Ganglioneuritis causing high mortalities in farmed Australian abalone (Haliotis laevigata and Haliotis rubra)

Mechanisms of HAHV-1 Interaction with Hemocytes in Haliotis diversicolor supertexta: An In Vitro Study

Haliotid herpesvirus 1 (HAHV-1) causes significant damage to the abalone aquaculture industry. Knowledge of HAHV-1 invasion and host defense mechanisms is limited due to the lack of stable molluscan cell lines. The present study established an in vitro infection model of HAHV-1 using the primary suspension cultures of hemocytes from Haliotis diversicolor supertexta and Haliotis discus hannai. The cytopathic effects of HAHV-1 on adherent-cultured hemocytes of both species were also investigated. The HAHV-1 DNA loads were firstly monitored by means of quantitative PCR during the development of viral infection, and subsequently the mechanism of interaction between HAHV-1 and hemocytes was explored by means of a transcriptome analysis. H. diversicolor supertexta hemocytes exhibited a high degree of susceptibility to HAHV-1, with viral loads reaching a peak of 4.0 × 10⁷ copies/ng DNA. In contrast, no significant replication was observed in H. discus hannai hemocytes. Transcriptome analysis revealed that HAHV-1 evades the host immune response in the early stages of infection, and hijacks the host's energy and redox metabolism to promote its replication at the late stages. Consequently, this study provides a valuable reference point for the investigation of virus-host interaction between HAHV-1 and abalone in vitro.

A widespread picornavirus affects the hemocytes of the noble pen shell (Pinna nobilis), leading to its immunosuppression

Introduction

The widespread mass mortality of the noble pen shell (Pinna nobilis) has occurred in several Mediterranean countries in the past 7 years. Single-stranded RNA viruses affecting immune cells and leading to immune dysfunction have been widely reported in human and animal species. Here, we present data linking P. nobilis mass mortality events (MMEs) to hemocyte picornavirus (PV) infection. This study was performed on specimens from wild and captive populations.

Methods

We sampled P. nobilis from two regions of Spain [Catalonia (24 animals) and Murcia (four animals)] and one region in Italy [Venice (6 animals)]. Each of them were analyzed using transmission electron microscopy (TEM) to describe the morphology and self-assembly of virions. Illumina sequencing coupled to qPCR was performed to describe the identified virus and part of its genome.

Results and discussion

In 100% of our samples, ultrastructure revealed the presence of a virus (20 nm diameter) capable of replicating within granulocytes and hyalinocytes, leading to the accumulation of complex vesicles of different dimensions within the cytoplasm. As the PV infection progressed, dead hemocytes, infectious exosomes, and budding of extracellular vesicles were visible, along with endocytic vesicles entering other cells. The THC (total hemocyte count) values observed in both captive (eight animals) (3.5 × 104-1.60 × 105 ml-1 cells) and wild animals (14 samples) (1.90-2.42 × 105 ml-1 cells) were lower than those reported before MMEs. Sequencing of P. nobilis (six animals) hemocyte cDNA libraries revealed the presence of two main sequences of Picornavirales, family Marnaviridae. The highest number of reads belonged to animals that exhibited active replication phases and abundant viral particles from transmission electron microscopy (TEM) observations. These sequences correspond to the genus Sogarnavirus-a picornavirus identified in the marine diatom Chaetoceros tenuissimus (named C. tenuissimus RNA virus type II). Real-time PCR performed on the two most abundant RNA viruses previously identified by in silico analysis revealed positive results only for sequences similar to the C. tenuissimus RNA virus. These results may not conclusively identify picornavirus in noble pen shell hemocytes; therefore, further study is required. Our findings suggest that picornavirus infection likely causes immunosuppression, making individuals prone to opportunistic infections, which is a potential cause for the MMEs observed in the Mediterranean.

The Role of Anti-Viral Effector Molecules in Mollusc Hemolymph

Molluscs are major contributors to the international and Australian aquaculture industries, however, their immune systems remain poorly understood due to limited access to draft genomes and evidence of divergences from model organisms. As invertebrates, molluscs lack adaptive immune systems or 'memory', and rely solely on innate immunity for antimicrobial defence. Hemolymph, the circulatory fluid of invertebrates, contains hemocytes which secrete effector molecules with immune regulatory functions. Interactions between mollusc effector molecules and bacterial and fungal pathogens have been well documented, however, there is limited knowledge of their roles against viruses, which cause high mortality and significant production losses in these species. Of the major effector molecules, only the direct acting protein dicer-2 and the antimicrobial peptides (AMPs) hemocyanin and myticin-C have shown antiviral activity. A better understanding of these effector molecules may allow for the manipulation of mollusc proteomes to enhance antiviral and overall antimicrobial defence to prevent future outbreaks and minimize economic outbreaks. Moreover, effector molecule research may yield the description and production of novel antimicrobial treatments for a broad host range of animal species.

Diseases of Gastropoda

Gastropods (class Gastropoda) form the largest of the classes in the phylum Mollusca and inhabit terrestrial, fresh water and marine environments. A large number of these species are of major conservation importance and are an essential component of ecosystems. Gastropods may be deemed as pests, having a negative impact in horticulture and agriculture, whereas others may be used as a food source for human consumption and therefore are beneficial. Gastropods are susceptible to primary diseases and also act as intermediate hosts for diseases which affect other animals, including humans. The diseases described include two that are notifiable to the World Organisation for Animal Health (OIE): Xenohaliotis californiensis and Abalone viral ganglioneuritis caused by Haliotid herpesvirus-1 (HaHV-1). Research into the diseases of gastropods has often focused on those species that act as intermediate disease hosts, those that are used in research or those cultured for food. In this paper we review the viral, bacterial, fungal, parasitic and miscellaneous conditions that have been reported in gastropods and mention some of the factors that appear to predispose them to disease. The pathogenicity of a number of these conditions has not been fully ascertained and more research is needed into specifying both the etiological agent and significance in some of the diseases reported.

Susceptibility of Four Abalone Species, Haliotis gigantea, Haliotis discus discus, Haliotis discus hannai and Haliotis diversicolor, to Abalone asfa-like Virus

Abalone amyotrophia is a viral disease that causes mass mortality of juvenile Haliotis discus and H. madaka. Although the cause of this disease has yet to be identified, we had previously postulated a novel virus with partial genome sequence similarity to that of African swine fever virus is the causative agent and proposed abalone asfa-like virus (AbALV) as a provisional name. In this study, three species of juvenile abalone (H. gigantea, H. discus discus, and H. diversicolor) and four species of adult abalone (the above three species plus H. discus hannai) were experimentally infected, and their susceptibility to AbALV was investigated by recording mortality, quantitatively determining viral load by PCR, and conducting immunohistological studies. In the infection test using 7-month-old animals, H. gigantea, which was previously reported to be insusceptible to the disease, showed multiplication of the virus to the same extent as in H. discus discus, resulting in mass mortality. H. discus discus at 7 months old showed abnormal cell masses, notches in the edge of the shell and brown pigmentation inside of the shell, which are histopathological and external features of this disease, while H. gigantea did not show any of these characteristics despite suffering high mortality. Adult abalones had low mortality and viral replication in all species; however, all three species, except H. diversicolor, became carriers of the virus. In immunohistological observations, cells positive for viral antigens were detected predominantly in the gills of juvenile H. discus discus and H. gigantea, and mass mortality was observed in these species. In H. diversicolor, neither juvenile nor adult mortality from infection occurred, and the AbALV genome was not increased by experimental infection through cohabitation or injection. Our results suggest that H. gigantea, H. discus discus and H. discus hannai are susceptible to AbALV, while H. diversicolor is not. These results confirmed that AbALV is the etiological agent of abalone amyotrophia.

Viral Decoys: The Only Two Herpesviruses Infecting Invertebrates Evolved Different Transcriptional Strategies to Deflect Post-Transcriptional Editing

The highly versatile group of Herpesviruses cause disease in a wide range of hosts. In invertebrates, only two herpesviruses are known: the malacoherpesviruses HaHV-1 and OsHV-1 infecting gastropods and bivalves, respectively. To understand viral transcript architecture and diversity we first reconstructed full-length viral genomes of HaHV-1 infecting Haliotis diversicolor supertexta and OsHV-1 infecting Scapharca broughtonii by DNA-seq. We then used RNA-seq over the time-course of experimental infections to establish viral transcriptional dynamics, followed by PacBio long-read sequencing of full-length transcripts to untangle viral transcript architectures at two selected time points. Despite similarities in genome structure, in the number of genes and in the diverse transcriptomic architectures, we measured a ten-fold higher transcript variability in HaHV-1, with more extended antisense gene transcription. Transcriptional dynamics also appeared different, both in timing and expression trends. Both viruses were heavily affected by post-transcriptional modifications performed by ADAR1 affecting sense-antisense gene pairs forming dsRNAs. However, OsHV-1 concentrated these modifications in a few genomic hotspots, whereas HaHV-1 diluted ADAR1 impact by elongated and polycistronic transcripts distributed over its whole genome. These transcriptional strategies might thus provide alternative potential roles for sense-antisense transcription in viral transcriptomes to evade the host's immune response in different virus-host combinations.

Analysis of the Curative Effect of Neoadjuvant Therapy on Pancreatic Cancer

The prevalence of pancreatic cancer is sharply increasing recently, which significantly increases the economic burden of the population. At present, the primary treatment of resectable pancreatic cancer is surgical resection, followed by chemotherapy with or without radiation. However, the recurrence rates remain high even after R0 resection. This treatment strategy does not distinguish undetected metastatic disease, and it is prone to postoperative complications. Neoadjuvant therapies, including neoadjuvant chemotherapy and radiotherapy, is being increasingly utilized in borderline resectable as well as resectable pancreatic cancer. This review summarized and discussed clinical trials of neoadjuvant therapy for pancreatic cancer, comparing resection rates, outcome measures, and adverse reactions between neoadjuvant chemotherapy and neoadjuvant chemoradiotherapy.

A rapid phenotype change in the pathogen Perkinsus marinus was associated with a historically significant marine disease emergence in the eastern oyster

The protozoan parasite Perkinsus marinus, which causes dermo disease in Crassostrea virginica, is one of the most ecologically important and economically destructive marine pathogens. The rapid and persistent intensification of dermo in the USA in the 1980s has long been enigmatic. Attributed originally to the effects of multi-year drought, climatic factors fail to fully explain the geographic extent of dermo’s intensification or the persistence of its intensified activity. Here we show that emergence of a unique, hypervirulent P. marinus phenotype was associated with the increase in prevalence and intensity of this disease and associated mortality. Retrospective histopathology of 8355 archival oysters from 1960 to 2018 spanning Chesapeake Bay, South Carolina, and New Jersey revealed that a new parasite phenotype emerged between 1983 and 1990, concurrent with major historical dermo disease outbreaks. Phenotypic changes included a shortening of the parasite’s life cycle and a tropism shift from deeper connective tissues to digestive epithelia. The changes are likely adaptive with regard to the reduced oyster abundance and longevity faced by P. marinus after rapid establishment of exotic pathogen Haplosporidium nelsoni in 1959. Our findings, we hypothesize, illustrate a novel ecosystem response to a marine parasite invasion: an increase in virulence in a native parasite.

Abalone Viral Ganglioneuritis

Abalone viral ganglioneuritis (AVG), caused by Haliotid herpesvirus-1 (HaHV-1; previously called abalone herpesvirus), is a disease that has been responsible for extensive mortalities in wild and farmed abalone and has caused significant economic losses in Asia and Australia since outbreaks occurred in the early 2000s. Researchers from Taiwan, China, and Australia have conducted numerous studies encompassing HaHV-1 genome sequencing, development of molecular diagnostic tests, and evaluation of the susceptibility of various abalone species to AVG as well as studies of gene expression in abalone upon virus infection. This review presents a timeline of the most significant research findings on AVG and HaHV-1 as well as potential future research avenues to further understand this disease in order to develop better management strategies.

Immune Control of Herpesvirus Infection in Molluscs

Molluscan herpesviruses that are capable of infecting economically important species of abalone and oysters have caused significant losses in production due to the high mortality rate of infected animals. Current methods in preventing and controlling herpesviruses in the aquacultural industry are based around biosecurity measures which are impractical and do not contain the virus as farms source their water from oceans. Due to the lack of an adaptive immune system in molluscs, vaccine related therapies are not a viable option; therefore, a novel preventative strategy known as immune priming was recently explored. Immune priming has been shown to provide direct protection in oysters from Ostreid herpesvirus-1, as well as to their progeny through trans-generational immune priming. The mechanisms of these processes are not completely understood, however advancements in the characterisation of the oyster immune response has assisted in formulating potential hypotheses. Limited literature has explored the immune response of abalone infected with Haliotid herpesvirus as well as the potential for immune priming in these species, therefore, more research is required in this area to determine whether this is a practical solution for control of molluscan herpesviruses in an aquaculture setting.

In situ hybridization revealed wide distribution of Haliotid herpesvirus 1 in infected small abalone, Haliotis diversicolor supertexta

Ganglioneuritis was the primary pathologic change in infected abalone associated with Haliotid herpesvirus 1 (HaHV-1) infection, which eventually became known as abalone viral ganglioneuritis (AVG). However, the distribution of HaHV-1 in the other tissues and organs of infected abalone has not been systemically investigated. In the present study, the distribution of HaHV-1-CN2003 variant in different organs of small abalone, Haliotis diversicolor supertexta, collected at seven different time points post experimental infection, was investigated with histopathological examination and in situ hybridization (ISH) of HaHV-1 DNA. ISH signals were first observed in pedal ganglia at 48 h post injection, and were consistently observed in this tissue of challenged abalone. At the same time, increased cellularity accompanied by ISH signals was observed in some peripheral ganglia of mantle and kidney. At the end of infection period, lesions and co-localized ISH signals in infiltrated cells were detected occasionally in the mantle and hepatopancreas. Transmission electron microscope analysis revealed the presence of herpes-like viral particles in haemocyte nuclei of infected abalone. Our results indicated that, although HaHV-1-CN2003 was primarily neurotropic, it could infect other tissues including haemocytes.

A novel Asfarvirus-like virus identified as a potential cause of mass mortality of abalone

A novel Asfarvirus-like virus is proposed as the etiological agent responsible for mass mortality in abalone. The disease, called abalone amyotrophia, originally was recognized in the 1980s, but efforts to identify a causative agent were unsuccessful. We prepared a semi-purified fraction by nuclease treatment and ultracentrifugation of diseased abalone homogenate, and the existence of the etiological agent in the fraction was confirmed by a challenge test. Using next-generation sequencing and PCR-based epidemiological surveys, we obtained a partial sequence with similarity to a member of the family Asfarviridae. BLASTP analysis of the predicted proteins against a virus database resulted in 48 proteins encoded by the novel virus with top hits against proteins encoded by African swine fever virus (ASFV). Phylogenetic analyses of predicted proteins of the novel virus confirmed that ASFV represents the closest relative. Comparative genomic analysis revealed gene-order conservation between the novel virus and ASFV. In situ hybridization targeting the gene encoding the major capsid protein of the novel virus detected positive signals only in tissue from diseased abalone. The results of this study suggest that the putative causative agent should be considered a tentative new member of the family Asfarviridae, which we provisionally designate abalone asfa-like virus (AbALV).

Diagnostic test accuracy when screening for Haliotid herpesvirus 1 (AbHV) in apparently healthy populations of Australian abalone Haliotis spp

The accuracy of 3 real-time PCR assays (ORF49, ORF66 and ORF77) and histopathology was evaluated for the purpose of demonstrating or certifying abalone free from Haliotid herpesvirus 1 (AbHV), the causative agent of abalone viral ganglioneuritis. Analytically, all 3 qPCRs showed equivalent limit of detection (20 copies per reaction); however, ORF49 could not detect 2 of the AbHV genotypes. A selection of 1452 archive specimens sourced from apparently healthy abalone populations was screened using all 4 tests. In the absence of a perfect reference standard, a Bayesian latent class analysis was built to estimate diagnostic sensitivity (DSe), diagnostic specificity (DSp) and likelihood ratios of a positive (LR+) and negative test result (LR-) for each individual test and for all possible combinations of test pairs interpreted either in series or in parallel. The pair ORF49/ORF66 interpreted in parallel performed the best both analytically and diagnostically to demonstrate freedom from AbHV in an established population of abalone and to certify individual abalone free from AbHV for trade or movement purposes (DSe = 96.0%, 95% posterior credibility interval [PCI]: 82.6 to 99.9; DSp = 97.7%, 95% PCI: 96.4 to 99.4; LR+ = 41.4, 95% PCI: 27.4 to 148.7; LR- = 0.041, 95% PCI: 0.001 to 0.176). Histopathology showed very poor DSe (DSe = 6.3%, 95% PCI: 2.4 to 13.1) as expected since most infected abalone in the study were likely sub-clinical with limited pathological change. Nevertheless, we recommend histopathology when clinically investigating outbreaks to find potential, new, emerging AbHV genotype(s) that may not be detectable by either ORF49 or ORF66.

Investigating the natural resistance of blackfoot p-a%%KERN_ERR%%ua Haliotis iris to abalone viral ganglioneuritis using whole transcriptome analysis

The natural resistance of New Zealand blackfoot p-a%%%%%%%%%%%%%%KERN_ERR%%KERN_ERR%%KERN_ERR%%KERN_ERR%%KERN_ERR%%KERN_ERR%%KERN_ERR%%ua Haliotis iris to infection by haliotid herpesvirus-1 (HaHV-1) and to the disease abalone viral ganglioneuritis was investigated in experimentally challenged p-aua using high throughput RNA-sequencing. HaHV-1-challenged p-aua up-regulated broad classes of genes that contained chitin-binding peritrophin-A domains, which seem to play diverse roles in the p-aua immune response. The p-aua also up-regulated vascular adhesion protein-1 (VAP-1), an important adhesion molecule for lymphocytes, and chitotriosidase-1 (CHIT-1), an immunologically important gene in mammalian immune systems. Moreover, several blood coagulation pathways were dysregulated in the p-aua, possibly indicating viral modulation. We also saw several indications that neurological tissues were specifically affected by HaHV-1, including the dysregulation of beta-1,4-N-acetylgalactosaminyltransferase (B4GALNT), GM2 ganglioside, neuroligin-4 and the Notch signalling pathway. This research may support the development of molecular therapeutics useful to control and/or manage viral outbreaks in abalone culture.

Dual Transcriptomic Analysis Reveals a Delayed Antiviral Response of Haliotis diversicolor supertexta against Haliotid Herpesvirus-1

Haliotid herpesvirus-1 (HaHV-1) is the first identified gastropod herpesvirus, causing a highly lethal neurologic disease of abalone species. The genome of HaHV-1 has been sequenced, but the functions of the putative genes and their roles during infection are still poorly understood. In the present study, transcriptomic profiles of Haliotis diversicolor supertexta at 0, 24 and 60 h post injection (hpi) with HaHV-1 were characterized through high-throughput RNA sequencing. A total of 448 M raw reads were obtained and assembled into 2.08 × 10⁵ unigenes with a mean length of 1486 bp and an N50 of 2455 bp. Although we detected increased HaHV-1 DNA loads and active viral expression at 24 hpi, this evidence was not linked to significant changes of host transcriptomic profiles between 0 and 24 hpi, whereas a rich immune-related gene set was over-expressed at 60 hpi. These results indicate that, at least at the beginning of HaHV-1 infection, the virus can replicate with no activation of the host immune response. We propose that HaHV-1 may evolve more effective strategies to modulate the host immune response and hide during replication, so that it could evade the immune surveillance at the early stage of infection.

RNA-seq of HaHV-1-infected abalones reveals a common transcriptional signature of Malacoherpesviruses

Haliotid herpesvirus-1 (HaHV-1) is the viral agent causative of abalone viral ganglioneuritis, a disease that has severely affected gastropod aquaculture. Although limited, the sequence similarity between HaHV-1 and Ostreid herpesvirus-1 supported the assignment of both viruses to Malacoherpesviridae, a Herpesvirales family distantly related with other viruses. In this study, we reported the first transcriptional data of HaHV-1, obtained from an experimental infection of Haliotis diversicolor supertexta. We also sequenced the genome draft of the Chinese HaHV-1 variant isolated in 2003 (HaHV-1-CN2003) by PacBio technology. Analysis of 13 million reads obtained from 3 RNA samples at 60 hours post injection (hpi) allowed the prediction of 51 new ORFs for a total of 117 viral genes and the identification of 207 variations from the reference genome, consisting in 135 Single Nucleotide Polymorphisms (SNPs) and 72 Insertions or Deletions (InDels). The pairing of genomic and transcriptomic data supported the identification of 60 additional SNPs, representing viral transcriptional variability and preferentially grouped in hotspots. The expression analysis of HaHV-1 ORFs revealed one putative secreted protein, two putative capsid proteins and a possible viral capsid protease as the most expressed genes and demonstrated highly synchronized viral expression patterns of the 3 infected animals at 60 hpi. Quantitative reverse transcription data of 37 viral genes supported the burst of viral transcription at 30 and 60 hpi during the 72 hours of the infection experiment, and allowed the distinction between early and late viral genes.

Susceptibility of two abalone species, Haliotis diversicolor supertexta and Haliotis discus hannai, to Haliotid herpesvirus 1 infection

Abalone viral ganglioneuritis (AVG), caused by Haliotid herpesvirus-1 (HaHV-1) infection, has been reported as the main cause of mortality and heavy losses of wild and cultivated abalone in Taiwan and Australia since 2003. HaHV-1 DNA has also been reported in diseased abalone collected in early 2000s in China. However, no data is available about the susceptibility, disease process and pathological changes of HaHV-1 infection in the primary cultivated abalone species in China. In the present study, two cultivated abalone species, Haliotis diversicolor supertexta and Haliotis discus hannai, were challenged with HaHV-1-CN2003 collected in 2003 in China using three different methods. Results showed that H. diversicolor supertexta was highly susceptible to HaHV-1-CN2003 infection and suffered acute mortality using all three challenge methods. H. discus hannai was not susceptible to the viral infection. Histopathology combined with transmission electron microscopy and quantitative PCR analysis revealed that the tropism of HaHV-1-CN2003 includes both neural tissue and haemocytes.

Ultrastructural analysis of Apicomplexa-Like parasites in two conch species Laevistrombus canarium and canarium urceus from Johor Straits, Malaysia

The tropical conch, Laevistrombus canarium (Linnaeus, 1758) and Canarium urceus (Linneaus, 1758) are ecologically and economically important shellfish species in Malaysia and neighboring region. Their populations, however are currently declining and this histopathological study investigates the aspect of parasitism and diseases that may affect their well-being. Conch samples were randomly collected from their natural habitat and histological sections (4-5 µm) of various organs and tissues were examined under light microscope. This was followed by ultrastructure analysis on infected tissues using transmission electron microscope (TEM). Based on the histological analysis, large numbers of gamonts, sporocysts and trophozoites of Apicomplexa-like parasites were observed in the vacuolated cells and pyramidal crypt cells of the digestive tubules, and in the digestive ducts. Furthermore, coccidian and oocysts-like Pseudoklossia sp. stages were also observed in the cells of the kidney. Apart from that, spores with cyst-like structure were observed in the digestive gland and kidney. Although the parasites were present in most of the organs analyzed, there was no obvious symptom, inflammatory response or mortality incurred on both species, which implies the possibility of a non-virulent relationship like commensalisms or mutualism. However, more investigations, including molecular studies, are needed to confirm the parasite identification and dynamics, and to further evaluate the nature of relationship between Apicomplexa parasites and their host.

Marine Infectious Disease Ecology

To put marine disease impacts in context requires a broad perspective on the roles infectious agents have in the ocean. Parasites infect most marine vertebrate and invertebrate species, and parasites and predators can have comparable biomass density, suggesting they play comparable parts as consumers in marine food webs. Although some parasites might increase with disturbance, most probably decline as food webs unravel. There are several ways to adapt epidemiological theory to the marine environment. In particular, because the ocean represents a three-dimensional moving habitat for hosts and parasites, models should open up the spatial scales at which infective stages and host larvae travel. In addition to open recruitment and dimensionality, marine parasites are subject to fishing, filter feeders, dose-dependent infection, environmental forcing, and death-based transmission. Adding such considerations to marine disease models will make it easier to predict which infectious diseases will increase or decrease in a changing ocean.

Innate resistance of New Zealand paua to abalone viral ganglioneuritis

The susceptibility of New Zealand paua (Haliotis iris) to infection by abalone herpesvirus (Haliotid herpesvirus 1; HaHV) and to the disease abalone viral ganglioneuritis (AVG) was determined. Infection challenges performed by intra-muscular injection and by immersion in infectious water containing HaHV demonstrated that New Zealand paua were highly resistant to infection by Haliotid herpesvirus 1 and were fully resistant to the disease AVG.

Viruses infecting marine molluscs

Although a wide range of viruses have been reported in marine molluscs, most of these reports rely on ultrastructural examination and few of these viruses have been fully characterized. The lack of marine mollusc cell lines restricts virus isolation capacities and subsequent characterization works. Our current knowledge is mostly restricted to viruses affecting farmed species such as oysters Crassostrea gigas, abalone Haliotis diversicolor supertexta or the scallop Chlamys farreri. Molecular approaches which are needed to identify virus affiliation have been carried out for a small number of viruses, most of them belonging to the Herpesviridae and birnaviridae families. These last years, the use of New Generation Sequencing approach has allowed increasing the number of sequenced viral genomes and has improved our capacity to investigate the diversity of viruses infecting marine molluscs. This new information has in turn allowed designing more efficient diagnostic tools. Moreover, the development of experimental infection protocols has answered some questions regarding the pathogenesis of these viruses and their interactions with their hosts. Control and management of viral diseases in molluscs mostly involve active surveillance, implementation of effective bio security measures and development of breeding programs. However factors triggering pathogen development and the life cycle and status of the viruses outside their mollusc hosts still need further investigations.

Managing marine mollusc diseases in the context of regional and international commerce: policy issues and emerging concerns

Marine mollusc production contributes to food and economic security worldwide and provides valuable ecological services, yet diseases threaten these industries and wild populations. Although the infrastructure for mollusc aquaculture health management is well characterized, its foundations are not without flaws. Use of notifiable pathogen lists can leave blind spots with regard to detection of unlisted and emerging pathogens. Increased reliance on molecular tools has come without similar attention to diagnostic validation, raising questions about assay performance, and has been accompanied by a reduced emphasis on microscopic diagnostic expertise that could weaken pathogen detection capabilities. Persistent questions concerning pathogen biology and ecology promote regulatory paralysis that impedes trade and which could weaken biosecurity by driving commerce to surreptitious channels. Solutions that might be pursued to improve shellfish aquaculture health management include the establishment of more broad-based surveillance programmes, wider training and use of general methods like histopathology to ensure alertness to emerging diseases, an increased focus on assay assessment and validation as fundamental to assay development, investment in basic research, and application of risk analyses to improve regulation. A continual sharpening of diagnostic tools and approaches and deepening of scientific knowledge is necessary to manage diseases and promote sustainable molluscan shellfish industries.

In situ hybridization and histopathological observations during ostreid herpesvirus-1-associated mortalities in Pacific oysters Crassostrea gigas

In a previous longitudinal study conducted during a mortality investigation associated with ostreid herpesvirus-1 (OsHV-1) microvariant in New Zealand Pacific oysters in 2010-2011, temporality of OsHV-1 nucleic acid detection by real-time PCR assay and onset of Pacific oyster mortality was observed. The present study further elucidated the role of OsHV-1 using an in situ hybridization (ISH) assay on sections of Pacific oysters collected from the same longitudinal study. Hybridization of the labelled probe with the target region of the OsHV-1 genome in infected cells was detected colorimetrically using nitro blue tetrazolium (NBT). OsHV-1 presence and distribution in spat indicated by the ISH signal was then compared with the existence of pathological changes in oyster tissues. Dark blue to purplish black NBT cell labelling was seen predominantly in the stroma of the mantle and gills at Day 5 post introduction to the farm. The distribution and location of ISH signals indicated the extent of OsHV-1-infected cells in multiple tissues. Histopathological abnormalities were mostly non-specific; however, a progressive pattern of increasingly widespread haemocytosis coincided with the appearance of OsHV-1-infected cells in spat collected at different time-points. The visualisation of an increasing number of OsHV-1-positive cells in spat prior to a marked increase in mortality indicated the strong likelihood of an on-going and active viral infection in some oysters. Further studies are recommended to elucidate OsHV-1 pathogenesis in Pacific oysters in association with other potentially causal variables, such as elevated temperature and interaction with Vibrio spp. bacteria.

Reprint of 'Diseases in marine invertebrates associated with mariculture and commercial fisheries'

Diseases in marine invertebrates are increasing in both frequency and intensity around the globe. Diseases in individuals which offer some commercial value are often well documented and subsequently well studied in comparison to those wild groups offering little commercial gain. This is particularly the case with those associated with mariculture or the commercial fisheries. Specifically, these include many Holothuroidea, and numerous crustacea and mollusca species. Pathogens/parasites consisting of both prokaryotes and eukaryotes from all groups have been associated with diseases from such organisms, including bacteria, viruses, fungi and protozoa. Viral pathogens in particular, appear to be an increasingly important group and research into this group will likely highlight a larger number of diseases and pathogens being described in the near future. Interestingly, although there are countless examples of the spread of disease usually associated with transportation of specific infected hosts for development of aquaculture practices, this process appears to be continuing with no real sign of effective management and mitigation strategies being implicated. Notably, even in well developed countries such as the UK and the US, even though live animal trade may be well managed, the transport of frozen food appears to be less well so and as evidence suggests, even these to have the potential to transmit pathogens when used as a food source for example.

Nutritional requirements and use of macroalgae as ingredients in abalone feed

Temperate abalone species in aquaculture have a grow‐out period of approximately 3 years because of their slow and heterogeneous growth rate. Abalone aquaculture is still a developing industry, and at least two major issues, nutrition and health, impede its development. Abalone are fed macroalgae on‐farm in a number of countries, includingChina,Korea,SouthAfrica andChile. Formulated diets are crucial to the success of abalone aquaculture in countries where abalone do not grow readily when fed brown macroalgae or when access to macroalgae is insufficient for culture. Typically, the growth rate of abalone fed formulated diets is higher than abalone fed live macroalgae. However, due to a long production period, diets for abalone not only need to sustain high growth rates, but also maintain optimal health. Feeding live macroalgae improves the feeding activity, health and marketability of abalone. In this review, the nutritional requirements of abalone and dietary ingredients used in formulated diets will be discussed, together with the use of dried macroalgal meal as a dietary ingredient in formulated diets to improve the feeding activity, health and marketability of abalone in commercial production.

Australian abalone (Haliotis laevigata, H. rubra and H. conicopora) are susceptible to infection by multiple abalone herpesvirus genotypes

From 2006 to 2012, acute mortalities occurred in farmed and wild abalone (Haliotis spp.) along the coast of Victoria, Australia. The disease (abalone viral ganglioneuritis; AVG) is associated with infection by an abalone herpesvirus (AbHV). The relative pathogenicity of 5 known variants of AbHV was evaluated on abalone stocks from different states in Australia. Results indicated that all virus variants (Vic1, Tas1, Tas2, Tas3 and Tas4) cause disease and mortality in all abalone stocks tested (greenlip, blacklip and brownlip). In order to avoid further AVG outbreaks in Australian wild abalone, strict regulations on the transfer of abalone stocks must be implemented.

EXPLORING THE CHRONIC MORTALITY AFFECTING ABALONES IN TAIWAN: DIFFERENTIATION OF ABALONE HERPESVIRUS-ASSOCIATED ACUTE INFECTION FROM CHRONIC MORTALITY BY PCR AND IN SITU HYBRIDIZATION AND HISTOPATHOLOGY

Abalone herpesvirus (AbHV) infection of cultured abalones Haliotis diversicolor supertexta induced acute high mortality in 2003. Years later, sporadic mortality was noted for an extended period of months, resulting in high cumulative mortality. Moribund abalones were analyzed using PCR, in situ hybridization, and histopathology, because thus far no viral particles have been observed by transmission electron microscopy. PCR using 20 primer sets, specifically designed from sequences of acute AbHV infection, failed to amplify any products from abalones suffering from chronic mortality. Subsequently, a 1406-bp sequence was amplified from chronic moribund abalones, and this sequence showed a 92% (553 bp/602 bp) homology with the gene of an AbHV Taiwan isolate (NCBI serial no. KF537536.1), suggestive of an AbHV pathotype. Histopathology of AbHV pathotype infection showed hemocyte infiltration in the lamina propia of the digestive tract, and hemocytes of various stages were evident, as well as the loss of seminal tubules in the gonad. In situ hybridization revealed that in AbHV infection, positive signals were restricted to the neural ganglia, while in AbHV pathotype infection, positive signals were observed only in the hemocytes. It appeared that the tropism of AbHV shifted from mainly neurotropic in AbHV infection to mainly hemocytotropic in abalone suffering from chronic mortality. Abalone shriveling syndrome-associated virus co-infection was detected in some of AbHV pathotype infection events. Further studies are needed to better understand the pathogenesis of AbHV pathotype affecting H. diversicolor in Taiwan.

Pacific oyster mortality syndrome: a marine herpesvirus active in Australia

Genotypes of Ostreid herpesvirus 1 (OsHV-1) known as microvariants cause the disease Pacific oyster mortality syndrome (POMS). Since its appearance in NSW in 2010, OsHV-1 microvariant has prevented the farming of Pacific oysters (Crassostrea gigas) in the affected estuaries near Sydney, following the initial massive outbreaks1,2. The arrival of the disease in southeast Tasmania in January 2016 has put the entire $53M industry in Australia in jeopardy3. The virus is a member of the Family Malacoherpesviridae4, which includes several invertebrate herpesviruses. The OsHV-1 genome consists of 207 439 base pairs, with organisation similar to that of mammalian herpesviruses. However, OsHV-1 contains two invertible unique regions (UL, 167.8 kbp; US, 3.4 kbp) each flanked by inverted repeats (TRL/IRL, 7.6 kbp; TRS/IRS, 9.8 kbp), with an additional unique sequence (X, 1.5 kbp) between IRL and IRS4. Unlike many herpesviruses which are host specific, OsHV-1 strains have been transmitted between marine bivalve species5 and the virus is transmitted indirectly. The virus may have relatively prolonged survival in the environment, has extremely high infection and case fatality rates, and latency is unproven. Along with pilchard herpesvirus6–8 and abalone ganglioneuritis virus9,10, it is part of a dawning reality that marine herpesviruses are among the most virulent of pathogens. Finding solutions for industry requires more than laboratory-based research.

Disease threats to wild and cultured abalone in Australia

Abalone species are important for recreational and commercial fisheries and aquaculture in many jurisdictions in Australia. Clinical infections with viral, bacterial and parasitic pathogens can cause significant losses of wild and cultured stock, and subclinical infections may result in decreased productivity and growth. Infections with abalone herpesviruses (AbHV), Vibrio spp. and parasites of the genus Perkinsus are of particular concern to Australian fisheries. Here we provide a brief overview of these three major pathogen groups and their diagnoses from an Australian perspective.

OsHV-1 countermeasures to the Pacific oyster's anti-viral response

The host-pathogen interactions between the Pacific oyster (Crassostrea gigas) and Ostreid herpesvirus type 1 (OsHV-1) are poorly characterised. Herpesviruses are a group of large, DNA viruses that are known to encode gene products that subvert their host's antiviral response. It is likely that OsHV-1 has also evolved similar strategies as its genome encodes genes with high homology to C. gigas inhibitors of apoptosis (IAPs) and an interferon-stimulated gene (termed CH25H). The first objective of this study was to simultaneously investigate the expression of C. gigas and OsHV-1 genes that share high sequence homology during an acute infection. Comparison of apoptosis-related genes revealed that components of the extrinsic apoptosis pathway (TNF) were induced in response to OsHV-1 infection, but we failed to observe evidence of apoptosis using a combination of biochemical and molecular assays. IAPs encoded by OsHV-1 were highly expressed during the acute stage of infection and may explain why we didn't observe evidence of apoptosis. However, C. gigas must have an alternative mechanism to apoptosis for clearing OsHV-1 from infected gill cells as we observed a reduction in viral DNA between 27 and 54 h post-infection. The reduction of viral DNA in C. gigas gill cells occurred after the up-regulation of interferon-stimulated genes (viperin, PKR, ADAR). In a second objective, we manipulated the host's anti-viral response by injecting C. gigas with a small dose of poly I:C at the time of OsHV-1 infection. This small dose of poly I:C was unable to induce transcription of known antiviral effectors (ISGs), but these oysters were still capable of inhibiting OsHV-1 replication. This result suggests dsRNA induces an anti-viral response that is additional to the IFN-like pathway.

Diseases in marine invertebrates associated with mariculture and commercial fisheries

Diseases in marine invertebrates are increasing in both frequency and intensity around the globe. Diseases in individuals which offer some commercial value are often well documented and subsequently well studied in comparison to those wild groups offering little commercial gain. This is particularly the case with those associated with mariculture or the commercial fisheries. Specifically, these include many Holothuroidea, and numerous crustacea and mollusca species. Pathogens/parasites consisting of both prokaryotes and eukaryotes from all groups have been associated with diseases from such organisms, including bacteria, viruses, fungi and protozoa. Viral pathogens in particular, appear to be an increasingly important group and research into this group will likely highlight a larger number of diseases and pathogens being described in the near future. Interestingly, although there are countless examples of the spread of disease usually associated with transportation of specific infected hosts for development of aquaculture practices, this process appears to be continuing with no real sign of effective management and mitigation strategies being implicated. Notably, even in well developed countries such as the UK and the US, even though live animal trade may be well managed, the transport of frozen food appears to be less well so and as evidence suggests, even these to have the potential to transmit pathogens when used as a food source for example.

The ecology, evolution, impacts and management of host-parasite interactions of marine molluscs

Molluscs are economically and ecologically important components of aquatic ecosystems. In addition to supporting valuable aquaculture and wild-harvest industries, their populations determine the structure of benthic communities, cycling of nutrients, serve as prey resources for higher trophic levels and, in some instances, stabilize shorelines and maintain water quality. This paper reviews existing knowledge of the ecology of host-parasite interactions involving marine molluscs, with a focus on gastropods and bivalves. It considers the ecological and evolutionary impacts of molluscan parasites on their hosts and vice versa, and on the communities and ecosystems in which they are a part, as well as disease management and its ecological impacts. An increasing number of case studies show that disease can have important effects on marine molluscs, their ecological interactions and ecosystem services, at spatial scales from centimeters to thousands of kilometers and timescales ranging from hours to years. In some instances the cascading indirect effects arising from parasitic infection of molluscs extend well beyond the temporal and spatial scales at which molluscs are affected by disease. In addition to the direct effects of molluscan disease, there can be large indirect impacts on marine environments resulting from strategies, such as introduction of non-native species and selective breeding for disease resistance, put in place to manage disease. Much of our understanding of impacts of molluscan diseases on the marine environment has been derived from just a handful of intensively studied marine parasite-host systems, namely gastropod-trematode, cockle-trematode, and oyster-protistan interactions. Understanding molluscan host-parasite dynamics is of growing importance because: (1) expanding aquaculture; (2) current and future climate change; (3) movement of non-native species; and (4) coastal development are modifying molluscan disease dynamics, ultimately leading to complex relationships between diseases and cultivated and natural molluscan populations. Further, in some instances the enhancement or restoration of valued ecosystem services may be contingent on management of molluscan disease. The application of newly emerging molecular tools and remote sensing techniques to the study of molluscan disease will be important in identifying how changes at varying spatial and temporal scales with global change are modifying host-parasite systems.

Using the Neptune project to benefit Australian aquatic animal health research

Diseases of aquatic animals have had, and continue to have, a significant impact on aquatic animal health. In Australia, where fisheries and aquaculture are important industries, aquatic species have been subject to serious disease outbreaks, including pilchard herpesvirus, the cause of one of the largest wild fish kills ever recorded. At the same time, there is a consensus that Australia's parasite fauna are largely unknown, and that aquatic animal health information is difficult to access. Managing aquatic animal diseases is challenging because they may be entirely new, their hosts may be new to aquaculture, and specialist expertise and basic diagnostic tools may be lacking or absent. The Neptune project was created in response to these challenges, and it aims to increase awareness of aquatic animal diseases, improve disease management, and promote communication between aquatic animal health professionals in Australia. The project consists of an online database, a digital microscopy platform containing a whole-slide image library, a community space, and online communications technology. The database contains aquatic animal health information from published papers, government reports, and other sources, while the library contains slides of key diseases both endemic and exotic to Australia. These assets make Neptune a powerful resource for researchers, students, and biosecurity officials.

Infectious diseases affect marine fisheries and aquaculture economics

Seafood is a growing part of the economy, but its economic value is diminished by marine diseases. Infectious diseases are common in the ocean, and here we tabulate 67 examples that can reduce commercial species' growth and survivorship or decrease seafood quality. These impacts seem most problematic in the stressful and crowded conditions of aquaculture, which increasingly dominates seafood production as wild fishery production plateaus. For instance, marine diseases of farmed oysters, shrimp, abalone, and various fishes, particularly Atlantic salmon, cost billions of dollars each year. In comparison, it is often difficult to accurately estimate disease impacts on wild populations, especially those of pelagic and subtidal species. Farmed species often receive infectious diseases from wild species and can, in turn, export infectious agents to wild species. However, the impact of disease export on wild fisheries is controversial because there are few quantitative data demonstrating that wild species near farms suffer more from infectious diseases than those in other areas. The movement of exotic infectious agents to new areas continues to be the greatest concern.

Anti-viral gene induction is absent upon secondary challenge with double-stranded RNA in the Pacific oyster, Crassostrea gigas

Oyster farming is one of the most important aquaculture industries in the world. However, its productivity is increasingly limited by viral disease and we do not yet have management practices, such as protective vaccination, that can control these disease outbreaks. Hence, in the current study we investigated the expression of known anti-viral genes in oysters (Crassostrea gigas) in response to primary and secondary encounter with a virus associated molecular pattern (dsRNA), and tested whether a common form of epigenetic gene regulation (DNA methylation) was associated with the expression of these anti-viral genes. Injection of dsRNA into the adductor muscle resulted in the rapid and transient expression of virus recognition receptors (TLR & MDA5), whereas several anti-viral signalling (IRF & SOC-1) and effector (PKR & viperin) genes were still up-regulated at one week post primary challenge (p < 0.05). This primary encounter with dsRNA appeared to deplete the immune system because anti-viral gene induction was absent in the gills when oysters were given a second injection of dsRNA at 1-week post-primary injection. The expression of DNA methylation genes (DNMT1, DNMT3b, TDG, TET2) and DNA methylation profiles up-stream of specific anti-viral genes (STING, SOC-1 & Viperin) did not change in response to dsRNA injection (p > 0.05). These results collectively suggest that C. gigas does not have an enhanced anti-viral gene response (immune-priming) to secondary dsRNA challenge and that the sustained up-regulation of anti-viral signalling and effector genes following primary challenge is unlikely to be associated with upstream DNA methylation levels.

Abalone farm discharges the withering syndrome pathogen into the wild

An intracellular bacterium Candidatus Xenohaliotis californiensis, also called Withering-Syndrome Rickettsia-Like Organism (WS-RLO), is the cause of mass mortalities that are the chief reason for endangerment of black abalone (Haliotis cracherodii). Using a real-time PCR assay, we found that a shore-based abalone farm (AF) in Santa Barbara, CA, USA discharged WS-RLO DNA into the ocean. Several other shore-based AFs discharge effluent into critical habitat for black abalone in California and this might affect the recovery of wild black abalone. Existing regulatory frameworks exist that could help protect wild species from pathogens released from shore-based aquaculture.

The development of a loop-mediated isothermal amplification assay for rapid and sensitive detection of abalone herpesvirus DNA

A loop-mediated isothermal amplification (LAMP) assay was developed for the detection of abalone herpesvirus DNA. Two pairs of primers were designed, based on the sequence of the DNA polymerase gene of abalone herpesvirus. The reaction temperature and time were optimized to 63°C and 60min, respectively. LAMP amplicons were analyzed by 2% agarose gel electrophoresis or by visual inspection of a colour change emitted by fluorescent dye. The method developed was specific for the detection of abalone herpesvirus, without cross-reactions with other tested herpesviruses including ostreid herpesvirus 1 (OsHV-1), European eel herpesvirus, koi herpesvirus (KHV) and an avian herpesvirus. The LAMP assay was 100 folds more sensitive than a conventional PCR and 10 folds less sensitive than a SYBR Green PCR. These results indicate that the developed LAMP assay is a simple, rapid, sensitive, specific and reliable technique for the detection of abalone herpesvirus.

Physiological change under OsHV-1 contamination in Pacific oyster Crassostrea gigas through massive mortality events on fields

BACKGROUND

Massive mortalities have been observed in France since 2008 on spat and juvenile Pacific oysters, Crassostrea gigas. A herpes virus called OsHV-1, easily detectable by PCR, has been implicated in the mortalities as demonstrated by the results of numerous field studies linking mortality with OsHV-1 prevalence. Moreover, experimental infections using viral particles have documented the pathogenicity of OsHV-1 but the physiological responses of host to pathogen are not well known.

RESULTS

The aim of this study was to understand mechanisms brought into play against the virus during infection in the field. A microarray assay has been developed for a major part of the oyster genome and used for studying the host transcriptome across mortality on field. Spat with and without detectable OsHV-1 infection presenting or not mortality respectively were compared by microarray during mortality episodes. In this study, a number of genes are regulated in the response to pathogen infection on field and seems to argue to an implication of the virus in the observed mortality. The result allowed establishment of a hypothetic scheme of the host cell's infection by, and response to, the pathogen.

CONCLUSIONS

This response shows a "sensu stricto" innate immunity through genic regulation of the virus OsHV-1 life cycle, but also others biological processes resulting to complex interactions between host and pathogens in general.

Complete genome sequence of acute viral necrosis virus associated with massive mortality outbreaks in the Chinese scallop, Chlamys farreri

BACKGROUND

Acute viral necrosis virus (AVNV) is the causative agent of a serious disease resulting in high mortality in cultured Chinese scallops, Chlamys farreri. We have sequenced and analyzed the complete genome of AVNV.

RESULTS

The AVNV genome is a linear, double-stranded DNA molecule of 210,993 bp with a nucleotide composition of 38.5% G + C. A total of 123 open reading frames were predicted to encode functional proteins, ranging from 41 to 1,878 amino acid residues. The DNA sequence of AVNV is 97% identical to that of ostreid herpesvirus 1 (OsHV-1), and the amino acid sequences of the encoded proteins of these two viruses are 94-100% identical. The genomic organization of AVNV is similar to that of OsHV-1, and consists of two unique regions (170.4 kb and 3.4 kb, respectively), each flanked by two inverted repeats (7.6 kb and 10.2 kb, respectively), with a third unique region (1.5 kb) situated between the two internal repeats.

CONCLUSIONS

Our results indicate that AVNV is a variant of OsHV-1. The AVNV genome sequence provides information useful for understanding the evolution and divergence of OsHV-1 in marine molluscs.

cDNA microarray analysis of disk abalone genes in gills and hemocytes after viral hemorrhagic septicemia virus (VHSV) challenge

A disk abalone Haliotis discus discus 4.2 K cDNA microarray was designed by selecting abalone expressed sequence tags (ESTs). Transcriptional profiles in gills and hemocytes were analyzed upon abalone challenged with viral hemorrhagic septicemia virus (VHSV) in order to select candidates for screening of immune response genes. Among the 4188 genes analyzed, 280 (6.6%) transcripts were changed their expression level in gills and hemocytes against VHSV challenge compared to control animals. Total of 88 and 65 genes were up-regulated in gills and hemocytes, respectively. These genes can be grouped under various immune-functional categories such as transcription factors (Krüppell-like factor; ETS-family transcription factor), inflammatory and apoptosis related genes (TNF superfamily members, Fas ligand), IFN regulatory proteins (IFN-44 like, interferon gamma-inducible lysosomal thiol reductase) and detoxification proteins (glutathione peroxidase). In contrast, 25 and 102 genes were shown down-regulation in gills and hemocytes, respectively. Among the differentially expressed transcripts, considerably higher numbers of ESTs were represented as either hypothetical (unknown) proteins or no GenBank match suggesting those may be novel genes associated with internal defense of abalone.

Development of a polymerase chain reaction for the detection of abalone herpesvirus infection based on the DNA polymerase gene

A 5781-base pair (bp) fragment of genomic DNA from the Taiwanese abalone herpesvirus was obtained and showed 99% (5767/5779) homology in the nucleotide sequence and 99% (1923/1926) in the amino acid sequence with the DNA polymerase gene of the abalone herpesvirus strain Victoria/AUS/2007. Homology of the amino acid sequence with the DNA polymerase of ostreid herpesvirus 1 was 30% (563/1856). In this study, a PCR-based procedure for detecting herpesvirus infection of abalone, Haliotis diversicolor supertexta, in Taiwan was developed. The method employed primer sets targeting the viral DNA polymerase gene, and was able to amplify DNA fragments of the expected size from infected samples. Primer sets of 40f and 146r were designed for amplification of an expected PCR product of 606 bp. Combining the new PCR protocol with histopathology, this assay can serve as a reliable diagnostic for herpesvirus infections in abalone.

Influence of elevated temperatures on the immune response of abalone, Haliotis rubra

Elevated water temperature can act as a stressor impacting the immune responses of molluscs, potentially increasing their susceptibility to microbial infections. Abalone are commercially important marine molluscs that have recently experienced disease outbreaks caused by a herpesvirus and Vibrio bacteria. Sampling of wild-caught Haliotis rubra showed a significant correlation between water temperature and both antiviral and antibacterial activity, with higher activity in summer than in winter months. However, antibacterial activity was compromised in favour of antiviral activity as the water temperatures peaked in summer. A controlled laboratory experiment was then used to investigate several immune responses of H. rubra, including total haemocyte count (THC), stimulated superoxide anion production (SO), antiviral activity against a model herpesvirus, herpes simplex virus type 1 and antibacterial activity against a representative pathogenic bacterium, Vibrio anguillarum, over one week after raising water temperature from 18 to 21 or 24 °C. THC and SO increased at day 1 and then dropped back to control levels by days 3 and 7. By comparison, the humoural immune parameters showed a delayed response with antibacterial and antiviral activity significantly increasing on days 3 and 7, respectively. Consistent with the field study, antibacterial activity became significantly depressed after prolonged exposure to elevated temperatures. A principal components analysis on the combined immune parameters showed a negative correlation between antiviral and antibacterial activity. SO was positively correlated to THC and neither of these cellular parameters were correlated to the humoural antimicrobial activity. Overall, this study indicates that abalone may have more resilience to viruses than bacterial pathogens under conditions of elevated temperature, such as those predicted under future climate change scenarios.

Abalone viral ganglioneuritis: establishment and use of an experimental immersion challenge system for the study of abalone herpes virus infections in Australian abalone

In late 2005, acute mortalities occurred in abalone on farms located in Victoria, Australia. Disease was associated with infection by an abalone herpes virus (AbHV). Subsequently, starting in 2006, the disease (abalone viral ganglioneuritis; AVG) was discovered in wild abalone in Victorian open waters. Currently, it continues to spread, albeit at a slow rate, along the Victorian coast-line. Here, we report on experimental transmission trials that were carried out by immersion using water into which diseased abalone had shed infectious viral particles. At various time points following exposure, naïve abalone were assessed by an AbHV-specific real-time PCR and histological analyses including in situ hybridization (ISH). Results demonstrated that while exposed abalone began displaying clinical signs of the disease from 60 hours post exposure (hpe), they tested positive for the presence of viral DNA at 36 hpe. Of further interest, the AbHV DNA probe used in the ISH assay detected the virus as early as 48 hpe.

Survey estimates of fishable biomass following a mass mortality in an Australian molluscan fishery

Mass mortality events are relatively uncommon in commercially fished populations, but when they occur, they reduce production and degrade ecosystems. Observing and documenting mass mortalities is simpler than quantifying the impact on stocks, monitoring or predicting recovery, and re-establishing commercial fishing. Direct survey measures of abundance, distribution and harvestable biomass provide the most tenable approach to informing decisions about future harvests in cases where stock collapses have occurred because conventional methods have been disrupted and are less applicable. Abalone viral ganglioneuritis (AVG) has resulted in high levels of mortality across all length classes of blacklip abalone, Haliotis rubra Leach, off western Victoria, Australia, since May 2006. Commercial catches in this previously valuable fishery were reduced substantially. This paper describes the integration of research surveys with commercial fishermen's knowledge to estimate the biomass of abalone on AVG-impacted reefs. Experienced commercial abalone divers provided credible information on the precise locations of historical fishing grounds within which fishery-independent surveys were undertaken. Abalone density estimates remained low relative to pre-AVG levels, and total biomass estimates were similar to historical annual catch levels, indicating that the abalone populations have yet to adequately recover. Survey biomass estimates were incorporated into harvest decision tables and used with prior accumulated knowledge of the populations to determine a conservative harvest strategy for the fishery.