Development of an attenuated vaccine against Koi Herpesvirus Disease (KHVD) suitable for oral administration and immersion

Fish Iridoviridae: infection, vaccination and immune response

Each year, due to climate change, an increasing number of new pathogens are being discovered and studied, leading to an increase in the number of known diseases affecting various fish species in different regions of the world. Viruses from the family Iridoviridae, which consist of the genera Megalocytivirus, Lymphocystivirus, and Ranavirus, cause epizootic outbreaks in farmed and wild, marine, and freshwater fish species (including ornamental fish). Diseases caused by fish viruses of the family Iridoviridae have a significant economic impact, especially in the aquaculture sector. Consequently, vaccines have been developed in recent decades, and their administration methods have improved. To date, various types of vaccines are available to control and prevent Iridoviridae infections in fish populations. Notably, two vaccines, specifically targeting Red Sea bream iridoviral disease and iridoviruses (formalin-killed vaccine and AQUAVAC® IridoV, respectively), are commercially available. In addition to exploring these themes, this review examines the immune responses in fish following viral infections or vaccination procedures. In general, the evasion mechanisms observed in iridovirus infections are characterised by a systemic absence of inflammatory responses and a reduction in the expression of genes associated with the adaptive immune response. Finally, this review also explores prophylactic procedure trends in fish vaccination strategies, focusing on future advances in the field.

Genomic and molecular characterization of a cyprinid herpesvirus 2 YC-01 strain isolated from gibel carp

Cyprinid herpesvirus 2 (CyHV-2) is the pathogen of herpesviral hematopoietic necrosis (HVHN), causing the severe economic losses in farmed gibel carp (Carassius gibelio). Further exploration of the genome structure and potential molecular pathogenesis of CyHV-2 through complete genome sequencing, comparative genomics, and molecular characterization is required. Herein, the genome of a CyHV-2 YC-01 strain isolated from diseased gibel carp collected in Yancheng, Jiangsu Province, China was sequenced, then we analyzed the genomic structure, genetic properties, and molecular characterization. First, the complete YC-01 genome comprises 275,367 bp without terminal repeat (TR) regions, with 151 potential open reading frames (ORFs). Second, compared with other representative published strains of the genus Cyvirus, several evident variations are found in YC-01, particularly the orientation and position of ORF25 and ORF25B. ORF107 and ORF156 are considered as potential molecular genetic markers for YC-01. ORF55 (encoding thymidine kinase) might be used to distinguish YC-01 and ST-J1 from other CyHV-2 isolates. Third, phylogenetically, YC-01 clusters with the members of the genus Cyvirus (together with the other six CyHV-2 isolates). Fourth, 43 putative proteins are predicted to be functional and are mainly divided into five categories. Several conserved motifs are found in nucleotide, amino acid, and promoter sequences including cis-acting elements identification of YC-01. Finally, the potential virulence factors and linear B cell epitopes of CyHV-2 are predicted to supply possibilities for designing novel vaccines rationally. Our results provide insights for further understanding genomic structure, genetic evolution, and potential molecular mechanisms of CyHV-2.

Generation and Characterization of ORF55/ORF57-Deleted Recombinant Cyprinid herpesvirus 2 Mutants with Chimeric Capsid Protein Gene of Grouper Nervous Necrosis Virus

Cyprinid herpesvirus 2 (CyHV-2) is a pathogen that causes significant losses to the global aquaculture industry due to mass mortality in crucian carp and goldfish. This study demonstrates that the ORF55/ORF57 deletion mutants CyHV-2-Δ55-CP and CyHV-2-Δ57-CP obtained through homologous recombination replicate effectively within the caudal fin of Carassius auratus gibelio (GiCF) cells and exhibit morphologies similar to the CyHV-2 wild-type strain. Both mutants demonstrated a decrease in virulence, with CyHV-2-Δ57-CP exhibiting a more significant reduction. This serves as a reference for the subsequent development of recombinant attenuated vaccines against CyHV-2. Additionally, both mutants expressed the inserted RGNNV-CP (capsid protein of Redspotted grouper nervous necrosis virus) fusion protein gene, and inoculation with CyHV-2-Δ57-CP-infected GiCF cell lysates elicited an antibody response in the grouper. These results indicate that, while ORF55 and ORF57 genes of CyHV-2 are not required for viral replication in vitro, they do play a role in virulence in vivo. Additionally, expression of foreign protein in CyHV-2 suggests that the fully attenuated mutant of CyHV-2 could potentially function as a viral vector for developing subunit vaccines or multivalent recombinant attenuated vaccines.

Oral vaccination with novel Lactococcus lactis mucosal live vector-secreting Brucella lumazine synthase (BLS) protein induces humoral and cellular immune protection against Brucella abortus

This work aimed to provide recombinant Lactococcus lactis as a potential live vector for the manufacture of recombinant Brucella abortus (rBLS-Usp45). The sequences of the genes were collected from the GenBank database. Using Vaxijen and ccSOL, the proteins' immunogenicity and solubility were evaluated. Mice were given oral vaccinations with recombinant L. lactis. Anti-BLS-specific IgG antibodies were measured by ELISA assay. Cytokine reactions were examined using real-time PCR and the ELISA technique. The BLS protein was chosen for immunogenicity based on the vaccinology screening findings since it had maximum solubility and antigenic values ​​of 99% and 0.75, respectively. The BLS gene, digested at 477 bp, was electrophoretically isolated to demonstrate that the recombinant plasmid was successfully produced. Protein-level antigen expression showed that the target group produced the 18 kDa-sized BLS protein, whereas the control group did not express any proteins. In the sera of mice given the L. lactis-pNZ8148-BLS-Usp45 vaccine 14 days after priming, there was a significant level of BLS-specific IgG1, IgG2a (P < 0.001) compared to the PBS control group. Vaccinated mice showed higher levels of IFN-γ, TNFα, IL-4, and IL-10 in samples obtained on days 14 and 28, after receiving the L. lactis-pNZ8148-BLS-Usp45 and IRBA vaccines (P < 0.001). The inflammatory reaction caused less severe spleen injuries, alveolar edema, lymphocyte infiltration, and morphological damage in the target group's spleen sections. Based on our findings, an oral or subunit-based vaccine against brucellosis might be developed using L. lactis-pNZ8148-BLS-Usp45 as a novel, promising, and safe alternative to the live attenuated vaccines now available.

Protective effects of immersion immunization of koi with Escherichia coli DH5α carrying DNA vaccine against koi herpesvirus

This study aims to immunize the koi fingerlings immersion using the formalin-killed and freeze-dried E. coli DH5α carrying plasmid for the KHV DNA vaccine. 200 fish on each tank in a total water volume of 20 L. Each tanks consists of different vaccination group: PBS as control (10 mL; C), empty E. coli DHα (10 mL at 108 CFU mL-1; E), formalinkilled E. coli DHα:ORF81 (10 mL at 108 CFU mL-1; KE), freezedried E.coli DHα:ORF81 without formalin inactivation (10 mL at 108 CFU mL-1; FE), and formalin-killed and then freeze-dried E. coli DHα:ORF81 (10 mL at 108 CFU mL-1; KFE). The bath vaccination was conducted for 1 × 30 min. For the challenged test, fish were immersed with the 100 mL of LD50 dose of KHV (10-2 dilution from the KHV stock) for 30 min. The vaccination using E. coli DH5α:ORF81 could significantly modulate the innate and adaptive immunity of the fish and result in higher fish survival after KHV infection. The vaccination using formalin-killed or formalin-killed and freezedried E. coli DH5α:ORF81 will be further developed as an alternative to the costefficient koi or carp fingerlings vaccination method.

Current status and development prospects of aquatic vaccines

Diseases are a significant impediment to aquaculture's sustainable and healthy growth. The aquaculture industry is suffering significant financial losses as a result of the worsening water quality and increasing frequency of aquatic disease outbreaks caused by the expansion of aquaculture. Drug control, immunoprophylaxis, ecologically integrated control, etc. are the principal control strategies for fish infections. For a long time, the prevention and control of aquatic diseases have mainly relied on the use of various antibiotics and chemical drugs. However, long-term use of chemical inputs not only increases pathogenic bacteria resistance but also damages the fish and aquaculture environments, resulting in drug residues in aquatic products, severely impeding the development of the aquaculture industry. The development and use of aquatic vaccines are the safest and most effective ways to prevent aquatic animal diseases and preserve the health and sustainability of aquaculture. To give references for the development and implementation of aquatic vaccines, this study reviews the development history, types, inoculation techniques, mechanisms of action, development prospects, and challenges encountered with aquatic vaccines.