high value in sport and commercial fisheries, is a species documented in several fish kills affiliated with VHS. In the present study, differences in survival after infection with VHSV IVb were observed among juvenile fish from three yellow perch broodstocks that were originally derived from distinct wild populations, suggesting innate differences in susceptibility due to genetic variance. While all three stocks were susceptible upon waterborne exposure to VHS virus infection, fish derived from the Midwest (Lake Winnebago, WI) showed significantly lower cumulative % survival compared with two perch stocks derived from the East Coast (Perquimans River, NC and Choptank River, MD) of the United States. However, despite differences in apparent susceptibility, clinical signs did not vary between stocks and included moderate-to-severe haemorrhages at the pelvic and pectoral fin bases and exophthalmia. After the 28-day challenge was complete, VHS virus was analysed in subsets of whole fish that had either survived or succumbed to the infection using both plaque assay and quantitative PCR methodologies. A direct correlation was identified between the two methods, suggesting the potential for both methods to be used to detect virus in a research setting.

Great Lakes↗

USGS2013

Polyphasic characterization of Aeromonas salmonicida isolates recovered from salmonid and non-salmonid fish

Michigan's fisheries rely primarily upon the hatchery propagation of salmonid fish for release in public waters. One limitation on the success of these efforts is the presence of bacterial pathogens, including Aeromonas salmonicida, the causative agent of furunculosis. This study was undertaken to determine the prevalence of A. salmonicida in Michigan fish, as well as to determine whether biochemical or gene sequence variability exists among Michigan isolates. A total of 2202 wild, feral and hatchery-propagated fish from Michigan were examined for the presence of A. salmonicida. The examined fish included Chinook salmon, Oncorhynchus tshawytscha (Walbaum), coho salmon, O. kisutcha (Walbaum), steelhead trout, O. mykiss (Walbaum), Atlantic salmon, Salmo salar L., brook trout, Salvelinus fontinalis (Mitchill), and yellow perch, Perca flavescens (Mitchill). Among these, 234 fish yielded a brown pigment-producing bacterium that was presumptively identified as A. salmonicida. Further phenotypic and phylogenetic analyses identified representative isolates as Aeromonas salmonicida subsp. salmonicida and revealed some genetic and biochemical variability. Logistic regression analyses showed that infection prevalence varied according to fish species/strain, year and gender, whereby Chinook salmon and females had the highest infection prevalence. Moreover, this pathogen was found in six fish species from eight sites, demonstrating its widespread nature within Michigan.

Journal of Fish Diseases↗

USGS2013

Skin pathology in Hawaiian goldring surgeonfish, Ctenochaetus strigosus (Bennett)

Twenty-eight goldring surgeonfish, Ctenochaetus strigosus (Bennett), manifesting skin lesions and originating from the north-western and main Hawaiian Islands were examined. Skin lesions were amorphous and ranged from simple dark or light discolouration to multicoloured tan to white sessile masses with an undulant surface. Skin lesions covered 2–66% of the fish surface, and there was no predilection for lesions affecting a particular part of the fish. Males appeared over-represented. Microscopy revealed the skin lesions to be hyperplasia, melanophoromas or iridophoromas. The presence of skin tumours in a relatively unspoiled area of Hawaii is intriguing. Explaining their distribution, cause and impact on survivorship of fish all merit further study because C. strigosus is an economically important fish in the region.

Hawai'i↗

USGS2015

Detection of Ichthyophonus by chromogenic in situ hybridization

Ichthyophonus hoferi (Plehn & Mulsow 1911 ) is a protistan parasite in the class Mesomycetozoea that infects a large range of marine and freshwater fish (Mendoza, Taylor & Ajello 2002 ; McVicar 2011 ). The broad host and geographic range, which includes both fresh and marine waters of the Northern and Southern Hemispheres, combined with a lack of distinguishing morphological characteristics, have prompted speculation that Ichthyophonus -like organisms in multiple species of fish, as well as reptiles, amphibians, birds and invertebrates, may have been incorrectly classified under a single type species I. hoferi (McVicar 2011 ). At present, only two species, I. hoferi and I. irregularis , are currently recognized within the genus (Rand et al . 2000 ; Mendoza et al . 2002 ). Investigations of ribosomal DNA sequence variation have begun to clarify relationships among Ichthyophonus types (Criscione et al . 2002 ; Rasmussen et al . 2010 ). Here, we will use the term Ichthyophonus to broadly represent all members of the genus regardless of species/subspecies.

Journal of Fish Diseases↗

USGS2015

The parasite Ichthyophonus sp. in Pacific herring from the coastal NE Pacific

The protistan parasite Ichthyophonus occurred in populations of Pacific herring Clupea pallasii Valenciennes throughout coastal areas of the NE Pacific, ranging from Puget Sound, WA north to the Gulf of Alaska, AK. Infection prevalence in local Pacific herring stocks varied seasonally and annually, and a general pattern of increasing prevalence with host size and/or age persisted throughout the NE Pacific. An exception to this zoographic pattern occurred among a group of juvenile, age 1+ year Pacific herring from Cordova Harbor, AK in June 2010, which demonstrated an unusually high infection prevalence of 35%. Reasons for this anomaly were hypothesized to involve anthropogenic influences that resulted in locally elevated infection pressures. Interannual declines in infection prevalence from some populations (e.g. Lower Cook Inlet, AK; from 20–32% in 2007 to 0–3% during 2009–13) or from the largest size cohorts of other populations (e.g. Sitka Sound, AK; from 62.5% in 2007 to 19.6% in 2013) were likely a reflection of selective mortality among the infected cohorts. All available information for Ichthyophonus in the NE Pacific, including broad geographic range, low host specificity and presence in archived Pacific herring tissue samples dating to the 1980s, indicate a long-standing host–pathogen relationship.

Alaska, British Columbia, California, Washington↗

USGS2015

Persistence of external signs in Pacific herring Clupea pallasii Valenciennes with ichthyophoniasis

The progression of external signs of Ichthyophonus infection in Pacific herring Clupea pallasii Valenciennes was highly variable and asynchronous after intraperitoneal injection with pure parasite preparations; however, external signs generally persisted through the end of the study (429 days post-exposure). Observed signs included papules, erosions and ulcers. The prevalence of external signs plateaued 35 days post-exposure and persisted in 73–79% of exposed individuals through the end of the first experiment (147 days post-exposure). Among a second group of infected herring, external signs completely resolved in only 10% of the fish after 429 days. The onset of mortality preceded the appearance of external signs. Histological examination of infected skin and skeletal muscle tissues indicated an apparent affinity of the parasite for host red muscle. Host responses consisted primarily of granulomatous inflammation, fibrosis and necrosis in the skeletal muscle and other tissues. The persistence and asynchrony of external signs and host response indicated that they were neither a precursor to host mortality nor did they provide reliable metrics for hindcasting on the date of exposure. However, the long-term persistence of clinical signs in Pacific herring may be useful in ascertaining the population-level impacts of ichthyophoniasis in regularly observed populations.

Journal of Fish Diseases↗

USGS2016

Tumours in white suckers from Lake Michigan tributaries: Pathology and prevalence

The prevalence and histopathology of neoplastic lesions were assessed in white sucker Catostomus commersonii captured at two Lake Michigan Areas of Concern (AOCs), the Sheboygan River and Milwaukee Estuary. Findings were compared to those observed at two non-AOC sites, the Root and Kewaunee rivers. At each site, approximately 200 adult suckers were collected during their spawning migration. Raised skin lesions were observed at all sites and included discrete white spots, mucoid plaques on the body surface and fins and large papillomatous lesions on lips and body. Microscopically, hyperplasia, papilloma and squamous cell carcinoma were documented. Liver neoplasms were also observed at all sites and included both hepatocellular and biliary tumours. Based on land use, the Kewaunee River was the site least impacted by human activities previously associated with fish tumours and had significantly fewer liver neoplasms when compared to the other sites. The proportion of white suckers with liver tumours followed the same patterns as the proportion of urban land use in the watershed: the Milwaukee Estuary had the highest prevalence, followed by the Root, Sheboygan and Kewaunee rivers. The overall skin neoplasm (papilloma and carcinoma) prevalence did not follow the same pattern, although the percentage of white suckers with squamous cell carcinoma exhibited a similar relationship to land use. Testicular tumours (seminoma) were observed at both AOC sites but not at the non-AOC sites. Both skin and liver tumours were significantly and positively associated with age but not sex.

Journal of Fish Diseases↗

USGS2017

A systematic surveillance programme for infectious salmon anaemia virus supports its absence in the Pacific Northwest of the United States

In response to reported findings of infectious salmon anaemia virus (ISAV) in British Columbia (BC), Canada, in 2011, U.S. national, state and tribal fisheries managers and fish health specialists developed and implemented a collaborative ISAV surveillance plan for the Pacific Northwest region of the United States. Accordingly, over a 3-1/2-year period, 4,962 salmonids were sampled and successfully tested by real-time reverse-transcription PCR. The sample set included multiple tissues from free-ranging Pacific salmonids from coastal regions of Alaska and Washington and farmed Atlantic salmon ( Salmo salar L.) from Washington, all representing fish exposed to marine environments. The survey design targeted physiologically compromised or moribund animals more vulnerable to infection as well as species considered susceptible to ISAV. Samples were handled with a documented chain of custody and testing protocols, and criteria for interpretation of test results were defined in advance. All 4,962 completed tests were negative for ISAV RNA. Results of this surveillance effort provide sound evidence to support the absence of ISAV in represented populations of free-ranging and marine-farmed salmonids on the northwest coast of the United States.

Pacific Northwest↗

USGS2017

Molecular testing of adult Pacific salmon and trout (Oncorhynchus spp.) for several RNA viruses demonstrates widespread distribution of piscine orthoreovirus in Alaska and Washington

This research was initiated in conjunction with a systematic, multiagency surveillance effort in the United States (U.S.) in response to reported findings of infectious salmon anaemia virus (ISAV) RNA in British Columbia, Canada. In the systematic surveillance study reported in a companion paper, tissues from various salmonids taken from Washington and Alaska were surveyed for ISAV RNA using the U.S.-approved diagnostic method, and samples were released for use in this present study only after testing negative. Here, we tested a subset of these samples for ISAV RNA with three additional published molecular assays, as well as for RNA from salmonid alphavirus (SAV), piscine myocarditis virus (PMCV) and piscine orthoreovirus (PRV). All samples ( n = 2,252; 121 stock cohorts) tested negative for RNA from ISAV, PMCV, and SAV. In contrast, there were 25 stock cohorts from Washington and Alaska that had one or more individuals test positive for PRV RNA; prevalence within stocks varied and ranged from 2% to 73%. The overall prevalence of PRV RNA-positive individuals across the study was 3.4% (77 of 2,252 fish tested). Findings of PRV RNA were most common in coho ( Oncorhynchus kisutch Walbaum) and Chinook ( O. tshawytscha Walbaum) salmon.

Alaska, Washington↗

USGS2019

Malignant melanoma of Brown Bullhead (Ameiurus nebulosus) in Lake Memphremagog, Vermont/Quebec

In 2012, brown bullhead ( Ameiurus nebulosus ) with large, raised, black growths were first reported from multiple areas within the Vermont portion of Lake Memphremagog. Subsequent surveys conducted from 2014 to 2017 at two sites within the lake indicated a prevalence of 30% in adult brown bullhead 200 mm and above total length. These lesions ranged from slightly raised smooth black areas to large nodular areas on the body surface and fins and within the oral cavity. Microscopically, these lesions were determined to be malignant melanoma with invasion into surrounding hypodermis, skeletal muscle and bone as well as metastases to gill, ovary and intestine. Liver neoplasms were also observed in 8% of the bullhead collected from Lake Memphremagog in 2015. Neither skin nor liver neoplasms were noted in Ticklenaked Pond, a site used for comparison.

Quebec, Vermont↗

USGS2021

Laboratory infection rates and associated mortality of juvenile Chinook Salmon (Oncorhynchus tshawytscha) from parasitic copepod (Salmincola californiensis)

Pacific salmon ( Oncorhynchus spp.) rearing in lakes and reservoirs above dams have been known to become heavily infected with an ectoparasitic copepod ( Salmincola californiensis ). Little is known about the factors that affect the parasite infection prevalence and intensity. However, previous research suggests that the parasite may negatively affect the fitness and survival of the host fish. The effect of water temperature, confinement and the density of the free-swimming infectious stage of S. californiensis , the copepodid, on infection prevalence and intensity was evaluated by experimentally exposing juvenile Chinook Salmon ( O. tshawytscha ). Infection rates observed in wild populations were achieved under warm water (15–16°C) and high copepodid density (150–300/L) treatment conditions. Infection prevalence and intensity were also significantly higher in larger fish. During the infection experiment, 4.5% of infected fish died within 54 days with mortality significantly related to copepod infection intensity. The potential for autoinfection was compared to cross-infection by cohabitation of infected fish with naïve fish. Previously infected fish had significantly greater infection intensity compared with naïve fish, indicating that infected fish can be reinfected and that they may be more susceptible than naïve fish.

Michigan, Ohio↗

USGS2021

Identification of Aphanomyces invadans, the cause of epizootic ulcerative syndrome, in smallmouth bass (Micropterus dolomieu) from the Cheat River, West Virginia, USA

The oomycete Aphanomyces invadans (Saprolegniales, Oomycetes), the cause of epizootic ulcerative syndrome (EUS), is an OIE (World Organization for Animal Health) reportable pathogen, capable of infecting many fish species worldwide in both freshwater and estuarine environments (Iberahim et al. 2018). Since the discovery of EUS in Japan in 1971 (Egusa and Masuda 1971), it has spread globally and caused substantial fish mortalities and economic losses (Lilley et al. 1998). Cases in the United States have included lesions initially named ulcerative mycosis of Atlantic menhaden Brevoortia tyrannus (Noga et al. 1988) along the Atlantic coast and later confirmed as A. invadans in menhaden from the Chesapeake Bay (Blazer et al. 1999). It has also been reported in several freshwater and estuarine fishes from Florida, including largemouth bass Micropterus salmoides (Sosa et al. 2007) and channel catfish, black bullhead, and bluegill from recreational ponds in Louisiana (Hawke et al. 2003).This communication reports the finding of A. invadans in smallmouth bass Micropterus dolomieu from the Cheat River, West Virginia. During fish health assessments in October 2020, smallmouth bass with grossly observable skin lesions were determined to be infected with A. invadans . We believe this is the first report of A. invadans infection in smallmouth bass and it was not observed during previous health assessments in this region.

West Virginia↗

USGS2022

Progression of infection and detection of Pseudoloma neurophilia in zebrafish Danio rerio Hamilton by PCR and histology

Pseudoloma neurophilia is a critical threat to the zebrafish ( Danio rerio ) model, as it is the most common infectious agent found in research facilities. In this study, our objectives were two-fold: (1) compare the application of diagnostic tools for P. neurophilia and (2) track the progression of infection using PCR and histology. The first experiment showed that whole-body analysis by qPCR (WB-qPCR) can be a standardized process, providing a streamlined diagnostic protocol, without the need for extraction of specific tissues. Evaluating the course of infection in experimentally infected fish, we showed key dynamics in infection. Starting with a low dose exposure of 8000 spores/fish, the prevalence remained low until 92 days post-exposure (dpe), followed by a 30%–40% prevalence by histology or 40%–90% by PCR until the end of the experiment at 334 dpe. WB-qPCR positively detected infection in more fish than histology throughout the study, as WB-qPCR detected the parasite as early as 4 dpe, whereas it was undetected by histology until 92 dpe. We also added a second slide for histologic analyses, showing an increase in detection rate from 24% to 26% when we combined all data from our experiments, but this increase was not statistically significant.

Journal of Fish Diseases↗

USGS2023

Intestinal lesions and parasites associated with senescence and prespawn mortality in Chinook Salmon (Oncorhynchus tshawytscha)

Prespawn mortality (PSM) presents a major problem for the recovery of spring Chinook Salmon ( Oncorhynchus tshawytscha ) populations. In the Willamette River, Oregon, PSM exceeds 90% in some years but factors explaining it are not well understood. We examined intestinal tissue samples using histological slides from over 783 spring Chinook Salmon collected between 2009 and 2021, which included tissues from PSM fish, artificially spawned captive broodstock (BS) and normal river run fish, comprised of trapped (Live) and naturally post-spawned river (RPS) fish collected from the river. We observed degeneration of the intestinal epithelium and loss of villous structure, with concurrent severe enteritis. A natural progression of decline in epithelial integrity (EI) through the summer and fall until spawning and subsequent death was also observed. Live fish exhibited high EI scores (mean = 68%), BS exhibited variable EI scores (35%) and RPS exhibited severe loss of EI (14%). PSM fish exhibited prominent loss of intestinal epithelium with EI scores (13%), very similar to RPS fish, despite having been collected earlier in the year. Hence, we argue that low EI scores are strongly linked with PSM. Ceratonova shasta and Enterocytozoon schreckii were common in all groups, but neither were linked to either PSM or a decline in EI.

Journal of Fish Diseases↗