Non-antibiotic approaches to combat motile Aeromonas infections in aquaculture: Current state of knowledge and future perspectives

Inland aquaculture contributed by three major fish groups, including carps, tilapias, and catfish plays a vital role in global food security and nutrition, particularly in low and middle-income countries. However, the sustainable development of this sector is hampered by disease epidemics, especially those caused by bacteria such as Aeromonas species. At least eight pathogenic motile Aeromonas species (A. hydrophila, A. veronii, A. jandaei, A. caviae, A. sobria, A. bestiarum, A. dhakensis and A. schubertii) have been reported in aquaculture with some causing up to 100% mortality during disease outbreaks. Simultaneously, emerging multidrug-resistant Aeromonas due to a long-inappropriate use of antibiotics is alarming and highlights a global public health concern and negative socioeconomic impacts. Here, we provide a comprehensive overview of motile Aeromonas infections, antibiotic use and antimicrobial resistance of Aeromonas species. This contribution also highlights the non-antibiotic approaches (the solutions for preventing or treating of bacterial diseases without resorting to antibiotic use) to control motile Aeromonas infections. In addition to the current state of knowledge and limitations of each prophylaxis/therapy, perspectives for future research are discussed critically, including oral/immersion multivalent vaccines, microencapsulated synbiotics, exogenous metabolites, and novel lytic bacteriophage cocktails. Some emerging applicable nanotechnology themes such as nanovaccines, nanobioactive compounds, and nanobubbles are also included in this review. In summary, combating motile Aeromonas infections in aquaculture, including multidrug-resistant aeromonads, as well as other bacterial diseases, is a lengthy battle that requires a strategic combination of multiple non-antibiotic approaches coherent with the One Health philosophy

First evidence of scale drop disease virus in farmed Asian seabass (Lates calcarifer) in Malaysia

An unknown disease event in marine cage-cultured Asian seabass (Lates calcarifer) was observed in Malaysia in September 2019, which affected adult-sized fish and resulted in significant mortality. Affected fish showed gross signs resembling scale drop disease such as lethargy, darkened dorsal part of the body, easily detached scales, severe scale loss, reddening and hemorrhage at the ventral part of the body, and tendency to swim at the water surface. Histopathological examinations revealed abnormal changes in multiple internal organs including vacuolated cytoplasm hepatocytes, necrotic kidney tubules, atrophied glomeruli, blood congestion and hemorrhage in the spleen and brain, as well as penetration of lymphocytic inflammatory cells. Notably, basophilic hypertrophied cells and intracytoplasmic inclusion bodies were occasionally observed in the liver, indicating suspected viral aetiology. Transmission electron microscopy (TEM) revealed the presence of multiple viral particles in the cytoplasm of the infected cells. Subsequently, PCR and sequence analyses revealed that all affected fish were positive to scale drop disease virus (SDDV), which was absent from the clinically healthy fish. Phylogeny analysis based on complete ORF 060 L (encoding major capsid protein) revealed high similarity between the SDDV from Malaysia, Thailand and Singapore. This study provides first evidence of SDDV infection in cultured Asian seabass in Malaysia. We thus recommend that active surveillance should be prioritized for concentrated Asian seabass farming areas in Malaysia to prevent spread of the disease nation-wide

Complete Genome Sequence of the Marine Fish Pathogen Vibrio anguillarum Harboring the pJM1 Virulence Plasmid and Genomic Comparison with Other Virulent Strains of V. anguillarum and V. ordalii ▿ †

We dissected the complete genome sequence of the O1 serotype strain Vibrio anguillarum 775(pJM1) and determined the draft genomic sequences of plasmidless strains of serotype O1 (strain 96F) and O2β (strain RV22) and V. ordalii. All strains harbor two chromosomes, but 775 also harbors the virulence plasmid pJM1, which carries the anguibactin-producing and cognate transport genes, one of the main virulence factors of V. anguillarum. Genomic analysis identified eight genomic islands in chromosome 1 of V. anguillarum 775(pJM1) and two in chromosome 2. Some of them carried potential virulence genes for the biosynthesis of O antigens, hemolysins, and exonucleases as well as others for sugar transport and metabolism. The majority of genes for essential cell functions and pathogenicity are located on chromosome 1. In contrast, chromosome 2 contains a larger fraction (59%) of hypothetical genes than does chromosome 1 (42%). Chromosome 2 also harbors a superintegron, as well as host “addiction” genes that are typically found on plasmids. Unique distinctive properties include homologues of type III secretion system genes in 96F, homologues of V. cholerae zot and ace toxin genes in RV22, and the biofilm formation syp genes in V. ordalii. Mobile genetic elements, some of them possibly originated in the pJM1 plasmid, were very abundant in 775, resulting in the silencing of specific genes, with only few insertions in the 96F and RV22 chromosomes

Efficacy of a combination product containing pyrantel, febantel and praziquantel (DrontalA (R) Plus Flavour, Bayer Animal Health) against experimental infection with the hookworm Ancylostoma ceylanicum in dogs

Ancylostoma ceylanicum is a common hookworm of dogs, cats and humans in Asia. More recently, this hook-worm was found to infect dogs in Australia. The objective of this study was to determine the efficacy of a combination product containing pyrantel, febantel and praziquantel (Drontal® Plus Flavour, Bayer) against A. ceylanicum in experimentally infected dogs. Twelve dogs were each subcutaneously injected with 300 infective third-stage larvae of A. ceylanicum. Pups were stratified by egg count and randomly allocated equally into control and treatment groups. The pups in the treatment group were treated orally at 20 days post-infection with a tablet containing pyrantel, febantel and praziquantel (Drontal® Plus Flavour, Bayer) with the recommended dose of one tablet per 10 kg bodyweight. The dogs in the control group were not treated. Egg counts were performed daily until the end of the study period and compared for the treated and control groups. No eggs were detected in the treated group of pups within 3 days of treatment, and faecal samples from this group remained negative throughout the rest of the study resulting in a treatment efficacy (egg reduction) of 100% (p=0.0011). The egg counts for the untreated group remained high for the rest of the study period. This trial demonstrated that a combination tablet containing pyrantel, febantel and praziquantel (Drontal® Plus Flavour, Bayer) given at the manufacturer's recommended dose is effective against infection with A. ceylanicum in dogs