Transcriptome Profiling of Oncorhynchus mykiss Infected with Low or Highly Pathogenic Viral Hemorrhagic Septicemia Virus (VHSV)

The rainbow trout (Oncorhynchus mykiss) is the most important produced species in freshwater within the European Union, usually reared in intensive farming systems. This species is highly susceptible to viral hemorrhagic septicemia (VHS), a severe systemic disease widespread globally throughout the world. Viral hemorrhagic septicemia virus (VHSV) is the etiological agent and, recently, three classes of VHSV virulence (high, moderate, and low) have been proposed based on the mortality rates, which are strictly dependent on the viral strain. The molecular mechanisms that regulate VHSV virulence and the stimulated gene responses in the host during infection are not completely unveiled. While some preliminary transcriptomic studies have been reported in other fish species, to date there are no publications on rainbow trout. Herein, we report the first time-course RNA sequencing analysis on rainbow trout juveniles experimentally infected with high and low VHSV pathogenic Italian strains. Transcriptome analysis was performed on head kidney samples collected at different time points (1, 2, and 5 days post infection). A large set of notable genes were found to be differentially expressed (DEGs) in all the challenged groups (e.s. trim63a, acod1, cox-2, skia, hipk1, cx35.4, ins, mtnr1a, tlr3, tlr7, mda5, lgp2). Moreover, the number of DEGs progressively increased especially during time with a greater amount found in the group infected with the high VHSV virulent strain. The gene ontology (GO) enrichment analysis highlighted that functions related to inflammation were modulated in rainbow trout during the first days of VHSV infection, regardless of the pathogenicity of the strain. While some functions showed slight differences in enrichments between the two infected groups, others appeared more exclusively modulated in the group challenged with the highly pathogenic strain.

Tilapia lake virus: A structured phylogenetic approach

Tilapia Lake Virus (TiLV), also known as Tilapia tilapinevirus, is an emerging pathogen affecting both wild and farmed tilapia (Oreochromis spp.), which is considered one of the most important fish species for human consumption. Since its first report in Israel in 2014, Tilapia Lake Virus has spread globally causing mortality rates up to 90%. Despite the huge socio-economic impact of this viral species, to date the scarce availability of Tilapia Lake Virus complete genomes is severely affecting the knowledge on the origin, evolution and epidemiology of this virus. Herein, along with the identification, isolation and complete genome sequencing of two Israeli Tilapia Lake Virus deriving from outbreaks occurred in tilapia farms in Israel in 2018, we performed a bioinformatics multifactorial approach aiming to characterize each genetic segment before carrying out phylogenetic analysis. Results highlighted the suitability of using the concatenated ORFs 1, 3, and 5 in order to obtain the most reliable, fixed and fully supported tree topology. Finally, we also attempted to investigate the presence of potential reassortment events in all the studied isolates. As a result, we report a reassortment event detected in segment 3 of isolate TiLV/Israel/939-9/2018 involved in the present study, and confirmed almost all the other events previously reported.

Investigating the physiological response and antibody concentration of gilthead sea bream (Sparus aurata) following Vibrio anguillarum vaccination depending on the stress coping style

Stress coping styles (SCSs) are defined as coherent sets of individual physiological and behavioral differences in stress response consistent across time and context and are described in a wide range of taxa, including fishes. These differences in behavior and physiology are of great interest because they may have direct implications on animal health, welfare, and performance in farming systems, including aquaculture. In this study, the physiological responses of sea bream (Sparus aurata) from different SCSs following Vibrio anguillarum vaccination were monitored. Fish were first screened either bold or shy (proxy of proactive and reactive SCSs, respectively) using group risk-taking tests and were then injected with a vaccine against V. anguillarum. Following vaccination, the fish were implanted with an accelerometer tag to monitor their swimming activity (proxy of energy expenditure), and blood sampling was carried out to measure health and welfare parameters (e.g., cortisol, glucose, hemoglobin) and aspecific immunity (e.g., protease, total proteins). In addition, blood was also collected at three different sampling times to screen antibody levels and, thus, to evaluate the efficiency of the vaccine. Following vaccination, bold fish displayed lower swimming activity values, indicative of lower energy expenditure, and also displayed higher levels of hematocrit, total proteins, and lysozyme in the plasma than the shy ones, which could be indicative of better health/welfare status and greater aspecific immunity. Finally, the V. anguillarum vaccination appeared to be more efficient in bold fish since the number of total antibodies was found higher than in shy fish 1 month after vaccination. Such results could help improve both health/welfare and productivity of farmed sea breams by selecting more robust fish, better adapted to farming conditions.

Role of Rotifers in Betanodavirus Transmission to European Sea Bass Larvae

Marine invertebrates such as rotifers or Artemia, frequently used for fish larvae feeding, can be a potential source of pathogens. It has been demonstrated that Artemia can act as a nervous necrosis virus (NNV)-vector to Senegalese sole larvae. Therefore, in this study, we aimed to clarify the role of rotifers in NNV transmission to sea bass larvae following an oral challenge. Our results showed that sea bass larvae fed on a single dose of rotifers retaining NNV displayed clinical signs, mortality, and viral replication similar to the immersion challenge, although the course of the infection was slightly different between the two infection routes. Furthermore, we also demonstrated that rotifers can internalize NNV particles due to their filtering nature and maintain virus viability since viral particles were detected by immunohistochemistry, immunofluorescence, and cell culture within the rotifer body. However, viral quantification data suggested that rotifers are not permissive to NNV replication. In conclusion, this research demonstrated NNV horizontal transmission through rotifers to sea bass larvae, highlighting the importance of establishing strict routine controls on live food to prevent the introduction of potential pathogens to hatcheries.

Increased virulence of Italian infectious hematopoietic necrosis virus (IHNV) associated with the emergence of new strains

Infectious hematopoietic necrosis virus (IHNV) is the causative agent of IHN triggering a systemic syndrome in salmonid fish. Although IHNV has always been associated with low levels of mortality in Italian trout farming industries, in the last years trout farmers have experienced severe disease outbreaks. However, the observed increasing virulence of IHNV is still based on empirical evidence due to the poor and often confounding information from the field. Virulence characterization of a selection of sixteen Italian isolates was performed through in vivo challenge of juvenile rainbow trout to confirm field evidence. The virulence of each strain was firstly described in terms of cumulative mortality and survival probability estimated by Kaplan-Meier curves. Furthermore, parametric survival models were applied to analyze the mortality rate profiles. Hence, it was possible to characterize the strain-specific mortality peaks and to relate their topology to virulence and mortality. Indeed, a positive correlation between maximum mortality probability and virulence was observed for all the strains. Results also indicate that more virulent is the strain, the earliest and narrowest is the mortality peak. Additionally, intra-host viral quantification determined in dead animals showed a significant correlation between viral replication and virulence. Whole-genome phylogeny conducted to determine whether there was a relation between virulence phenotype and IHNV genetics evidenced no clear clustering according to phenotype. Moreover, a root-to-tip analysis based on genetic distances and sampling date of Italian IHNV isolates highlighted a relevant temporal signal indicating an evolving nature of the virus, over time, with the more virulent strains being the more recent ones. This study provides the first systematic characterization of Italian IHNV's virulence. Overall results confirm field data and point out an abrupt increase in IHNV virulence, with strains from 2015-2019 showing moderate to high virulence in rainbow trout. Further investigations are needed in order to extensively clarify the relation between evolution and virulence of IHNV and investigate the genetic determinants of virulence of this viral species in rainbow trout.

Lumpfish (Cyclopterus lumpus, Linnaeus) is susceptible to viral nervous necrosis: Result of an experimental infection with different genotypes of Betanodavirus

In recent years, the use of cleaner fish for biological control of sea lice has increased considerably. Along with this, a number of infectious diseases have emerged. The aim of this study was to investigate the susceptibility of lumpfish (Cyclopterus lumpus) to Betanodavirus since it was detected in asymptomatic wild wrasses in Norway and Sweden. Three betanodaviruses were used to challenge lumpfish: one RGNNV genotype and two BFNNV genotypes. Fish were injected and monitored for 4 weeks. Brain samples from clinically affected specimens, from weekly randomly selected fish and survivors were subjected to molecular testing, viral isolation, histopathology and immunohistochemistry. Reduced survival was observed but was attributed to tail-biting behaviour, since no nervous signs were observed throughout the study. Betanodavirus RNA was detected in all samples, additionally suggesting an active replication of the virus in the brain. Viral isolation confirmed molecular biology results and revealed a high viral titre in BFNNV-infected groups associated with typical lesions in brains and eyes of survivor fish. We concluded that lumpfish are susceptible to Betanodavirus, as proven by the high viral titre and brain lesions detected, but further studies are necessary to understand if Betanodavirus can cause clinical disease in this species.

Lack of in vivo cross-protection of two different betanodavirus species RGNNV and SJNNV in European sea bass Dicentrachus labrax

Viral encephalopathy and retinopathy (VER) is a severe infective disease characterized by neuropathological changes in several fish species associated with high mortality. The etiological agent is a virus belonging to the Nodaviridae family, genus Betanodavirus. To date, four different betanodavirus species have been officially recognized by International Committee on Taxonomy of Viruses (ICTV), namely the red-spotted grouper- (RGNNV), the striped jack- (SJNNV), the barfin flounder- (BFNNV) and the tiger puffer nervous necrosis virus (TPNNV). Moreover, two reassortants RGNNV/SJNNV and SJNNV/RGNNV have been described. Betanodaviruses can be classified into three different serotypes (A, B and C) that are antigenically different, so none (between serotype A and C) or partial (between serotype B and C) cross-immunoreactivity has been detected in vitro. In this study we investigated the in vivo cross-protection of the two main betanodavirus species (RGNNV and SJNNV), which belong to distinct serotype, by immunizing intraperitoneally (IP) juvenile sea bass with formalin inactivated RGNNV and SJNNV vaccines, followed by a challenge with RGNNV. Fish IP vaccinated with inactivated RGNNV showed a high protection value (85%). Serological analyses highlighted a great specific anti-NNV immunoglobulin M (IgM) production against the homologous virus, while a good seroconversion with low neutralization property was highlighted against the heterologous virus. In fish IP vaccinated with inactivated SJNNV the protection recorded was equal to 25%, significantly lower respect to the one provided by RGNNV IP vaccine. ELISA test detected good IgM production against the homologous virus, and a lower, but still detectable IgM production against the heterologous one. By contrast, serum neutralization test highlighted a poorly detectable antibody production unable to neutralize either the homologous or the heterologous virus. These results confirm that the two serotypes are not cross-protective in vivo. According to these findings, the production of multivalent formulation, or at least the provision of different types of vaccines based on both fish and virus species requirement, should be recommended in order to broaden the range of protection.

Detection and characterization of a rhabdovirus causing mortality in black bullhead catfish, Ameiurus melas

This study fully describes a severe disease outbreak occurred in 2016 in black bullhead catfish farmed in Italy. Affected fish showed nervous clinical signs as well as emaciations and haemorrhagic petechiae on the skin at the fin bases, abdomen and gills. Viral isolation in cell culture allowed the subsequent identification of a rhabdovirus, tentatively named ictalurid rhabdovirus (IcRV), through electron microscopy, immunofluorescence and whole genome sequencing (WGS). The newly isolated virus, together with 14 additional viral strains stored in our repository and detected during similar mortality episodes in the period 1993-2016, was phylogenetically analysed on the basis of the nucleoprotein and the glycoprotein nucleotide and amino acid sequences. The genetic distances among Italian IcRV strains were also estimated. Our results show that all the IcRV strains belong to the genus Sprivivirus and are closely related to the tench rhabdovirus (TenRV). Italian catfish production is constantly decreasing, mainly due to viral infections, which include the newly characterized IcRV. Data presented in this work will assist to investigate the molecular epidemiology and the diffusive dynamics of this virus and to develop adequate surveillance activities.

Viral nervous necrosis in gilthead sea bream (Sparus aurata) caused by reassortant betanodavirus RGNNV/SJNNV: an emerging threat for Mediterranean aquaculture

Viral nervous necrosis (VNN) certainly represents the biggest challenge for the sustainability and the development of aquaculture. A large number of economically relevant fish species have proven to be susceptible to the disease. Conversely, gilthead sea bream has generally been considered resistant to VNN, although it has been possible to isolate the virus from apparently healthy sea bream and sporadically from affected larvae and postlarvae. Unexpectedly, in 2014–2016 an increasing number of hatcheries in Europe have experienced mass mortalities in sea bream larvae. Two clinical outbreaks were monitored over this time span and findings are reported in this paper. Despite showing no specific clinical signs, the affected fish displayed high mortality and histological lesions typical of VNN. Fish tested positive for betanodavirus by different laboratory techniques. The isolates were all genetically characterized as being reassortant strains RGNNV/SJNNV. A genetic characterization of all sea bream betanodaviruses which had been isolated in the past had revealed that the majority of the strains infecting sea bream are actually RGNNV/SJNNV. Taken together, this information strongly suggests that RGNNV/SJNNV betanodavirus possesses a particular tropism to sea bream, which can pose a new and unexpected threat to the Mediterranean aquaculture.

Efficacy of domestic cooking inactivation of human hepatitis A virus in experimentally infected manila clams (Ruditapes philippinarum)

AIM

The aim of this work was to evaluate the efficacy of domestic cooking in inactivating Manila clams experimentally infected with human hepatitis A virus (HAV).

METHODS AND RESULTS

Electronic temperature probes were positioned to measure the internal temperature of Manila clams during domestic cooking. Two batches were infected with 10(7) and 10(5) TCID50  ml(-1) of HAV. The infected whole-in-shell clams were divided into three replicates and cooked on a conventional stove both singularly and in group and removed from the pan at fixed intervals. Pools of three digestive glands were examined by virus isolation for three blind passages and cell culture supernatant tested with real-time PCR.

CONCLUSION

Results showed that 2-min cooking by a traditional domestic method at a temperature close to 100°C, after the opening up of the valves of all the clams, can completely devitalize the HAV in high viral load-infected clams.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study on inactivation of HAV in experimentally infected Manila clams subjected to domestic cooking. At present, labelling all lagoon products as 'requiring cooking before consumption' is highly recommended, but no specifications are given on how long and at what temperature they should be cooked. Considering the high commercial value of Manila clams, our results can provide both the producers and the consumer with useful indications on how to cook clams to prevent the risk of HAV foodborne illness.

Infectivity of H7 LP and HP influenza viruses at different temperatures and pH and persistence of H7 HP virus in poultry meat at refrigeration temperature

The aims of this study were to assess the infectivity of highly pathogenic (HP) and low pathogenicity (LP) H7 AI viruses at different temperatures and pH values and to investigate the persistance of HP H7 virus in chicken, turkey and duck meat. The H7 viruses tested remained infectious at +4°C and +20°C for 200 and >50 days, respectively. At pH 5, H7 viruses retained their infectivity for a shorter period of time compared to pH 7. The infectivity of HP H7 was detected >2 months in meat maintained at +4°C and was higher in chicken meat compared to turkey and duck meat. Results of this study show that higher temperatures and lower pH values both reduce virus infectivity and demonstrate that HP H7 virus can remain infectious in meat for extended periods of time.

Antigenic drift in H5N1 avian influenza virus in poultry is driven by mutations in major antigenic sites of the hemagglutinin molecule analogous to those for human influenza virus

H5N1 highly pathogenic avian influenza virus has been endemic in poultry in Egypt since 2008, notwithstanding the implementation of mass vaccination and culling of infected birds. Extensive circulation of the virus has resulted in a progressive genetic evolution and an antigenic drift. In poultry, the occurrence of antigenic drift in avian influenza viruses is less well documented and the mechanisms remain to be clarified. To test the hypothesis that H5N1 antigenic drift is driven by mechanisms similar to type A influenza viruses in humans, we generated reassortant viruses, by reverse genetics, that harbored molecular changes identified in genetically divergent viruses circulating in the vaccinated population. Parental and reassortant phenotype viruses were antigenically analyzed by hemagglutination inhibition (HI) test and microneutralization (MN) assay. The results of the study indicate that the antigenic drift of H5N1 in poultry is driven by multiple mutations primarily occurring in major antigenic sites at the receptor binding subdomain, similarly to what has been described for human influenza H1 and H3 subtype viruses.