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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. [ABSTRACT FROM AUTHOR]

Two variants ofLoma salmonaeoccur in net-pen reared chinook salmon,Oncorhynchus tshawytscha. The typical variant (OA) has a host specificity for salmonids of the genusOncorhynchuswhereas the atypical variant (SV) has a host specificity for brook trout,Salvelinus fontinalis, and in this study, the ultrastructure of the two are compared. In fish at 8 weeks post-exposure xenomas of the SV variant have a very high proportion of mature spores compared with other developmental stages, while in xenomas of the OA variant there are fewer spores and many other developmental stages. Spores of the SV variant had up to 20 turns of their polar tube whereas those of the OA variant only had 17. Furthermore, the spores of the SV variant were significantly larger than those of the OA variant. The sporophorous vesicle for both variants appears to form around a sporogonial plasmodia, which results in many spores developing within the vesicle. [ABSTRACT FROM AUTHOR]

Abstract An 80-year-old man with no history of an immune-compromising disorder was diagnosed with progressive multifocal leukoencephalopathy (PML). He presented with dysphagia and left-sided weakness; magnetic resonance imaging demonstrated marked signal abnormality in the subcortical white matter of the left frontal lobe and in the posterior limb of the right internal capsule. Polymerase chain reaction (PCR) analysis of the cerebrospinal fluid (CSF) was negative for John Cunningham (JC) virus. On brain biopsy, foamy macrophages infiltrating the white matter were identified, staining positive for anti-simian virus 40 antibodies. Postoperatively, PCR for JC viral DNA in the CSF was positive, establishing the diagnosis of PML. Extensive investigation for an occult immunocompromising disorder was negative. The patient's neurologic deficits rapidly increased throughout his hospital stay, and he died 3.5 months after his diagnosis.

The alewife ( Alosa pseudoharengus) is an anadromous herring that inhabits waters of northeastern North America. This prey species is a critical forage for piscivorous birds, mammals, and fishes in estuarine and oceanic ecosystems. During a discovery project tailored to identify potentially emerging pathogens of this species, we obtained the full genome of a novel hepadnavirus (ApHBV) from clinically normal alewives collected from the Maurice River, Great Egg Harbor River, and Delaware River in New Jersey, USA during 2015-2018. This previously undescribed hepadnavirus contained a circular DNA genome of 3146 nucleotides. Phylogenetic analysis of the polymerase protein placed this virus in the clade of metahepadnaviruses (family: Hepadnaviridae ; genus: Metahepadnavirus ). There was no evidence of pathology in the internal organs of infected fish and virions were not observed in liver tissues by electron microscopy. We developed a Taqman-based quantitative (qPCR) assay and screened 182 individuals collected between 2015 and 2018 and detected additional qPCR positives (n = 6). An additional complete genome was obtained in 2018 and it has 99.4% genome nucleotide identity to the first virus. Single-nucleotide polymorphisms were observed between the two genomes, including 7/9 and 12/8 synonymous vs nonsynonymous mutations across the polymerase and surface proteins, respectively. While there was no evidence that this virus was associated with disease in this species, alewives are migratory interjurisdictional fishes of management concern. Identification of microbial agents using de novo sequencing and other advanced technologies is a critical aspect of understanding disease ecology for informed population management.

Anadromous river herring have declined in many parts of their range, leading to fisheries management efforts to help repopulate this species by improving connectivity of rivers and restoring populations by fish transfers. With data lacking on parasites in these species, this study sought to better understand myxozoans across various life stages and habitats in river herring populations in New Jersey, USA. We compared fish from riverine habitats during early-life growth and adults returning to spawn, marine-phase fish, and landlocked Alewife populations. Three myxozoan species were identified in young-of-the-year (YOY) anadromous river herring, including Kudoa clupeidae in the skeletal musculature, Myxobolus mauriensis in the rib cartilage, and an uncharacterized coelozoic myxozoan within the lumen of mesonephric tubules. In YOY river herring, Blueback Herring were 2 times more likely to be infected by K. clupeidae than Alewife (p = 0.019) and in the Maurice River, fish were 4 times more likely to be infected with M. mauriensis than fish from Great Egg Harbor River (p = 0.000) and 11 times more likely than the Delaware River (p = 0.001). Spawning adult river herring were infected with a previously undescribed myxozoan parasite infecting the kidney. Sequencing the 18S rDNA indicated this species is closely related to Ortholinea species. Myxobolus mauriensis and the Ortholinea-like species were absent from marine-phase river herring indicating that infections were linked to river environments occurring during early-life growth and spawning, respectively. No myxozoans were present in landlocked Alewife, showing that similar infections occurring in rivers were absent in lake environments in the region., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The sole member of the Piscihepevirus genus (family Hepeviridae ) is cutthroat trout virus (CTV) but recent metatranscriptomic studies have identified numerous fish hepevirus sequences including CTV-2. In the current study, viruses with sequences resembling both CTV and CTV-2 were isolated from salmonids in eastern and western Canada. Phylogenetic analysis of eight full genomes delineated the Canadian CTV isolates into two genotypes (CTV-1 and CTV-2) within the Piscihepevirus genus. Hepevirus genomes typically have three open reading frames but an ORF3 counterpart was not predicted in the Canadian CTV isolates. In vitro replication of a CTV-2 isolate produced cytopathic effects in the CHSE-214 cell line with similar amplification efficiency as CTV. Likewise, the morphology of the CTV-2 isolate resembled CTV, yet viral replication caused dilation of the endoplasmic reticulum lumen which was not previously observed. Controlled laboratory studies exposing sockeye ( Oncorhynchus nerka) , pink ( O. gorbuscha ), and chinook salmon ( O.   tshawytscha ) to CTV-2 resulted in persistent infections without disease and mortality. Infected Atlantic salmon ( Salmo salar ) and chinook salmon served as hosts and potential reservoirs of CTV-2. The data presented herein provides the first in vitro and in vivo characterization of CTV-2 and reveals greater diversity of piscihepeviruses extending the known host range and geographic distribution of CTV viruses.

Wild bluegill, Lepomis macrochirus Rafinesque, succumb to seasonal mortality in the early spring during cool water temperatures, shown previously to be related to bacteraemia caused by a psychrotrophic bacterium, Pseudomonas mandelii. In the study herein, intestinal coccidiosis in wild bluegill had seasonal prevalence causing heavy intestinal infections and sloughing of intestinal epithelium occurring in late winter/early spring. Infections were predominantly related to two different species, Goussia washuti n. sp., an epicellular coccidium, and a coccidium closely resembling Goussia desseri Molnár 1996, previously only described in percid fish in Europe. In 2019, co-infections of bacteraemia and intestinal coccidiosis occurred in bluegills. Evaluating coccidium infection intensity by fresh parasite examination and histology, an association was observed in which fish with moderate-to-heavy intestinal coccidiosis were 8-12 times more likely to have bacteraemia compared to fish with no or light coccidiosis. The association of these co-infections suggests that intestinal coccidiosis could contribute to seasonal bacterial epizootics of wild bluegill., (© 2019 John Wiley & Sons Ltd.)

:  River herring populations, including Alosa pseudoharengus and Alosa aestivalis , have significantly declined as a result of anthropogenic factors throughout their range in eastern North America. To better understand the health of the species, parasite surveys were conducted in several New Jersey rivers. A novel myxozoan parasite, Myxobolus mauriensis n. sp., is described infecting the cartilage of pleural ribs in young-of-the-year fish. The parasite forms large polysporic plasmodia forming pseudocysts within the ribs, which extend into the musculature. Pathology associated with infection includes costochondritis, breaks in the rib bones, and deformed bone growth. Rupture of large pseudocysts and release of mature spores are associated with myositis, dermatitis, and peritonitis. Phylogenetic analysis reveals that M. mauriensis n. sp. occurs in a long-branching clade basal to other myxobolids, grouping with several Myxobolus species from marine fish (Myxobolus groenlandicus, Myxobolus aeglefini, and Myxobolus albi). The closest identity is to M. groenlandicus, with 83% identity based on a 1,762-bp sequence of the SSU 18S rDNA. Similarly, spore morphology, tropism for cartilage, and association with marine/brackish environments are shared in these 4 species. Mature spores of M. mauriensis n. sp. are similar to other reported myxobolids, though spores are slightly wider (12.1 ± 0.44 μm) than long (11.4 ± 0.44 μm), with a length:width relationship of 0.94 (±0.04), a feature not commonly described for other species of Myxobolus. Prevalence was studied by histology and fresh observation. In both Blueback Herring and Alewife, the highest infection prevalence occurred in the Maurice River at around 20%, and lower prevalence was found in the Great Egg Harbor River at around 5%. In the Delaware River, prevalence was about 2% in Blueback Herring, while the parasite was not detected in Alewife samples.

Anadromous alewives, Alosa pseudoharengus, have experienced significant population level declines caused by factors including habitat destruction. Alewives occur in two different life histories, anadromous and landlocked forms. The landlocked alewife evolved from ancestral anadromous populations, resulting in an exclusively freshwater and phenotypically unique form. The occurrence of parasites in a host is linked to the environment, making alewives an ideal model to compare parasitology within a single species with contrasting life histories. Currently, little information exists on the presence and impacts of parasites in these fish populations; the present study sets out to better understand coccidiosis in the threatened anadromous populations and to understand how coccidian parasites compare in both life history forms. The intestinal coccidian, Goussia ameliae n. sp., was described infecting the pyloric cecum of 76% and 86% of young-of-the-year and adult anadromous alewives, respectively, from the Maurice River, New Jersey, USA. The coccidian was found in landlocked alewife populations with a prevalence of 92% and 34% in YOY and adult fish, respectively. An analysis of the small subunit 18S ribosomal RNA gene of G. ameliae from both life history forms demonstrated that the coccidian had 100% sequence identity, confirming the same parasite species in both forms. Though genetic analysis demonstrated G. ameliae to be identical, some differences were observed in sporulation and morphology of the parasite within the two populations. The sporocysts in anadromous populations were shorter and wider, and sporulation timing differed from that of landlocked fish. These differences may either be attributed to differences in the host type or to the sporulation environment. Lastly, alewives from landlocked populations were frequently co-infected with a second coccidian species in the posterior intestine, which occurred at a lower prevalence. This species, G. alosii n. sp., was described based on morphological characters of the sporulated oocysts in fresh parasitological preparations.

Viral haemorrhagic septicaemia virus (VHSV) is a fish pathogen found throughout the Northern Hemisphere and is capable of infecting and causing mortality in numerous marine and freshwater hosts. In the coastal waters of British Columbia, Canada, the virus has been detected for 20 yr with many occurrences of mass mortalities among populations of Pacific herring Clupea pallasii (Valenciennes) and sardine Sardinops sagax as well as detections among cultured Atlantic Salmo salar and Chinook Oncorhynchus tshawytscha salmon. We compared nucleotide sequence of the full glycoprotein (G) gene coding region (1524 nt) of 63 VHSV isolates sampled during its recorded presence from 1993 to 2011 from 6 species and a total of 29 sites. Phylogenetic analysis showed that all isolates fell into sub-lineage IVa within the major VHSV genetic group IV. Of the 63 virus isolates, there were 42 unique sequences, each of which was ephemeral, being repeatedly detected at most only 1 yr after its initial detection. Multiple sequence types were revealed during single viral outbreak events, and genetic heterogeneity was observed within isolates from individual fish. Moreover, phylogenetic analysis revealed a close genetic linkage between VHSV isolates obtained from pelagic finfish species and farmed salmonids, providing evidence for virus transmission from wild to farmed fish.

The ontogeny and disease responses of Langerhans-like cells within lymphoid tissues of Atlantic salmon, Salmo salar, and rainbow trout, Oncorhynchus mykiss, were investigated. These cells were studied in situ with the use of two markers: the ultrastructural presence of Birbeck-like granules and immunohistochemistry with an antibody against human langerin/CD207 that cross-reacts with salmonid tissues. The appearance of Birbeck-like granules was observed in rainbow trout at 2 weeks post-hatch (PH) in the thymus and anterior kidney prior to the development of the spleen. Spleen first appeared at 3 weeks PH in both Atlantic salmon and rainbow trout, and Birbeck-like granules were observed within cells of the newly developed spleens. The cross-reactivity of langerin as seen by immunohistochemistry was not clearly observed in kidney and spleen until 9 weeks PH, when a strong cytoplasmic reaction was observed. To study langerin-positive cells in spleen and kidney during disease, microsporidial gill disease (MGD) in rainbow trout was used as a known disease model inducing a strong cell-mediated adaptive immune response. Langerin-positive cells in healthy fish were seen predominantly in the spleen, and only low numbers were present in the anterior kidney. During MGD, langerin-positive cell numbers were elevated in the anterior kidney and were significantly higher during 5, 6, and 10 weeks post-exposure (PE) compared with healthy control tissue. During MGD, the distribution of langerin-positive cells in the spleen and anterior kidney shifted from having significantly higher numbers of cells in the spleen than in the kidney in controls and at 1 and 4 weeks PE to having a similar distribution of the cells in the two organs at 2, 3, 5, and 6 weeks PE. By 10 weeks PE, significantly higher numbers of langerin-positive cells occurred in the anterior kidney compared with the spleen.

We studied the morphology and occurrence of splenic Langerhans-like (LL) cells in species representing 11 orders of ray-finned fishes, Actinopterygii. LL cells were frequent in spleen tissue of species among Cypriniformes, Esociformes, Salmoniformes, and Pleuronectiformes. These cells contained granules which resembled Birbeck granules known to occur in mammalian Langerhans cells. The ultrastructure of LL cells in Northern pike, Esox lucius, and in Atlantic halibut, Hippoglossus hippoglossus were similar to those reported in salmonids. LL cells found in cyprinids shared some characteristics with the LL cells in other Actinopterygii species, although unique structures distinguished them from the latter. They contained dense bodies within the Birbeck-like (BL) granules, a characteristic that was never observed in species outside the Cypriniformes. Two types of BL granules were characterized in cyprinid LL cells. The ultrastructure of BL granules across the species is discussed. LL cells in all Actinopterygii species demonstrated close contacts with nearby cells, characterized by adherens-like junctions. Additionally, multivesicular bodies were present within the cytoplasm and large aggregates of exosomes were observed closely associated with the plasma membrane suggesting their release from the cells. These structures are discussed in relation to mammalian dendritic cells. Macrophages found in European perch, Perca fluviatilis, blue gourami, Trichogaster trichopterus, and Atlantic halibut, Hippoglossus hippoglossus contained lysosomes and residual bodies with structures resembling Birbeck granules. These granules and cells were clearly distinct from LL cells., (© 2010 Wiley-Liss, Inc.)

An 80-year-old man with no history of an immune-compromising disorder was diagnosed with progressive multifocal leukoencephalopathy (PML). He presented with dysphagia and left-sided weakness; magnetic resonance imaging demonstrated marked signal abnormality in the subcortical white matter of the left frontal lobe and in the posterior limb of the right internal capsule. Polymerase chain reaction (PCR) analysis of the cerebrospinal fluid (CSF) was negative for John Cunningham (JC) virus. On brain biopsy, foamy macrophages infiltrating the white matter were identified, staining positive for anti-simian virus 40 antibodies. Postoperatively, PCR for JC viral DNA in the CSF was positive, establishing the diagnosis of PML. Extensive investigation for an occult immunocompromising disorder was negative. The patient's neurologic deficits rapidly increased throughout his hospital stay, and he died 3.5 months after his diagnosis.

The presence of dendritic cells in fish is studied with immunohistochemistry using a commercially available antibody developed against Langerin/CD207 present in human Langerhans cells. Langerin/CD207, a protein known to be associated with the development of Birbeck granules in human and murine systems, was found to be expressed within the cytoplasm of spleen and head kidney cells of Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). Reactivity was also observed within a few number of cells within the head kidney of Atlantic salmon, but not observed in any other tissues examined. Immunohistochemical results showed Langerin/CD207 reactivity in the cytoplasm of cells in Atlantic salmon and rainbow trout comparable to reactivity seen in human Langerhans cells. The results in this study further corroborate the presence of dendritic cells with remarkable similarities to human Langerhans cells in the spleens and to a lesser extent in head kidney of salmonids.

This report is the first morphological description of cells that resemble dendritic cells, which appear to form resident populations within the spleen and anterior kidney of fish. Based on examination of three salmonid species, including, rainbow trout, brook trout, and Atlantic salmon, the cells were most abundant in the spleen, although they were always present in the anterior kidney. The cells appeared diffusely distributed, often near blood vessels of the spleen and kidney of healthy fish and within the epithelium, connective tissue, and blood vessels of rainbow trout gills with experimentally induced microsoporidial gill disease. The dendritic-like cells in this study contained granules that resemble Birbeck granules, which are considered to be morphological markers of Langerhans cells in mammals. The cells were approximately 6 mum in diameter and contained Birbeck-like (BL) granules localized near centrioles. Although the dendritic-like cells in the three salmonid species shared many similarities, morphological differences were found in the fine structure of the rod portion of the BL granules. Rainbow trout BL granules contained amorphous material, while the other salmonid species contained particulate material arranged in a square-lattice arrangement. The BL granules in the cells of Atlantic salmon had a narrow diameter and contained four layers of particulate material when sectioned longitudinally; two layers enveloped by the granule membrane and two central layers making up a central lamella, which is common in mammalian Birbeck granules., (2008 Wiley-Liss, Inc)

The purpose of this study was to determine adequate dose ranges and to test for side effects associated with chronic treatment of fish with indomethacin. Rainbow trout Oncorhynchus mykiss were orally treated with indomethacin at various nominal concentrations: a negative control (0 mg/kg) and low (5 mg/kg), medium (10 mg/kg), and high doses (15 mg/kg) daily for 30 d. A dose-associated mortality was observed, as cumulative mortality was 3, 13, and 33%, respectively, in the three indomethacin dose groups. No lesions were observed grossly or with histopathology in the control and low-dose treatment groups. Gross lesions were observed in the medium- and high-dose groups, including skin ulcers, abdominal distension, and necrosis of abdominal wall muscle. Histopathology of fish in the medium- and high-dosage groups revealed severe granulomatous peritonitis in which a large number of foreign body type giant cells were present around proteinaceous and plant material. The inflammatory response spread from the peritoneum through the somatic muscle to the epidermis, causing lesions within all layers of the skin. A large number of bacteria were noted within the peritonitis, observed both intracellularly and in large aggregates extracellularly. Perforations occurred within the anterior intestine, and the thick muscularis layer was replaced with inflammatory tissue. The present investigation shows that chronic indomethacin treatment produces gastrointestinal side effects in rainbow trout similar to those seen in mammals.