Antibody profiling using a recombinant protein–based multiplex ELISA array accelerates recombinant vaccine development: Case study on red sea bream iridovirus as a reverse vaccinology model

Megalocytivirus and Other Members of the Family Iridoviridae in Finfish: A Review of the Etiology, Epidemiology, Diagnosis, Prevention and Control

Aquaculture has expanded to become the fastest growing food-producing sector in the world. However, its expansion has come under threat due to an increase in diseases caused by pathogens such as iridoviruses commonly found in aquatic environments used for fish farming. Of the seven members belonging to the family Iridoviridae, the three genera causing diseases in fish comprise ranaviruses, lymphocystiviruses and megalocytiviruses. These three genera are serious impediments to the expansion of global aquaculture because of their tropism for a wide range of farmed-fish species in which they cause high mortality. As economic losses caused by these iridoviruses in aquaculture continue to rise, the urgent need for effective control strategies increases. As a consequence, these viruses have attracted a lot of research interest in recent years. The functional role of some of the genes that form the structure of iridoviruses has not been elucidated. There is a lack of information on the predisposing factors leading to iridovirus infections in fish, an absence of information on the risk factors leading to disease outbreaks, and a lack of data on the chemical and physical properties of iridoviruses needed for the implementation of biosecurity control measures. Thus, the synopsis put forth herein provides an update of knowledge gathered from studies carried out so far aimed at addressing the aforesaid informational gaps. In summary, this review provides an update on the etiology of different iridoviruses infecting finfish and epidemiological factors leading to the occurrence of disease outbreaks. In addition, the review provides an update on the cell lines developed for virus isolation and culture, the diagnostic tools used for virus detection and characterization, the current advances in vaccine development and the use of biosecurity in the control of iridoviruses in aquaculture. Overall, we envision that the information put forth in this review will contribute to developing effective control strategies against iridovirus infections in aquaculture.

Complete genome sequences of infectious spleen and kidney necrosis virus isolated from farmed albino rainbow sharks Epalzeorhynchos frenatum in the United States

The genus Megalocytivirus includes viruses known to cause significant disease in aquacultured fish stocks. Herein, we report the complete genome sequences of two megalocytiviruses (MCVs) isolated from diseased albino rainbow sharks Epalzeorhynchos frenatum reared on farms in the United States in 2018 and 2019. Histopathological examination revealed typical megalocytivirus microscopic lesions (i.e., basophilic cytoplasmic inclusions) that were most commonly observed in the spleen and kidney. Transmission electron microscopic examination of spleen and kidney tissues from specimens of the 2018 case revealed hexagonally shaped virus particles with a mean diameter of 153 ± 6 nm (n = 20) from opposite vertices and 131 ± 5 nm (n = 20) from opposite faces. Two MCV-specific conventional PCR assays confirmed the presence of MCV DNA in the collected samples. Full genome sequencing of both 2018 and 2019 Epalzeorhynchos frenatus iridoviruses (EFIV) was accomplished using a next-generation sequencing approach. Phylogenomic analyses revealed that both EFIV isolates belong to the infectious spleen and kidney necrosis virus (ISKNV) genotype within the genus Megalocytivirus. This study is the first report of ISKNV in albino rainbow sharks.

Isolation and characterisation of an ISKNV-genotype megalocytivirus from imported angelfish Pterophyllum scalare

Using cultures of the SKF-9 cell line, megalocytivirus AFIV-16 was isolated from imported angelfish Pterophyllum scalare held in quarantine at the Australian border. The cytopathic effect caused by isolate AFIV-16 presented as cell rounding and enlargement, but complete destruction of the infected cell cultures did not occur. The infected cells demonstrated immunocytochemical reactivity with monoclonal antibody M10, which is used for diagnosis of OIE-listed red sea bream iridoviral disease. Using electron microscopy, the virus particles, consisting of hexagonal nucleocapsids, were observed in the cytoplasm of SKF-9 cells. The replication of AFIV-16 in cultured SKF-9 cells was significantly greater at 28°C incubation than at 22 and 25°C incubation, whereas no difference in growth characteristics was observed for red sea bream iridovirus (RSIV) isolate KagYT-96 across this temperature range. Whole genome sequencing demonstrated that AFIV-16 has a 99.96% similarity to infectious spleen and kidney necrosis virus (ISKNV), the type species in the genus Megalocytivirus. AFIV-16 was classified into ISKNV genotype Clade 1 by phylogenetic analysis of the major capsid protein gene nucleotide sequence. This is the first report of whole genome sequencing of an ISKNV genotype megalocytivirus isolated from ornamental fish.

Carbon nanotube-based DNA vaccine against koi herpesvirus given by intramuscular injection

Koi herpesvirus (KHV) also named Cyprinid Herpesvirus 3 (CyHV-3) is one of the most threatening pathogens affecting common carp production as well as the valued ornamental koi carp. The current commercial vaccines available are costly and potentially cause severe stress caused by live virus. KHV ORF149 gene has been proved encoding one of the main immunogenic proteins for KHV. In this study, we coupled a plasmid expression vector for ORF149 to single walled carbon nanotubes (SWCNTs) for an anti-KHV vaccine. The vaccine conferred an 81.9% protection against intraperitoneal challenge with KHV. Importantly, SWCNTs as a promising vehicle can enhanced the protective effects 33.9% over that of the naked DNA vaccine at the same dose. The protection was longer and serum antibody production, enzyme activities and immune-related gene expression were all induced in fish vaccinated with the nanotube-DNA vaccine compared with the DNA alone. Thereby, this study demonstrates that the ORF149 DNA vaccine loaded onto SWCNTs as a novel vaccine might provide an effective method of coping with KHV disease using intra-muscular vaccination.