Infectious Hematopoietic Necrosis Research Articles

Temporal Change in Genetical Lineages of Infectious Hematopoietic Necrosis Virus (IHNV) in the North Kanto Region of Japan from 1981 to 2015

Temporal Change in Genetical Lineages of Infectious Hematopoietic Necrosis Virus (IHNV) in the North Kanto Region of Japan from 1981 to 2015

Synthesis and application of a potential therapeutic coumarin derivative against IHNV in aquaculture

Infectious haematopoietic necrosis virus (IHNV) is one of the most serious pathogens in aquaculture, causing devastating damage to salmonid. In this study, a novel coumarin derivative (DC) was designed and synthesized to evaluate its anti-IHNV effects in vitro and in vivo. DC at the concentration of up to 10 mg/L significantly inhibited IHNV replication in epithelioma papulosum cyprini (EPC) cells with a maximum inhibitory rate of >95%. Additionally, the results revealed that DC treatment significantly suppressed the IHNV-induced cytopathic effect (CPE) in host cells. Moreover, further data found that DC significantly increased superoxide dismutase (SOD), glutathione (GSH) and total antioxidant capacity (T-AOC) activities, and decreased malondialdehyde (MDA) content in EPC cells and in rainbow trout, suggesting that IHNV-induced antioxidant-oxidant imbalance was inhibited by DC. For in vivo studies, DC exhibited an anti-IHNV effect by substantially enhancing the survival rate of virus-infected fish via intraperitoneal injection. Additionally, DC enhanced the levels of IFN-related genes demonstrated that DC indirectly activated IFNs for the clearance of IHNV in rainbow trout. Importantly, the data showed that horizontal transmission of IHNV was reduced by DC in a static cohabitation challenge model, especially for recipient fish in bath treatment, which suggested that DC might be suitable as a possible therapeutic agent for IHNV in aquaculture.

Near-Complete Genome Sequences of 12 Peruvian Strains of Infectious Hypodermal and Hematopoietic Necrosis Virus Infecting the Shrimp Penaeus vannamei.

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is a shrimp virus listed by the World Organisation for Animal Health (OIE). In this study, we report the genomic sequences of 12 IHHNV strains obtained from shrimp samples from aquaculture cultures from the Tumbes region of Peru.

Virus shedding kinetics and unconventional virulence tradeoffs.

Tradeoff theory, which postulates that virulence provides both transmission costs and benefits for pathogens, has become widely adopted by the scientific community. Although theoretical literature exploring virulence-tradeoffs is vast, empirical studies validating various assumptions still remain sparse. In particular, truncation of transmission duration as a cost of virulence has been difficult to quantify with robust controlled in vivo studies. We sought to fill this knowledge gap by investigating how transmission rate and duration were associated with virulence for infectious hematopoietic necrosis virus (IHNV) in rainbow trout (Oncorhynchus mykiss). Using host mortality to quantify virulence and viral shedding to quantify transmission, we found that IHNV did not conform to classical tradeoff theory. More virulent genotypes of the virus were found to have longer transmission durations due to lower recovery rates of infected hosts, but the relationship was not saturating as assumed by tradeoff theory. Furthermore, the impact of host mortality on limiting transmission duration was minimal and greatly outweighed by recovery. Transmission rate differences between high and low virulence genotypes were also small and inconsistent. Ultimately, more virulent genotypes were found to have the overall fitness advantage, and there was no apparent constraint on the evolution of increased virulence for IHNV. However, using a mathematical model parameterized with experimental data, it was found that host culling resurrected the virulence tradeoff and provided low virulence genotypes with the advantage. Human-induced or natural culling, as well as host population fragmentation, may be some of the mechanisms by which virulence diversity is maintained in nature. This work highlights the importance of considering non-classical virulence tradeoffs.

Immunological and metabolic effects of acute sublethal exposure to glyphosate or glyphosate-based herbicides on juvenile rainbow trout, Oncorhynchus mykiss

Glyphosate is a commonly used agrochemical active substance co-formulated in glyphosate-based herbicides (GBHs) whose environmental safety is still a subject of debate in the European Union. We evaluated the effects of acute sublethal exposure to glyphosate on rainbow trout by measuring changes in their metabolic and hemato-immunologic functions and their ability to survive a viral challenge. Juvenile fish were exposed for 96 h to 500 μg L−1 of glyphosate through the active substance alone or two GHBs, Roundup Innovert® and Viaglif Jardin®, and fish were then infected with the infectious hematopoietic necrosis virus. Red and white blood cell counts (RBCC and WBCC), as well as several enzymatic activities (citrate synthase, CS; cytochrome-c oxidase, CCO; lactate dehydrogenase, LDH; glucose-6-phosphate dehydrogenase, G6PDH; acetylcholinesterase, AChE), were measured 96 h after chemical contamination (S1), and 96 h post-viral infection (S2). Mortality rates were monitored, and virus titers at the mortality peaks and seropositivity of the survivors were analyzed at 60 days post-viral infection (S3). Cumulative mortalities, viral titers, and seropositivity induced by virus infection were similar among conditions. Hematological analysis revealed significant increases of 30% for RBCC for Roundup at S1, and of 22% for WBCC at S2. No changes were observed in metabolic enzyme activities at S1. At S2, CCO and G6PDH activities were significantly higher than controls in all the chemically contaminated groups (+61 to 62% and +65 to 138%, respectively). LDH and AChE activities were increased for the Viaglif (p = 0.07; +55%) and for glyphosate and Roundup conditions (p < 0.05, +62 to 79%), respectively. Rainbow trout acutely exposed to glyphosate or GBHs presented no major physiological changes. Viral infection revealed disruptions, potentially modulated by co-formulants, of hematological and metabolic parameters, showing that it is essential to consider the stressful natural environment of fish in the chemical assessment.

Virulence and Infectivity of UC, MD, and L Strains of Infectious Hematopoietic Necrosis Virus (IHNV) in Four Populations of Columbia River Basin Chinook Salmon

Infectious Hematopoietic Necrosis Virus (IHNV) infects juvenile salmonid fish in conservation hatcheries and aquaculture facilities, and in some cases, causes lethal disease. This study assesses intra-specific variation in the IHNV susceptibility of Chinook salmon (Oncorhynchus tshawytscha) in the Columbia River Basin (CRB), in the northwestern United States. The virulence and infectivity of IHNV strains from three divergent virus genogroups are measured in four Chinook salmon populations, including spring-run and fall-run fish from the lower or upper regions of the CRB. Following controlled laboratory exposures, our results show that the positive control L strain had significantly higher virulence, and the UC and MD strains that predominate in the CRB had equivalently low virulence, consistent with field observations. By several experimental measures, there was little variation in host susceptibility to infection or disease. However, a small number of exceptions suggested that the lower CRB spring-run Chinook salmon population may be less susceptible than other populations tested. The UC and MD viruses did not differ in infectivity, indicating that the observed asymmetric field prevalence in which IHNV detected in CRB Chinook salmon is 83% UC and 17% MD is not due to the UC virus being more infectious. Overall, we report little intra-species variation in CRB Chinook salmon susceptibility to UC or MD IHNV infection or disease, and suggest that other factors may instead influence the ecology of IHNV in the CRB.

Pepscan mapping of autophagy-inducing peptides of the glycoprotein of infectious hematopoietic necrosis virus and the effect on viral replication in vitro

Infectious hematopoietic necrosis virus (IHNV) is the main pathogen threatening the aquaculture used by the salmonid industry worldwide. Our previous study showed that IHNV infection induced autophagy activation in epithelioma papulosum cyprinid (EPC) cells, but the relationship between IHNV infectivity and autophagy induction had not yet been addressed. To investigate this question, IHNV was inactivated by ultraviolet (UV) irradiation and the complete protein sequence of IHNV glycoprotein was segmented by pepscan into 43 peptides. The induction of autophagy was analyzed by transmission electron microscopy, confocal fluorescence microscopy, flow cytometry, and western blotting. The results show that UV-inactivated IHNV and viral glycoprotein can induce autophagosome formation, obvious punctate clusters of LC3-II and an elevated LC3-II to LC3-I ratio. All these results suggested that UV-inactivated IHNV and viral glycoprotein can induce autophagy independently of viral infectivity. The flow cytometry and western blotting results show that EPC cells treated with peptide p108 displayed an obvious induction of autophagy (LC3-II increased by approximately 2.5-fold). The cells pretreated with peptide p108 showed a significant inhibition of intracellular viral mRNA replication levels and extracellular viral yields of IHNV. These results suggest that peptide p108 could be a promising drug for use in IHNV prevention, and they lay a new foundation for anti-IHNV drug development.

Virological screening of wild and farmed fish species: Application of innovative Taqman multiplex real-time PCR protocols

Global demand for seafood is growing and fish stock maintenance becomes a pressing issue, making aquaculture production of capital importance in terms of fish resources sustainability. Therefore, fish disease outbreaks are a significant constraint to fisheries trade and aquaculture production, affecting economic development worldwide. In this study, a virological screening in wild and farmed fish populations was performed by two TaqMan multiplex real-time PCR assays developed to identify/quantify, in a single run, four viruses responsible for major economic losses in fisheries, namely: infectious pancreatic necrosis virus (IPNV), infectious hematopoietic necrosis virus (IHNV), viral haemorrhagic septicaemia virus (VHSV) and viral nervous necrosis virus (VNNV). A total of 323 fish were assessed, being the majority from four species from the Atlantic coast: gilthead seabream and seabass, two extensively farmed species in aquaculture and captured in the wild, and sardine and Atlantic horse mackerel, two of the most consumed fish species in Portugal. The genomes of IPNV (genogroup II) and VHSV (genogroup Ie) were detected in one pool of gilthead seabream and one pool of Atlantic horse mackerel, confirming the importance of molecular tools for viral screening, especially in asymptomatic hosts, since viral infections may impart major economic losses to the fish industry.

Infected juvenile salmon can experience increased predation during freshwater migration.

Predation risk for animal migrants can be impacted by physical condition. Although size- or condition-based selection is often observed, observing infection-based predation is rare due to the difficulties in assessing infectious agents in predated samples. We examined predation of outmigrating sockeye salmon (Oncorhynchus nerka) smolts by bull trout (Salvelinus confluentus) in south-central British Columbia, Canada. We used a high-throughput quantitative polymerase chain reaction (qPCR) platform to screen for the presence of 17 infectious agents found in salmon and assess 14 host genes associated with viral responses. In one (2014) of the two years assessed (2014 and 2015), the presence of infectious haematopoietic necrosis virus (IHNv) resulted in 15–26 times greater chance of predation; in 2015 IHNv was absent among all samples, predated or not. Thus, we provide further evidence that infection can impact predation risk in migrants. Some smolts with high IHNv loads also exhibited gene expression profiles consistent with a virus-induced disease state. Nine other infectious agents were observed between the two years, none of which were associated with increased selection by bull trout. In 2014, richness of infectious agents was also associated with greater predation risk. This is a rare demonstration of predator consumption resulting in selection for prey that carry infectious agents. The mechanism by which this selection occurs is not yet determined. By culling infectious agents from migrant populations, fish predators could provide an ecological benefit to prey.

The rise of the syndrome – sub‐optimal growth disorders in farmed shrimp

AbstractThe phenomenon of slow growth in farmed shrimp was observed for the first time in 1989 in Penaeus vannamei as a clinical manifestation of runt deformity syndrome caused by infectious hypodermal and hematopoietic necrosis virus. Subsequently, it was recorded in Penaeus monodon during 2001–2002. Since then, the condition described as monodon slow growth syndrome (MSGS) has been reported from many countries. Though not leading to mortality, retarded growth at the pond level results in significant economic losses. Several potential pathogens have been identified from affected shrimp; however, no confirmed causal relationship has yet been established. Initially, P. vannamei farmed alongside slow growth‐affected P. monodon were unaffected by the condition. Further, experimental studies suggested that P. vannamei was not susceptible. However, in recent years, increasing incidence of severe growth retardation has been reported in farmed P. vannamei. Currently, slow growth is considered as one of the most impactful production‐limiting conditions affecting shrimp farming across Asia. Similar to MSGS, many infectious agents have been detected in slow growth‐affected P. vannamei, especially the microsporidian Enterocytozoon hepatopenaei. Further, genetic and environmental factors have been suggested to play a role. However, the exact cause of slow growth remains elusive, proposing that it may be a multi‐factor syndrome. This review tracks the trajectory of the condition over the period of significant expansion of shrimp farming and postulates that conventional single pathogen/single disease paradigms are insufficient to deal with chronic yield‐limiting syndromes. We suggest more realistic, multi‐dimensional aetiological consideration of syndromic and emerging diseases in shrimp aquaculture.

Research progress on hosts and carriers, prevalence, virulence of infectious hypodermal and hematopoietic necrosis virus (IHHNV)

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is one of the major viral pathogens of penaeid shrimp and it has spread worldwide. IHHNV causes substantial economic loss to the shrimp farming industry and has been listed as a notifiable crustacean disease pathogen by the World Organization for Animal Health (OIE). In this paper, we reviewed studies on the hosts and carriers, prevalence, genotypes and virulence of IHHNV. The pathogenesis mechanisms of IHHNV and the viral interference between IHHNV and white spot syndrome virus (WSSV) were also discussed. The mechanism of IHHNV infection and its virulence difference in different hosts and different developmental stages have not been fully studied yet. The mechanisms underlying viral interference between IHHNV and WSSV are not yet fully understood. Further studies are needed to elucidate the precise molecular mechanisms underlying IHHNV infection and to apply the insights gained from such studies for the effective control and prevention of IHHNV disease.

Studies on infectious myonecrosis virus (IMNV) and infectious hypodermal and hematopoietic necrosis virus (IHHNV) in cultured penaeid shrimp in Egypt.

The present study aimed to diagnose infectious myonecrosis virus (IMNV) and infectious hypodermal and hematopoietic necrosis virus (IHHNV) among cultured penaeid shrimp (Penaeus semisulcatus, n = 120) collected from private farms in 2 Egyptian provinces (Damietta and North Sinai) along the Mediterranean coast. The collected shrimp were subjected to clinical examination, histopathology, molecular characterization, and phylogenetic analysis. Most of the shrimp infected with IMNV showed a distinctive appearance resembling cooked shrimp and white necrosis on distal abdominal segments and tail fans. Simultaneously, IHHNV-infected cases displayed opaque abdominal muscles, white milky to buff mottling on the shell, and a pathognomonic runt-deformity syndrome. Histopathological examination of infected specimens revealed muscular edema, hemocyte infiltration, deformities, Zenker's necrosis, and eosinophilic intra-nuclear inclusion bodies (Cowdry type A). PCR results gave predictable amplicon sizes of 139 and 81 bp and confirmed the presence of IMNV and IHHNV with a total prevalence of 37.5 and 25%, respectively. A homology search by BLAST analysis showed that the retrieved isolates putatively belonged to IMNV and IHHNV based on 96.3 to 97% nucleotide identity to the corresponding open reading frame gene of each virus. The phylogenetic analysis clearly showed genetic similarity and cross-lineage between our isolates and other isolates from Egypt, the USA, Brazil, Indonesia, China, Korea, Taiwan, and Ecuador. In conclusion, gross inspection and histopathology may aid in the diagnosis of viral diseases; however, molecular tools are indispensable for confirming a possible infection. The current study recommends strict regulations during live shrimp transportation and implementing health control certificates over all imports and exports, especially in developing countries, including Egypt.

Transcriptome profiling in head kidney of rainbow trout (Oncorhynchus mykiss) after infection with the low-virulent Nagano genotype of infectious hematopoietic necrosis virus.

Infectious hematopoietic necrosis virus (IHNV) causes clinical diseases and mortality in a wide variety of salmonid species. Here, we studied transcriptional responses in rainbow trout infected by the IHNV-Nagano strain isolated in Korea. RNA-seq-based transcriptome analysis of head kidney tissues cataloged differentially expressed genes. Enrichment analysis of gene ontology annotations was performed, and a total of fifteen biological process terms were commonly identified at all time points. In the Kyoto Encyclopedia of Genes and Genomes pathway analysis, pathogen recognition receptor (PRR) signaling pathways such as the retinoic-acid-inducible gene-I-like receptor signaling pathway and the Toll-like receptor signaling pathway were identified at all time points. The nucleotide-binding oligomerization-domain-like receptor signaling pathway and cytosolic DNA-sensing pathway were identified at days 1 and 3. Protein-protein interaction network and centrality analyses revealed that the immune system, signaling molecules, and interaction pathways were upregulated at days 1 and 3, with the highest centrality of tumor necrosis factor. Cancer, cellular community, and endocrine system pathways were downregulated, with the highest centrality of fibronectin 1 at day 5. STAT1 was upregulated from days 1 to 5 with a high centrality. The reproducibility and repeatability of the transcriptome analysis were validated by RT-qPCR. IHNV-Nagano infection dynamically changed the transcriptome profiles in the head kidney of rainbow trout and induced a defense mechanism by regulating the immune and inflammatory pathways through PRR signaling at an early stage. Downregulated pathways involved in extracellular matrix formation and focal adhesion at day 5 indicated the possible failure of wound healing, which is important in the pathogenesis of IHNV infection.

First isolation and pathogenicity analysis of a genogroup U strain of infectious hematopoietic necrosis virus from rainbow trout in China.

Infectious hematopoietic necrosis virus (IHNV) is a major fish viral pathogen causing acute clinical disease and death in a variety of salmonids. IHNV isolates have been classified into five major genogroups according to the phylogenetic analysis of partial G gene fragments or the complete G gene sequence: U, M, E, L and J. Genogroup U strains have been reported in North America and Japan prior to 1982, and genogroup J is the only genogroup that has been reported in China. Here, one of IHNV strain (BjLL) was isolated from a local farm in China and were characterized in this study. The homogenate tissues of infected fry induced IHNV-positive cytopathic effects in epithelioma papulosum cyprinid (EPC) cells that were confirmed by RT-PCR and sequencing. The complete genome sequence of BjLL comprised 11,129 nucleotides, which had been submitted to GenBank (accession no. MF509592). By the sequence comparison and phylogenetic analysis for the G gene sequence of BjLL with 51 reference sequences in GenBank, we confirmed that this Chinese isolate belonged to genogroup U. Furthermore, virus exposure experiments with juvenile rainbow trout were conducted to assess the virulence and pathogenicity of BjLL. Compared with GS-2014 of genogroup J, BjLL was an obviously less virulent strain that could result in lower mortality. Besides, typical clinical symptoms and pathological damages could be seen in fish following infection of BjLL. The present study is the first report of genogroup U IHNV infection in China and will provide essential information for future studies on pathogenesis of IHNV BjLL and development of efficient control strategies.

Surveillance of disease incidence in shrimp farms located in the east coastal region of India and in vitro antibacterial efficacy of probiotics against Vibrio parahaemolyticus

We surveyed 130 shrimp farms located on the eastern coast of India to determine the prevalence of emerging diseases in Litopenaeus vannamei and Penaeus monodon. Live shrimps were collected from the farms based on external symptoms. The biochemical, molecular, and histopathology results confirmed infection with Enterocytozoon hepatopenaei (32.4%), Vibrio parahaemolyticus (27.7%), White Spot Syndrome Virus (25.4%), Vibrio alginolyticus (16.1%), Vibrio harveyi (13.1%), Monodon-type baculovirus (4.61%), and infectious Hematopoietic Necrosis Virus (2.3%) in the collected shrimps. Enterocytozoon hepatopenaei (EHP) occurred more frequently in L. vannamei than P. monodon, with the microsporidian spores in the hepatopancreas. In P. monodon, Monodon-type Baculovirus infection (33.3%) was dominant and small percentages of WSSV, IHHNV, V. alginolyticus, and V. harveyi were observed. A few ponds were observed with co-infection of EHP and WSSV (7.6%), V. parahaemolyticus and WSSV (4.6%) and also V. parahaemolyticus and EHP (6.1%). Among the Vibrio spp, V. parahaemolyticus showed the highest percentage of infection in L. vannamei. Overall, we found that shrimp were chiefly infected with EHP and V. parahaemolyticus. The impact of water quality parameters on shrimp diseases was not addressed in this study. In an antibiotic susceptibility study, V. parahaemolyticus isolated from L. vannamei ponds was susceptible to nitrofurantoin, chloramphenicol, oxytetracycline and tetracycline, but resistant to erythromycin and nalidixic acid. In a preliminary in vitro antibacterial activity assay, probiotics against V. parahaemolyticus showed high inhibitory activity and the results encourage further in-depth studies on the efficacy of probiotics for disease control and prevention in shrimp farms.

Reduced transmission of IHHNV to Penaeus monodon from shrimp pond wastewater filtered through a polychaete-assisted sand filter (PASF) system

A polychaete-assisted sand filter (PASF) can aid water recirculation systems for shrimp culture ponds by removing large amounts of nutrients and suspended solids and chemically treating wastewater. By ingesting and degrading organic matter, Perinereis helleri polychaetes reared in a PASF can accumulate and potentially remove infectious hypodermal and hematopoietic necrosis virus (IHHNV) present in wastewater from ponds rearing virus-infected Penaeus monodon shrimp. Reported here are data showing that filtering pond wastewater through a PASF reduces its potential to transmit IHHNV. The trial employed 3 groups of 4 tanks each containing 20 P. monodon randomly selected from a pond in which only low-level IHHNV infection was evident at moderate prevalence (IHHNV-low Pond 2). Over a 2 week period, each tank group was supplied with wastewater from either the same pond (Pond 2) or IHHNV-high Pond 1, in which IHHNV was 100% prevalent at ~104-fold higher infection loads, either directly or after being filtered through a PASF. IHHNV real-time qPCR data on total nucleic acid (TNA) extracted from pleopods of 35 P. monodon selected at random from each group identified an elevated IHHNV infection prevalence (91%) in shrimp tested from tanks supplied directly with wastewater from Pond 1. In comparison, IHHNV was detected at a much reduced prevalence and lower loads among shrimp tested from tanks supplied with wastewater from Pond 2 (33%) or from Pond 1 after it had been filtered through a PASF (31%). The IHHNV prevalence and load data indicate that a PASF can play a useful role in reducing the potential for shrimp pond wastewater to transmit IHHNV infection to naïve P. monodon.

A preliminary investigation on the mechanism of action of 4-(8-(2-ethylimidazole)octyloxy)-arctigenin against IHNV

Arctigenin derivatives form an elite class of naturally occurring compounds that possess promising antiviral therapeutic perspectives. In a previous study, we design and synthesize a arctigenin derivative, 4-(8-(2-ethylimidazole)octyloxy)-arctigenin (EOA), to evaluate its antiviral activity on infectious hematopoietic necrosis virus (IHNV). In this study, we find that the half maximal inhibitory concentrations (IC50) of EOA on IHNV nucleoprotein (N), phosphoprotein (P), matrix protein (M), nonvirion protein (NV) and polymerase (L) mRNA expression is 0.92, 0.80, 0.98, 0.89 and 0.87 μM, respectively. Mechanistically, our results show that EOA do not damage the viral particles directly, indicating EOA does not possess antiviral activity by destroying virions. Viral binding assays reveal that EOA do not interfere with IHNV adsorption. Because rapamycin has been shown to exhibit anti-IHNV activity by inducing autophagy of epithelioma papulosum cyprini (EPC) cells, we further investigate the relationship between EOA and autophagy in EPC cells. Autophagy fluorescence detection shows that EPC cells have a strong autophagy body after being treated with derivative EOA. The electron microscopy results show that EOA could induce typical autophagosomes which are representative structures of autophagy activation. Moreover, the punctate accumulation of green fluorescence-tagged microtubule-associate protein 1 light chain 3 (LC3) and the protein conversion from LC3-I to LC3-II are respectively confirmed by confocal fluorescence microscopy and western blotting. Overall, these findings demonstrate that EOA plays an anti-IHNV role via inducing autophagy in EPC cells.

Importance of sample size for estimating prevalence: a case example of infectious hematopoietic necrosis viral RNA detection in mixed-stock Fraser River sockeye salmon (Oncorhynchus nerka), British Columbia, Canada

Proper sample size must be considered when designing infectious-agent prevalence studies for mixed-stock fisheries, because bias and uncertainty complicate interpretation of apparent (test)-prevalence estimates. Sample size varies between stocks and are often smaller than expected during wild-salmonid surveys. Our case example of 2010–2016 survey of sockeye salmon (Oncorhynchus nerka) from different stocks of origin in British Columbia, Canada, illustrated the effect of sample size on apparent-prevalence interpretation. Molecular testing (viral RNA RT-qPCR) for infectious hematopoietic necrosis virus (IHNv) revealed large differences in apparent prevalence across wild salmon stocks (much higher from Chilko Lake) and sampling location (fresh water or marine), indicating differences in both stock and host life-stage effects. Ten of the 13 marine non-Chilko stock–years with IHNv-positive results had small sample sizes (&lt;30 samples per stock–year), which, with imperfect diagnostic tests (particularly lower diagnostic sensitivity), could lead to inaccurate apparent-prevalence estimation. When calculating sample size for expected apparent prevalence using different approaches, smaller sample sizes often led to decreased confidence in apparent-prevalence results and decreased power to detect a true difference from a reference value.

Japanese amberjack Seriola quinqueradiata and red sea bream Pagrus major susceptibility to infectious hematopoietic necrosis virus (IHNV) isolate.

Infectious hematopoietic necrosis virus (IHNV) is known as a causative agent of heavy mortalities in farmed rainbow trout. However, there is limited information on its virulence for marine fish species. In this study, Japanese amberjack Seriola quinqueradiata and red sea bream Pagrus major were experimentally infected by intraperitoneal (IP) injection and immersion, with an IHNV isolate from rainbow trout in Japan, to evaluate the virulence of the virus for these fish species. The cumulative mortality for immersed rainbow trout was 15%. IHNV was isolated from all dead fish and 50% of the sequentially sampled rainbow trout. When Japanese amberjack were challenged by IP injection and immersion, the resulting cumulative mortality was 70% and 0%, respectively. The virus was isolated from all dead fish and 1 out of 3 Japanese amberjack sampled at 9 d post exposure. However, no mortality was observed in either of the red sea bream groups challenged with IHNV. IHNV was not isolated from any of the surviving red sea bream, or from any of the sequentially sampled fish. The viral titer on Japanese amberjack-derived YTF cells was in the same log range as that on FHM and RTH-149 cells, but the titers on the red sea bream cell lines SBK and GBRS were lower than the other cell lines, and were significantly different from the FHM and RTH-149 cell lines. These results suggest that Japanese amberjack has a low susceptibility to IHNV, and red sea bream has no or little susceptibility to the virus.

INHV (Infectious Hematopoietic Necrosis Virus): Past, Present and Future

INHV (Infectious Hematopoietic Necrosis Virus): Past, Present and Future