Fish immunization has been carried out for over 50 years and is generally accepted as an effective method for preventing a wide range of bacterial and viral diseases. Vaccination efforts contribute to environmental, social, and economic sustainability in global aquaculture. Most licensed fish vaccines have traditionally been inactivated microorganisms that were formulated with adjuvants and delivered through immersion or injection routes. Live vaccines are more efficacious, as they mimic natural pathogen infection and generate a strong antibody response, thus having a greater potential to be administered via oral or immersion routes. Modern vaccine technology has targeted specific pathogen components, and vaccines developed using such approaches may include subunit, or recombinant, DNA/RNA particle vaccines. These advanced technologies have been developed globally and appear to induce greater levels of immunity than traditional fish vaccines. Advanced technologies have shown great promise for the future of aquaculture vaccines and will provide health benefits and enhanced economic potential for producers. This review describes the use of conventional aquaculture vaccines and provides an overview of current molecular approaches and strategies that are promising for new aquaculture vaccine development.

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BackgroundVerticillium dahliae is a soil-borne fungus that causes vascular wilt diseases in a wide range of plant hosts. V. dahliae produces multicelled, melanized resting bodies, also known as microsclerotia (MS) that can survive for years in the soil. The MS are the primary source of infection of the Verticillium disease cycle. Thus, MS formation marks an important event in the disease cycle of V. dahliae.ResultsIn this study, next generation sequencing technology of RNA-Seq was employed to investigate the global transcriptomic dynamics of MS development to identify differential gene expression at several stages of MS formation in strain XS11 of V. dahliae, isolated from smoke tree. We observed large-scale changes in gene expression during MS formation, such as increased expression of genes involved in protein metabolism and carbohydrate metabolism. Genes involved in glycolytic pathway and melanin biosynthesis were dramatically up-regulated in MS. Cluster analyses revealed increased expression of genes encoding products involved in primary metabolism and stress responses throughout MS development. Differential expression of ubiquitin-dependent protein catabolism and cell death-associated genes during MS development were revealed. Homologs of genes located in the lineage-specific (LS) regions of V. dahliae strain VdLs.17, were either not expressed or showed low expression. Furthermore, alternative splicing (AS) events were analyzed, revealing that over 95.0% AS events involve retention of introns (RI).ConclusionsThese data reveal the dynamics of transcriptional regulation during MS formation and were used to construct a comprehensive high-resolution gene expression map. This map provides a key resource for understanding the biology and molecular basis of MS development of V. dahliae.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-324) contains supplementary material, which is available to authorized users.

Tilapia is one of the most important economic and fastest-growing species in aquaculture worldwide. In 2015, an epidemic associated with severe mortality occurred in adult tilapia in Hubei, China. The causative pathogen was identified as Tilapia parvovirus (TiPV) by virus isolation, electron microscopy, experimental challenge, In situ hybridization (ISH), indirect immunofluorescence (IFA), and viral gene sequencing. Electron microscopy revealed large numbers of parvovirus particles in the organs of diseased fish, including kidney, spleen, liver, heart, brain, gill, intestine, etc. The virions were spherical in shape, non-enveloped and approximately 30nm in diameter. The TiPV was isolated and propagated in tilapia brain cells (TiB) and induced a typical cytopathic effect (CPE) after 3 days post-infection (dpi). This virus was used to experimentally infect adult tilapia and clinical disease symptoms similar to those observed naturally were replicated. Additionally, the results of ISH and IFA showed positive signals in kidney and spleen tissues from TiPV-infected fish. To identify TiPV-specific sequences, the near complete genome of TiPV was obtained and determined to be 4269 bp in size. Phylogenetic analysis of the NS1 sequence revealed that TiPV is a novel parvovirus, forms a separate branch in proposed genus Chapparvovirus of Parvoviridae . Results presented here confirm that TiPV is a novel parvovirus pathogen that can cause massive mortality in adult tilapia. This provides a basis for the further studies to define the epidemiology, pathology, diagnosis, prevention and treatment of this emerging viral disease.

A novel fish reovirus, Hubei grass carp disease reovirus (HGDRV; formerly grass carp reovirus strain 104, GCRV104), was isolated from diseased grass carp in China in 2009 and the full genome sequence was determined. This reovirus was propagated in a grass carp kidney cell line with a typical cytopathic effect. The total size of the genome was 23 706 bp with a 51 mol% G+C content, and the 11 dsRNA segments encoded 12 proteins (two proteins encoded by segment 11). A nucleotide sequence similarity search using BLASTN found no significant matches except for segment 2, which partially matched that of the RNA-dependent RNA polymerase (RdRp) from several viruses in the genera Aquareovirus and Orthoreovirus of the family Reoviridae. At the amino acid level, seven segments (Seg-1 to Seg-6, and Seg-8) matched with species in the genera Aquareovirus (15-46 % identities) and Orthoreovirus (12-44 % identities), while for four segments (Seg-7, Seg-9, Seg-10 and Seg-11) no similarities in these genera were found. Conserved terminal sequences, 59-GAAUU--UCAUC-39, were found in each HGDRV segment at the 59 and 39 ends, and the 59-terminal nucleotides were different from any known species in the genus Aquareovirus. Phylogenetic analysis based on RdRp amino acid sequences from members of the family Reoviridae showed that HGDRV clustered with aquareoviruses prior to joining a branch common with orthoreoviruses. Based on these observations, we propose that HGDRV is a new species in the genus Aquareovirus that is distantly related to any known species within this genus.

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The development of a safe and efficient dengue vaccine represents a global challenge in public health. Chimeric dengue viruses (DENV) based on an attenuated flavivirus have been well developed as vaccine candidates by using reverse genetics. In this study, based on the full-length infectious cDNA clone of the well-known Japanese encephalitis virus live vaccine strain SA14-14-2 as a backbone, a novel chimeric dengue virus (named ChinDENV) was rationally designed and constructed by replacement with the premembrane and envelope genes of dengue 2 virus. The recovered chimeric virus showed growth and plaque properties similar to those of the parental DENV in mammalian and mosquito cells. ChinDENV was highly attenuated in mice, and no viremia was induced in rhesus monkeys upon subcutaneous inoculation. ChinDENV retained its genetic stability and attenuation phenotype after serial 15 passages in cultured cells. A single immunization with various doses of ChinDENV elicited strong neutralizing antibodies in a dose-dependent manner. When vaccinated monkeys were challenged with wild-type DENV, all animals except one that received the lower dose were protected against the development of viremia. Furthermore, immunization with Chin-DENV conferred efficient cross protection against lethal JEV challenge in mice in association with robust cellular immunity induced by the replicating nonstructural proteins. Taken together, the results of this preclinical study well demonstrate the great potential of ChinDENV for further development as a dengue vaccine candidate, and this kind of chimeric flavivirus based on JE vaccine virus represents a powerful tool to deliver foreign antigens.

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