Genome Characterization and Phylogenetic Analysis of Scale Drop Disease Virus Isolated from Asian Seabass (Lates calcarifer).

Scale drop disease virus (SDDV), a double-stranded DNA virus in the family Iridoviridae, has been reported widely in southeast Asian countries as a causative agent of scale drop syndrome (SDS) in Asian seabass. SDS has resulted in high mortality and significant economic losses to the aquaculture industry. This study demonstrated the use of metagenomic methods to investigate bacterial and viral communities present in infected fish tissues and recover a complete genome of the causative agent named SDDV TH7_2019. Characterization of the TH7_2019 genome revealed a genome size of 131 kb with 134 putative ORFs encoding viral proteins potentially associated with host apoptosis manipulation. A comparative genome analysis showed a high degree of amino acid identity across SDDV strains, with variations in number of repeat sequences and mutations within core genes. Phylogenetic analyses indicate a close relationship among SDDV genomes. This research enhances our understanding of the genetic diversity and evolutionary relationship of SDDV, contributing valuable insights for further development of effective control strategies of SDDV.

Factors Influencing Disease Dynamics in Small-Scale Carp Polyculture in Bangladesh.

Small-scale carp polyculture plays a key role in food supply in Bangladesh. However, factors including water pollution, limited infrastructure, and inadequate disease management hinder its sustainability. This paper reports on a survey of 231 farmers across the six major carp producing regions in Bangladesh, analyzing factors including farmers' social aspects, farm characteristics, information on disease and approaches adopted to combat them, and biosecurity practices. Almost half (46.8%) of the farms surveyed experienced disease in carp species, with clear regional variations. Eighty-four percent of farms reported carp mortalities during disease outbreaks, with an average mortality level of 10.23 ± 11.81%. Clinical signs during outbreaks lasted between a week and a month, with a peak in disease outbreaks occurring in two seasonal periods between June and July and October and December. Disease incidence was related to a range of factors including the farmer's experience, ponds/farm type, stocked species, and biosecurity practice. A combination of disinfecting measures during pond preparation and measures during stocking, including discarding fingerling transport water away from the farm, fingerling disinfection, and checking the health of fingerlings before stocking, significantly reduced disease occurrence. Treatments involving antibiotics, ciprofloxacin, erythromycin, and azithromycin were reported as ineffective, raising concerns about their non-prudent use, inadequate dosing (perhaps without appropriate veterinary guidance), and the potential for driving antimicrobial resistance in the environment. The research unveils a concerning pattern of high disease incidence across small-scale carp farms in Bangladesh, and the significant potential for disease spread highlights the need for responsible disposal practices. The study emphasizes the need for improving training and awareness programs for addressing biosecurity and disease management challenges, ensuring sustainable aquaculture and community well-being.

Development of a bivalent mucoadhesive nanovaccine to prevent francisellosis and columnaris diseases in Nile tilapia (Oreochromis niloticus).

The occurrence of francisellosis caused by Francisella orientalis sp. nov. (Fo) and columnaris disease caused by Flavobacterium oreochromis (For) is negatively impacting Nile tilapia (Oreochromis niloticus) production, especially when high stocking densities are used. A new and innovative bivalent mucoadhesive nanovaccine was developed in this study for immersion vaccination of tilapia against francisellosis and columnaris disease. It was shown to have the potential to improve both innate and adaptive immunity in vaccinated Nile tilapia. It increased innate immune parameters, such as lysozyme activity, bactericidal activity, phagocytosis, phagocytic index, and total serum IgM antibody levels. Additionally, the vaccine was effective in elevating specific adaptive immune responses, including IgM antibody levels against Fo and For vaccine antigens and upregulating immune-related genes IgM, IgT, CD4+, MHCIIα, and TCRß in the head kidney, spleen, peripheral blood leukocytes, and gills of vaccinated fish. Furthermore, fish vaccinated with the mucoadhesive nanovaccine showed higher survival rates and relative percent survival after being challenged with either single or combined infections of Fo and For. This vaccine is anticipated to be beneficial for large-scale immersion vaccination of tilapia and may be a strategy for shortening vaccination times and increasing immune protection against francisellosis and columnaris diseases in tilapia aquaculture.