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USGS2025

Highly pathogenic avian influenza virus H5N1 in double-crested cormorants (Nannopterum auritum) of the Chesapeake Bay, USA

Double-crested Cormorants ( Nannopterum auritum ) have historically exhibited low levels of infection and antibodies to avian influenza virus (AIV). The recent global expansion of clade 2.3.4.4b A/goose/Guangdong/1/1996 highly pathogenic (HP) avian influenza virus H5N1 (HPAI H5N1) has resulted in large-scale mortalities across diverse waterbird taxa including cormorants. We sampled 32 and 29 Double-crested Cormorants breeding in the Chesapeake Bay, US, during the summers of 2023 and 2024, respectively, to assess HPAI H5N1 infection and AIV antibodies. Although no mortality was observed in the area, one bird sampled in 2023 was infected with HPAI H5N1. Additionally, 21/31 individuals in 2023 and 10/25 individuals in 2024 for which sera were collected had AIV antibodies. Based on additional testing using hemagglutination inhibition, virus neutralization, and an enzyme-linked lectin assay, 94 and 100% (2023 and 2024, respectively) of the seropositive birds tested positive for antibodies to both H5 and N1, suggesting previous infection with HPAI H5N1. These results are consistent with survival and limited clinical effects related to HPAI H5N1 infections. Furthermore, these results suggest that population immunity to HPAI H5N1 within the Chesapeake Bay might reduce future infections and potential population impacts should HP H5N1 remain on the landscape, though immunity may be waning across time. Because results are based on a single population, additional testing for both infection and antibodies as well as continued monitoring could enhance understanding of antibody persistence.

Maryland, Virginia↗

USGS2012

Roles of inflammatory caspases during processing of zebrafish interleukin-1β in Francisella noatunensis infection

The interleukin-1 family of cytokines are essential for the control of pathogenic microbes but are also responsible for devastating autoimmune pathologies. Consequently, tight regulation of inflammatory processes is essential for maintaining homeostasis. In mammals, interleukin-1 beta (IL-1β) is primarily regulated at two levels, transcription and processing. The main pathway for processing IL-1β is the inflammasome, a multiprotein complex that forms in the cytosol and which results in the activation of inflammatory caspase (caspase 1) and the subsequent cleavage and secretion of active IL-1β. Although zebrafish encode orthologs of IL-1β and inflammatory caspases, the processing of IL-1β by activated caspase(s) has never been examined. Here, we demonstrate that in response to infection with the fish-specific bacterial pathogen Francisella noatunensis , primary leukocytes from adult zebrafish display caspase-1-like activity that results in IL-1β processing. Addition of caspase 1 or pancaspase inhibitors considerably abrogates IL-1β processing. As in mammals, this processing event is concurrent with the secretion of cleaved IL-1β into the culture medium. Furthermore, two putative zebrafish inflammatory caspase orthologs, caspase A and caspase B, are both able to cleave IL-1β, but with different specificities. These results represent the first demonstration of processing and secretion of zebrafish IL-1β in response to a pathogen, contributing to our understanding of the evolutionary processes governing the regulation of inflammation.

Infection and Immunity↗

USGS1972

Location and description of spiral-shaped microorganisms in the normal rat cecum

Some indigenous microorganisms have been shown to localize in certain anatomical sites of the digestive tract of mammals. We studied the ceca of normal adult rats by light and electron microscopy to determine whether any specific bacterial population localizes in this area. All rats studied showed that the crypt was packed with organisms whose morphological character differs from those of the cecal lumen. Organisms localized in the crypt were often identified topographically close to the microvilli of the epithelial cells. These organisms could be differentiated into three types according to their characteristic ultrastructure. Type 1 was a thin spiral-shaped microbe that resembled a Borrelia. Type 2 possessed helically coiled fibers and flagella-like appendages. Type 3 was spiral-shaped but lacked axial fibers. Types 1 and 2 were both capable of penetrating through the crypt epithelium into the lamina propria where they were found in either phagocytes or extracellular locations. These observations are discussed in relation to other host-microflora localization patterns.

Infection and Immunity↗

USGS1973

Serotypes in Saccharomyces telluris: Their relation to source of isolation

Three serotypes have been characterized with three reference strains of Saccharomyces telluris and designated as A, B, and C. One reference strain of Torpulopsis bovina , the imperfect form of S. telluris , belonged to serotype B. Strains (141) of S. telluris isolated from four columbid species were serotyped. All 98 strains of this yeast isolated from Columba livia (feral pigeon) belonged to serotype B. Three other columbid species, C. leucocephala (white-crowned pigeon), C. fasciata (band-tailed pigeon), and Zenaidura macroura (mourning dove) harbored strains of serotype C only. Serotype A was not isolated from any of the avian species.

Infection and Immunity↗

USGS2019

Influenza A prevalence and subtype diversity in migrating teal sampled along the United States Gulf Coast

Wild birds in the order Anseriformes are important reservoirs for influenza A viruses (IAV); however, IAV prevalence and subtype diversity may vary by season, even at the same location. To better understand the ecology of IAV during waterfowl migration through the Gulf Coast of the United States (Louisiana and Texas), surveillance of blue-winged (Spatula discors) and American green-winged (Anas carolinensis) teal was conducted annually during the spring (live-capture; 2012-2017) and fall (hunter-harvested; 2007-2017) at times inferred to coincide with northward and southward movements, respectively, for these waterfowl species. During spring migration, 266 low pathogenicity (LP) IAV positive samples were recovered from 7,547 paired cloacal/oropharyngeal (COP) samples (prevalence: 3.5%; annual range: 1.3%-8.4%). During fall migration, 650 LP IAV positive samples were recovered from 9,493 COP samples (prevalence: 6.8%; annual range: 0.4%-23.5%). Overall, 34 and 20 different IAV subtypes were recovered during fall and spring sampling, respectively. Consistent with previous results for fall migrating ducks, H3 and H4 HA subtypes were most common; however, H4 subtype viruses predominated every year. This is in contrast to the predominance of LP H7 and H10 HA subtype viruses in both species during spring. The N6 and N8 NA subtypes, which were usually associated with H4, were most common during fall; the N6 subtype was not recovered in the spring. These consistent seasonal trends in IAV subtype detection in both species are currently not understood and highlight the need for further research regarding potential drivers of spatiotemporal patterns of infection such as population immunity.

Avian Diseases↗

USGS1991

Demonstration of the salmonid humoral response to Renibacterium salmoninarum using a monoclonal antibody against salmonid immunoglobulin

The specificity of the antibody response of salmonids to Renibacterium salmoninarum antigens was demonstrated by western blotting techniques that utilized a monoclonal antibody against salmonid immunoglobulin. In this study, the specificity of the response in immunized chinook salmon Oncorhynchus tshawytscha was compared with the response in naturally infected chinook salmon and coho salmon O. kisutch , and immunized rabbits. The antibody response in immunized salmon and rabbits and the naturally infected fish was primarily against the 57–58kilodalton protein complex. In addition to recognizing these proteins in the extracellular fraction and whole-cell preparations, antibody from the immunized salmon and rabbits detected four proteins with lower molecular masses. Western blotting techniques allow identification of the specific antigens recognized and are a useful tool for comparing the immunogenicity of different R. salmoninarum preparations. Immunofluorescent techniques with whole bacteria were less sensitive than western blotting in detecting salmonid anti- R. salmoninarum antibody.

Journal of Aquatic Animal Health↗

USGS2012

Induction of anti-viral genes during acute infection with Viral hemorrhagic septicemia virus (VHSV) genogroup IVa in Pacific herring ( Clupea pallasii )

Infection with the aquatic rhabdovirus Viral hemorrhagic septicemia virus (VHSV) genogroup IVa results in high mortality in Pacific herring ( Clupea pallasii ) and is hypothesized to be a potential limiting factor for herring recovery. To investigate anti-viral immunity in the Pacific herring, four immune response genes were identified: the myxovirus resistance ( Clpa- Mx), a major histocompatibility complex IB (named Clpa- UAA.001), the inducible immunoproteosome subunit 9 ( Clpa- PSMB9) and the neutrophil chemotactic factor ( Clpa- LECT2). Reverse transcriptase quantitative PCR (RT-qPCR) assays were developed based on these gene sequences to investigate the host immune response to acute VHSV infection following both injection and immersion challenge. Virus levels were measured by both plaque assay and RT-qPCR and peaked at day 6 during the 10-day exposure period for both groups of fish. The interferon stimulated genes ( Clpa- Mx, −UAA.001, and −PSMB9) were significantly up-regulated in response to VHSV infection at both 6 and 10 days post-infection in both spleen and fin. Results from this study indicate that Pacific herring mount a robust, early antiviral response in both fin and spleen tissues. The immunological tools developed in this study will be useful for future studies to investigate antiviral immunity in Pacific herring.

Fish and Shellfish Immunology↗

USGS1999

Intestinal coccidiosis

Coccidia are a complex and diverse group of protozoan (single-celled organisms) parasites; the coccidia group contains many species, most of which do not cause clinical disease. In birds, most disease-causing or pathogenic forms of coccidia parasites belong to the genus Eimeria. Coccidia usually invade the intestinal tract, but some invade other organs, such as the liver and kidney (see Chapter 27). Clinical illness caused by infection with these parasites is referred to as coccidiosis, but their presence without disease is called coccidiasis. In most cases, a bird that is infected by coccidia will develop immunity from disease and it will recover unless it is reinfected. The occurrence of disease depends, in part, upon the number of host cells that are destroyed by the juvenile form of the parasite, and this is moderated by many factors. Severely infected birds may die very quickly. Often, tissue damage to the bird’s intestine results in interrupted feeding; disruption of digestive processes or nutrient absorption; dehydration; anemia; and increased susceptibility to other disease agents. In cranes, coccidia that normally inhabit the intestine sometimes become widely distributed throughout the body. The resulting disease, disseminated visceral coccidiosis (DVC) of cranes, is characterized by nodules, or granulomas, on the surface of organs and tissues that contain developmental stages of the parasite. Collectively, coccidia are important parasites of domestic animals, but, because each coccidia species has a preference for parasitizing a particular bird species and because of the self-limiting nature of most infections, coccidiosis in freeranging birds has not been of great concern. However, habitat losses that concentrate bird populations and the increasing numbers of captive-reared birds that are released into the wild enhance the potential for problems with coccidiosis.

Information and Technology Report↗

USGS2000

Effects of malaria (Plasmodium relicturm) on activity budgets of experimentally-infected juvenile Apapane (Himatione sanquinea)

We used behavioral, physiological, and parasitological measures to document effects of acute malarial infections on activity budgets of experimentally infected juvenile Apapane ( Himatione sanguinea ). Five of eight birds died within 20 to 32 days after exposure to a single infective mosquito bite. Infected Apapane devoted less time to locomotory activities involving flight, walking or hopping, and stationary activities such as singing, preening, feeding, and probing. The amount of time spent sitting was positively correlated with parasitemia and increased dramatically after infection and between treatment and control groups. Birds that succumbed to infection experienced a significant loss of body mass and subcutaneous fat, whereas surviving Apapane were better able to maintain body condition and fat levels. When rechallenged with the parasite five months after initial infection, surviving birds experienced no increase in parasitemia, indicating that they had become immune to reinfection. Regardless of the outcome, infected birds experienced acute illness that would have left them unable to forage or to escape from predators in the wild.

Hawai'i↗

USGS2007

Passive immunization of pigeons against trichomoniasis

Nonimmune homing pigeons Columba livia were infected with the Jones' Barn strain of Trichomonas gallinae and subsequently transfused with plasma from acute or chronically infected pigeons harboring one of 3 different strains of T. gallinae. The transfusions were either a single 2 ml dose given one day after inoculation or three 1 ml doses given 0, 5, and 10 days after inoculation. Plasma from pigeons harboring any of the 3 strains was capable of passively immunizing nonimmune birds. All birds which were immunized with plasma from infected pigeons survived until killed at the end of the test period and no visceral lesions were found on necropsy but trichomonads were present in the oropharynx. All controls (untreated or transfused with normal plasma) died of visceral trichomoniasis. Immune plasma produced some lysis of trichomonads in vitro, and inhibition of motility and vacuolization occurred in some of the non-lysed organisms. The overall lytic activity in vitro affected less than 10% of the suspended trichomonads.

Journal of Protozoology↗

USGS2004

Quantitative expression profiling of immune response genes in rainbow trout following infectious haematopoietic necrosis virus (IHNV) infection or DNA vaccination

Infectious haematopoietic necrosis virus (IHNV) is a well-studied virus of salmonid fishes. A highly efficacious DNA vaccine has been developed against this virus and studies have demonstrated that this vaccine induces both an early and transient non-specific anti-viral phase as well as long-term specific protection. The mechanisms of the early anti-viral phase are not known, but previous studies noted changes in Mx gene expression, suggesting a role for type I interferon. This study used quantitative real-time reverse transcriptase PCR methodology to compare expression changes over time of a number of cytokine or cytokine-related genes in the spleen of rainbow trout following injection with poly I:C, live IHNV, the IHNV DNA vaccine or a control plasmid encoding the non-antigenic luciferase gene. The target genes included Mx-1, viral haemorrhagic septicaemia virus induced gene 8 (Vig-8), TNF-α1, TNF-α2, IL-1β1, IL-8, TGF-β1 and Hsp70. Poly I:C stimulation induced several genes but the strongest and significant response was observed in the Mx-1 and Vig-8 genes. The live IHN virus induced a significant response in all genes examined except TGF-β1. The control plasmid construct and the IHNV DNA vaccine marginally induced a number of genes, but the main difference between these two groups was a statistically significant induction of the Mx-1 and Vig-8 genes by the IHNV vaccine only. The gene expression profiles elicited by the live virus and the IHNV DNA vaccine differed in a number of aspects but this study confirms the clear role for a type I interferon-like response in early anti-viral defence.

Fish & Shellfish Immunology↗

USGS2014

Pathology in euthermic bats with white nose syndrome suggests a natural manifestation of immune reconstitution inflammatory syndrome

White nose syndrome, caused by Geomyces destructans, has killed more than 5 million cave hibernating bats in eastern North America. During hibernation, the lack of inflammatory cell recruitment at the site of fungal infection and erosion is consistent with a temperature-induced inhibition of immune cell trafficking. This immune suppression allows G. destructans to colonize and erode the skin of wings, ears and muzzle of bat hosts unchecked. Yet, paradoxically, within weeks of emergence from hibernation an intense neutrophilic inflammatory response to G. destructans is generated, causing severe pathology that can contribute to death. We hypothesize that the sudden reversal of immune suppression in bats upon the return to euthermia leads to a form of immune reconstitution inflammatory syndrome (IRIS), which was first described in HIV-infected humans with low helper T lymphocyte counts and bacterial or fungal opportunistic infections. IRIS is a paradoxical and rapid worsening of symptoms in immune compromised humans upon restoration of immunity in the face of an ongoing infectious process. In humans with HIV, the restoration of adaptive immunity following suppression of HIV replication with anti-retroviral therapy (ART) can trigger severe immune-mediated tissue damage that can result in death. We propose that the sudden restoration of immune responses in bats infected with G. destructans results in an IRIS-like dysregulated immune response that causes the post-emergent pathology.

Virulence↗

USGS2016

Susceptibility and antibody response of Vesper Sparrows ( Pooecetes gramineus ) to West Nile virus: A potential amplification host in sagebrush-grassland habitat

West Nile virus (WNV) spread to the US western plains states in 2003, when a significant mortality event attributed to WNV occurred in Greater Sage-grouse ( Centrocercus urophasianus ). The role of avian species inhabiting sagebrush in the amplification of WNV in arid and semiarid regions of the North America is unknown. We conducted an experimental WNV challenge study in Vesper Sparrows ( Pooecetes gramineus ), a species common to sagebrush and grassland habitats found throughout much of North America. We found Vesper Sparrows to be moderately susceptible to WNV, developing viremia considered sufficient to transmit WNV to feeding mosquitoes, but the majority of birds were capable of surviving infection and developing a humoral immune response to the WNV nonstructural 1 and envelope proteins. Despite clearance of viremia, after 6 mo, WNV was detected molecularly in three birds and cultured from one bird. Surviving Vesper Sparrows were resistant to reinfection 6 mo after the initial challenge. Vesper sparrows could play a role in the amplification of WNV in sagebrush habitat and other areas of their range, but rapid clearance of WNV may limit their importance as competent amplification hosts of WNV.

Nevada↗

USGS2015

Demographic and spatiotemporal patterns of avian influenza infection at the continental scale, and in relation to annual life cycle of a migratory host

Since the spread of highly pathogenic avian influenza (HPAI) H5N1 in the eastern hemisphere, numerous surveillance programs and studies have been undertaken to detect the occurrence, distribution, or spread of avian influenza viruses (AIV) in wild bird populations worldwide. To identify demographic determinants and spatiotemporal patterns of AIV infection in long distance migratory waterfowl in North America, we fitted generalized linear models with binominal distribution to analyze results from 13,574 blue-winged teal ( Anas discors , BWTE) sampled in 2007 to 2010 year round during AIV surveillance programs in Canada and the United States. Our analyses revealed that during late summer staging (July-August) and fall migration (September-October), hatch year (HY) birds were more likely to be infected than after hatch year (AHY) birds, however there was no difference between age categories for the remainder of the year (winter, spring migration, and breeding period), likely due to maturing immune systems and newly acquired immunity of HY birds. Probability of infection increased non-linearly with latitude, and was highest in late summer prior to fall migration when densities of birds and the proportion of susceptible HY birds in the population are highest. Birds in the Central and Mississippi flyways were more likely to be infected compared to those in the Atlantic flyway. Seasonal cycles and spatial variation of AIV infection were largely driven by the dynamics of AIV infection in HY birds, which had more prominent cycles and spatial variation in infection compared to AHY birds. Our results demonstrate demographic as well as seasonal, latitudinal and flyway trends across Canada and the US, while illustrating the importance of migratory host life cycle and age in driving cyclical patterns of prevalence.

PLoS ONE↗

USGS2021

Disruption of the Francisella noatunensis orientalis pdpA gene results in virulence attenuation and protection in zebrafish

Several Francisella spp. including F. noatunensis are regarded as important emerging pathogens of wild and farmed fish. However, very few studies have investigated the virulence factors that allow these bacterial species to be pathogenic in fish. The Francisella Pathogenicity Island (FPI) is a well-described, gene-dense region encoding major virulence factors for the genus Francisella. PdpA is a member of the pathogenicity determining protein genes encoded by the FPI that are implicated in the ability of the mammalian pathogen, F. tularensis , to escape and replicate in infected host cells. Using a sacB suicide approach, we generated pdpA knockouts to address the role of PdpA as a virulence factor for F. noatunensis . Because polarity can be an issue in gene-dense regions, we generated two different marker-based mutants in opposing polarity ( Fno Δ pdpA1 and Δ pdpA2 ). Both mutants were attenuated (p<0.0001) in zebrafish challenges and displayed impaired intracellular replication (p<0.05) and cytotoxicity (p<0.05), all of which could be restored to wild-type (WT) levels by complementation for Fno Δ pdpA 1. Importantly, differences were found for bacterial burden and induction of acute phase and pro-inflammatory genes for Fno Δ pdpA 1 and Δ pdpA 2 compared to WT during acute infection. In addition, neither mutant resulted in significant histopathological changes. Finally, immunization with Fno Δ pdpA1 led to protection (p<0.012) against an acute lethal-dose 40 challenge with WT Fno in the zebrafish model of infection. Taken together, this study further demonstrates physiological similarities within the genus Francisella relative to their phylogenetic relationships and the utility of zebrafish for addressing virulence factors for the genus.

Infection and Immunity↗

USGS1999

Controlled field and laboratory studies on VHS and Ichtyophonus in Pacific herring: Section II in Investigations of disease factors affecting declines of Pacific herring populations in Prince William Sound

From 1995 through 1998 the controlled disease studies covered a wide range of topics including virus survival in seawater, development of natural immunity, effects of oil exposure on immunity, effect of synthetic immunosuppressants, epizootiology of VHSV in net pens, antibody production and the natural history of VHS in Pacific herring. Both VHSV and I. hoferi were was observed in fish that reached two-years-old while in captivity. Prior to 2 years old, fish that shown to be. serious pathogens of juvenile hening. A natural age-related resistance to VHS virus plaque assay and resistance to reinfection with the known minimum lethal dose of virus. survived an initial infection by VHSV developed an acquired immunity detectable by in vitro Three years of consecutive monthly sampling of wild 0-year herring in Puget Sound revealed a VHSV carrier rate below 1%, but that this level of virus shedding was adequate to initiate an epizootic under confined conditions, and probably resulted in infection of free-ranging fish also. Over 50% of the virus was recoverable from seawater after 2 hours, was still detectable after six hours, and survived up to 100 h when ovarian fluid was present in the water. Studies in PWS demonstrated that closed pounds play a role in transmission of VHSV to impounded fish steadily increased with confinement time and viral tissue titers were at very high susceptible fish, resulting in the rapid spread of virus within the pens. Prevalence of VHSV from levels in fish being released after 8 days in captivity. Viable virus was also recovered from the water inside and outside the net pens at levels adequate to initiate an epizootic in susceptible fish. of herring and that vitro culture was the most sensitive method for detecting it. Studies on Ichthyophonus hoferi demonstrated that the organism is a potential serious pathogen No evidence for increased susceptibility, mortality or loss of disease resistance was observed in wild or laboratory-reared herring exposed to oil or synthetic corticosteroids, either prior to or following exposure to VHSV.

Report↗

USGS2005

A cohabitation challenge to compare the efficacies of vaccines for bacterial kidney disease (BKD) in chinook salmon Oncorhynchus tshawytscha

The relative efficacies of 1 commercial and 5 experimental vaccines for bacterial kidney disease (BKD) were compared through a cohabitation waterborne challenge. Groups of juvenile chinook salmon Oncorhynchus tshawytscha were vaccinated with one of the following: (1) killed Renibacterium salmoninarum ATCC 33209 (Rs 33209) cells; (2) killed Rs 33209 cells which had been heated to 37??C for 48 h, a process that destroys the p57 protein; (3) killed R. salmoninarum MT239 (Rs MT239) cells; (4) heated Rs MT239 cells; (5) a recombinant version of the p57 protein (r-p57) emulsified in Freund's incomplete adjuvant (FIA); (6) the commercial BKD vaccine Renogen; (7) phosphate-buffered saline (PBS) emulsified with an equal volume of FIA; or (8) PBS alone. Following injection, each fish was marked with a subcutaneous fluorescent latex tag denoting its treatment group and the vaccinated fish were combined into sham and disease challenge tanks. Two weeks after these fish were vaccinated, separate groups of fish were injected with either PBS or live R. salmoninarum GL64 and were placed inside coated-wire mesh cylinders (liveboxes) in the sham and disease challenge tanks, respectively. Mortalities in both tanks were recorded for 285 d. Any mortalities among the livebox fish were replaced with an appropriate cohort (infected with R. salmoninarum or healthy) fish. None of the bacterins evaluated in this study induced protective immunity against the R. salmoninarum shed from the infected livebox fish. The percentage survival within the test groups in the R. salmoninarum challenge tank ranged from 59% (heated Rs MT239 bacterin) to 81 % (PBS emulsified with FIA). There were no differences in the percentage survival among the PBS-, PBS/FIA-, r-p57-and Renogen-injected groups. There also were no differences in survival among the bacterin groups, regardless of whether the bacterial cells had been heated or left untreated prior to injection. ?? Inter-Research 2005.

Diseases of Aquatic Organisms↗

USGS2001

Epidemiology of viral hemorrhagic septicemia (VHS) among juvenile Pacific herring and Pacific sandlances in Puget Sound, Washington

Viral hemorrhagic septicemia (VHS) and the associated virus (VHSV) were identified in newly metamorphosed Pacific herring Clupea pallasi and Pacific sand lances Ammodytes hexapterus captured from Puget Sound, Washington, between 1995 and 1998. During that 4-year period, virus was detected in less than 1% of free-ranging, age-0 Pacific herring; however, when groups of these fish were confined in the laboratory, they experienced severe mortality, occasionally exceeding 50%, with the prevalence of VHSV reaching 100% by 14 d postcapture. At 7–21 d postcapture, VHSV titers peaked in excess of 108 plaque-forming units/g of tissue; by 30 d postcapture, however, the virus could no longer be isolated. Fish surviving beyond 30 d eliminated the virus from their tissues, but some remained lethargic and continued to show signs of hemorrhage around the mouth, skin, and fins until about 6 weeks postcapture. No cutaneous ulcers were observed during either the acute or the recovery phases of infection. Eighteen-month-old Pacific herring captured from the same area were also negative for VHSV but developed active infections after confinement for 7 d. Unlike younger fish, only 8.4% of these older fish died of VHS, and 7.7% of survivors were positive for VHSV at 7–10 d postcapture, which suggests that a higher proportion of the older fish had developed resistance to VHSV from prior exposure to it. Three months after fatalities ceased in the laboratory-held fish, the surviving fish were challenged with 5 3 103 plaque-forming units/mL of VHSV for 1 h. No mortality was observed during the next 30 d, and virus was recoverable at very low titers in fewer than 5% of the challenged fish, indicating the development of an active immunity to VHSV. Laboratory cohabitation of infected wild Pacific herring with laboratory-reared, specific-pathogen-free Pacific herring resulted in transmission of VHSV to the nonimmune fish, with the resulting course of disease resembling that seen in wild Pacific herring confined in the laboratory. The possible effects of VHS on stocks of Pacific herring are discussed.

Journal of Aquatic Animal Health↗