Viral hemorrhagic septicemia virus (VHSV) is an aquatic rhabdovirus causing severe disease in numerous freshwater and saltwater fish species. Initially the virus was been found to cause disease in European fish populations starting around 1938 and was first detected in North America in the late 1980s. Of the four VHSV genotypes (I, II, III, and IV), the North American subtype IVb isolates have a broad host range. To determine whether endangered pallid sturgeon Scaphirhynchus albus, are susceptible to VHSV-IVb infection, juvenile pallid sturgeon and two pallid sturgeon cell lines derived from skin and spleen tissue were tested. Detection of viable virus via a plaque assay and molecular detection of the virus results by a RT-PCR (reverse transcription-polymerase chain reaction) confirmed VHSV-IVb in vitro replication in pallid sturgeon cell lines. Pallid sturgeon were also susceptible to VHSV-IVb infection when exposed to the virus by immersion at concentration of 5 X 10e5 plaque forming units per milliliter (pfu/ml) and by injection at a dose of 1 X 10e6 plaque forming units per fish (pfu/fish) during 28-day long challenge experiments. However, after widespread mortality occurred in all treatment groups, including control fish, it was determined that the pallid sturgeon stock fish were infected with Missouri River Sturgeon Iridovirus (MRSIV) prior to experimental challenge. Nevertheless, VHSV-exposed fish suffered equal or higher mortalities (38 – 48%) than mock treated (MRSIV-infected) fish (29 – 38%) and histopathology samples showed reduced hematopoietic cells in spleen and kidney tissues and hemorrhage in the gastrointestinal organs only in VHSV-treated fish. These results suggest that pallid sturgeon are susceptible to VHSV-IVb infection, but the degree of pathogenicity was confounded by the underlying MRSIV infection. Our data also suggest that pallid sturgeon may serve as carriers of VHSV because the virus was isolated from surviving fish that showed no clinical signs, yet were positive for both VHSV and MRSIV. Research comparing susceptibility of pathogen-free and MRSIV-infected fish to VHSV-IVb is needed to accurately assess the vulnerability of pallid sturgeon to VHSV-IVb.

Throughout a 20-year biosurveillance period, viral hemorrhagic septicemia virus was isolated in low titers from only 6 / 7,355 opportunistically sampled adult Pacific herring, reflecting the typical endemic phase of the disease when the virus persists covertly. However, more focused surveillance efforts identified the presence of disease hot spots occurring among juvenile life history stages from certain nearshore habitats. These outbreaks sometimes recurred annually in the same temporal and spatial patterns and were characterized by infection prevalence as high as 96%. Longitudinal sampling indicated that some epizootics were relatively transient, represented by positive samples on a single sampling date, and others were more protracted, with positive samples occurring throughout the first 10 weeks of the juvenile life history phase. Sampling and biological data associated with these surveillances are presented in this dataset.

Throughout a 20-year biosurveillance period, viral hemorrhagic septicemia virus was isolated in low titers from only 6 / 7,355 opportunistically sampled adult Pacific herring, reflecting the typical endemic phase of the disease when the virus persists covertly. However, more focused surveillance efforts identified the presence of disease hot spots occurring among juvenile life history stages from certain nearshore habitats. These outbreaks sometimes recurred annually in the same temporal and spatial patterns and were characterized by infection prevalence as high as 96%. Longitudinal sampling indicated that some epizootics were relatively transient, represented by positive samples on a single sampling date, and others were more protracted, with positive samples occurring throughout the first 10 weeks of the juvenile life history phase. Sampling and biological data associated with these surveillances are presented in this dataset.

Spring viremia of carp virus (SVCV) is a rhabdovirus that primarily infects cyprinid finfishes and causes a disease notifiable to the World Organization for Animal Health. Amphibians, which are sympatric with cyprinids in freshwater ecosystems, are considered non-permissive hosts of rhabdoviruses. The potential host range expansion of SVCV in an atypical host species was evaluated by testing the susceptibility of amphibians native to the Pacific Northwest. Larval long-toed salamanders Ambystoma macrodactylum and Pacific tree frog Pseudacris regilla tad-poles were exposed to SVCV strains from genotypes Ia, Ib, Ic or Id by either intraperitoneal injection, immersion, or cohabitation with virus-infected koi Cyprinus rubrofuscus. Cumulative mortality was 100% for salamanders injected with SVCV, 98-100% for tadpoles exposed to virus via immersion, and 0 – 100% for tadpoles cohabited with SVCV-infected koi. Many of the animals that died exhibited clinical signs of disease and SVCV RNA was found by in situ hybridization in tissue sections of immersion-exposed tadpoles, particularly in the cells of the gastrointestinal tract and liver. SVCV was also detected by plaque assay and RT-qPCR testing in both amphibian species regardless of the virus exposure method, and viable virus was detected up to 28 days after initial exposure. Recovery of infectious virus from naïve tadpoles cohabited with SVCV-infected koi further demonstrated that SVCV transmission can occur between classes of ectothermic vertebrates. Collectively, these results indicated that SVCV, a fish rhabdovirus, can be transmitted to and cause lethal disease in two amphibian species. Therefore members of all five of the major vertebrate groups (mammals, birds, reptiles, fish, and amphibians) appear to be vulnerable to rhabdovirus infections.

Spring viremia of carp virus (SVCV) is a rhabdovirus that primarily infects cyprinid finfishes and causes a disease notifiable to the World Organization for Animal Health. Amphibians, which are sympatric with cyprinids in freshwater ecosystems, are considered non-permissive hosts of rhabdoviruses. The potential host range expansion of SVCV in an atypical host species was evaluated by testing the susceptibility of amphibians native to the Pacific Northwest. Larval long-toed salamanders Ambystoma macrodactylum and Pacific tree frog Pseudacris regilla tad-poles were exposed to SVCV strains from genotypes Ia, Ib, Ic or Id by either intraperitoneal injection, immersion, or cohabitation with virus-infected koi Cyprinus rubrofuscus. Cumulative mortality was 100% for salamanders injected with SVCV, 98-100% for tadpoles exposed to virus via immersion, and 0 – 100% for tadpoles cohabited with SVCV-infected koi. Many of the animals that died exhibited clinical signs of disease and SVCV RNA was found by in situ hybridization in tissue sections of immersion-exposed tadpoles, particularly in the cells of the gastrointestinal tract and liver. SVCV was also detected by plaque assay and RT-qPCR testing in both amphibian species regardless of the virus exposure method, and viable virus was detected up to 28 days after initial exposure. Recovery of infectious virus from naïve tadpoles cohabited with SVCV-infected koi further demonstrated that SVCV transmission can occur between classes of ectothermic vertebrates. Collectively, these results indicated that SVCV, a fish rhabdovirus, can be transmitted to and cause lethal disease in two amphibian species. Therefore members of all five of the major vertebrate groups (mammals, birds, reptiles, fish, and amphibians) appear to be vulnerable to rhabdovirus infections.

Infectious hematopoietic necrosis virus (IHNV) is an acute pathogen of salmonids in North America, Europe and Asia that is phylogenetically classified into five major virus genogroups (U, M, L, E and J). The geographic range of the U and M genogroup isolates overlap in the North American Columbia River Basin and Washington Coast region, where these genogroups pose different risks depending on the species of Pacific salmon (Oncorhynchus spp.). For certain management decisions, there is a need to both test for IHNV presence and rapidly determine the genogroup. Herein, we report the development and validation of a U/M multiplex reverse transcription, real-time PCR (RT-rPCR) assay targeting the IHNV nucleocapsid (N) protein gene. The new U/M RT-rPCR is a rapid, sensitive, and repeatable assay capable of specifically discriminating between North American U and M genogroup IHNV isolates. However, one M genogroup isolate obtained from commercially cultured Idaho rainbow trout (O. mykiss) showed reduced sensitivity with the RT-rPCR test, suggesting caution may be warranted before applying RT-rPCR as the sole surveillance test in areas associated with the Idaho trout industry. The new U/M assay had high diagnostic sensitivity (DSe > 94%) and specificity (DSp > 97%) in free-ranging adult Pacific salmon, when assessed relative to cell culture (reference standard) and the previously validated universal N RT-rPCR. The good diagnostic performance of the new U/M assay indicates the new test is suitable for surveillance, diagnosis, and confirmation of IHNV in Pacific salmon from the Pacific Northwest regions where the U and M genogroups overlap.

Infectious hematopoietic necrosis virus (IHNV) is an acute pathogen of salmonids in North America, Europe and Asia that is phylogenetically classified into five major virus genogroups (U, M, L, E and J). The geographic range of the U and M genogroup isolates overlap in the North American Columbia River Basin and Washington Coast region, where these genogroups pose different risks depending on the species of Pacific salmon (Oncorhynchus spp.). For certain management decisions, there is a need to both test for IHNV presence and rapidly determine the genogroup. Herein, we report the development and validation of a U/M multiplex reverse transcription, real-time PCR (RT-rPCR) assay targeting the IHNV nucleocapsid (N) protein gene. The new U/M RT-rPCR is a rapid, sensitive, and repeatable assay capable of specifically discriminating between North American U and M genogroup IHNV isolates. However, one M genogroup isolate obtained from commercially cultured Idaho rainbow trout (O. mykiss) showed reduced sensitivity with the RT-rPCR test, suggesting caution may be warranted before applying RT-rPCR as the sole surveillance test in areas associated with the Idaho trout industry. The new U/M assay had high diagnostic sensitivity (DSe > 94%) and specificity (DSp > 97%) in free-ranging adult Pacific salmon, when assessed relative to cell culture (reference standard) and the previously validated universal N RT-rPCR. The good diagnostic performance of the new U/M assay indicates the new test is suitable for surveillance, diagnosis, and confirmation of IHNV in Pacific salmon from the Pacific Northwest regions where the U and M genogroups overlap.

Rabbit hemorrhagic disease, a notifiable foreign animal disease in the USA, was reported for the first time in wild native North American rabbits and hares in April 2020 in the southwestern USA. Affected species included the Desert Cottontail (Sylvilagus audubonii), Mountain Cottontail (S. nutallii), Black-tailed Jackrabbit (Lepus californicus), and Antelope Jackrabbit (L. alleni). Desert Cottontails (n=7) and Black-tailed Jackrabbits (n=7) collected in April and May 2020 were necropsied at the U.S. Geological Survey National Wildlife Health Center (NWHC) and tested positive for Lagovirus europaeus GI.2, also known as rabbit hemorrhagic disease virus 2 (GI.2/RHDV2/b), by real-time PCR at the U.S. Department of Agriculture’s Foreign Animal Disease Diagnostic Laboratory. Gross and microscopic lesions were similar to those reported in European rabbits (Oryctolagus cuniculus) and other hare (Lepus) species with GI.2/RHDV2/b infection and included epistaxis (12/13; 92%), massive hepatocellular dissociation (14/14; 100%) and necrosis/apoptosis (11/11; 100%), pulmonary congestion (12/12; 100%), edema (12/13; 92%), and hemorrhage (11/12; 92%), and acute renal tubular injury (3/8; 38%). As in previous reports and when compared to historical cases in the NWHC diagnostic database, massive hepatocellular dissociation and necrosis/apoptosis was the most diagnostically distinct finding in GI.2/RHDV2/b-positive rabbits and hares. Based on the apparent susceptibility of North American Sylvilagus and Lepus species to fatal GI.2/RHDV2/b infection, additional work is needed to understand the host range, pathogenicity, and potential population impacts of GI.2/RHDV2/b in North America.

Rabbit hemorrhagic disease, a notifiable foreign animal disease in the USA, was reported for the first time in wild native North American rabbits and hares in April 2020 in the southwestern USA. Affected species included the Desert Cottontail (Sylvilagus audubonii), Mountain Cottontail (S. nutallii), Black-tailed Jackrabbit (Lepus californicus), and Antelope Jackrabbit (L. alleni). Desert Cottontails (n=7) and Black-tailed Jackrabbits (n=7) collected in April and May 2020 were necropsied at the U.S. Geological Survey National Wildlife Health Center (NWHC) and tested positive for Lagovirus europaeus GI.2, also known as rabbit hemorrhagic disease virus 2 (GI.2/RHDV2/b), by real-time PCR at the U.S. Department of Agriculture’s Foreign Animal Disease Diagnostic Laboratory. Gross and microscopic lesions were similar to those reported in European rabbits (Oryctolagus cuniculus) and other hare (Lepus) species with GI.2/RHDV2/b infection and included epistaxis (12/13; 92%), massive hepatocellular dissociation (14/14; 100%) and necrosis/apoptosis (11/11; 100%), pulmonary congestion (12/12; 100%), edema (12/13; 92%), and hemorrhage (11/12; 92%), and acute renal tubular injury (3/8; 38%). As in previous reports and when compared to historical cases in the NWHC diagnostic database, massive hepatocellular dissociation and necrosis/apoptosis was the most diagnostically distinct finding in GI.2/RHDV2/b-positive rabbits and hares. Based on the apparent susceptibility of North American Sylvilagus and Lepus species to fatal GI.2/RHDV2/b infection, additional work is needed to understand the host range, pathogenicity, and potential population impacts of GI.2/RHDV2/b in North America.

Infectious hematopoietic necrosis virus (IHNV) represents one of the most critical challenges for salmonids in the Pacific Northwest. There are three genogroups of IHNV, designated U, M, and L; the U is further delineated into two subgroups, UC and UP, and the M is further delineated into four subgroups (MA – MD). The UP, UC and MD subgroups co-occur in the Columbia River Basin where the host species sockeye salmon, Chinook salmon, and steelhead trout spawn and rear. Field prevalence data shows that UC viruses exhibit a generalist strategy in Chinook, and steelhead, while two other virus lineages, MD and UP, are more consistent with being specialists in steelhead or sockeye salmon, respectively. The L is found in Northern California and is considered a specialist of Chinook salmon. This study sought to understand early entry and replication of the specialist and generalist IHNV strains in three salmonid hosts. Chinook, steelhead and sockeye were exposed by immersion to their specialist viruses (L, MD and UP, respectively) and to the generalist UC virus. As controls, these hosts were also exposed to buffer (mock control) and IHNV variants that were not specialist for their species (non-specialists). Mortality was monitored throughout the experiments. Fish were sampled at early timepoints post-infection (2, 5, and 8 days post-exposure). Kidney and fin tissues were taken to represent external and internal tissues, respectively. Viral load was assessed by reverse transcriptase quantitative PCR (RT-qPCR) targeting the nucleocapsid (N) gene of IHNV. Additional fish from each experimental group were sampled for histopathology but only a subset were processed and analyzed.