Tilapia culture is an important source of income and nutrition to many rural families. Since 2000, the production of tilapia increased and reached domestic and global markets. Major farmed species is Nile tilapia (Oreochromis niloticus), in earthen ponds and cage cultures. Intensification contributed to global tilapia disease outbreaks, with bacterial infections causing mortalities and morbidities, threatening sustainable production. At tilapia farms, high nutrient concentrations, water temperature and fish densities enhance bacterial growth including virulent bacterial clones and potential zoonotic bacteria. Global warming favours this. This review respectively provides a comprehensive overview of the most common and emerging bacterial pathogens, diseases, clinical presentations and diagnostics of tilapia, including bacteria and diseases with zoonotic potential. First, common bacterial disease outbreaks, including streptococcosis, motileAeromonassepticaemia, francisellosis, columnaris disease and vibriosis are described. Then, information on emerging bacterial infections of concern for tilapia, like edwardsiellosis throughEdwardsiella ictaluriandE.tarda, as well asAeromonas schubertiiis provided. Reports of infectious bacterial tilapia disease outbreaks from other bacteria, includingLactococcus garvieae,Aerococcus viridans,Pseudomonasspp.,Mycobacterium marinumandChlamydiaspp., and others are reviewed. Furthermore, bacteria with zoonotic potential, likeStreptococcus agalactiaeST283,S.iniae,Aeromonassp.,E.tarda,Vibrio vulnificuspathovar (pv)piscisandM.marinumare included in the review, to provide the most current overview of the disease risks affecting production and post‐harvest stages. Additionally, the status and risks of antimicrobial resistance in bacteria from tilapia and other cultured fish through imprudent use of antibiotics, and its future at a global level are provided.

As aquaculture production and the consumption of aquaculture products increase, the possibility of contracting zoonotic infections from either handling or ingesting these products also increases. The principal pathogens acquired topically from fish or shellfish through spine/pincer puncture or open wounds are Aeromonas hydrophila, Edwardsiella tarda, Mycobacterium marinum, Streptococcus iniae, Vibrio vulnificus and V. damsela. These pathogens, which are all indigenous to the aquatic environment, have also been associated with disease outbreaks in food fish. Outbreaks are often related to management factors, such as the quality and quantity of nutrients in the water and high stocking density, which can increase bacterial loads on the external surface of the fish. As a result, diseased fish are more likely to transmit infection to humans. This review provides an account of human cases of zoonoses throughout the world from the principal zoonotic pathogens of fish and shellfish.

Many of the known fish herpesviruses have important aquaculture species as their natural host, and may cause serious disease and mortality. Anguillid herpesvirus 1 (AngHV-1) causes a hemorrhagic disease in European eel, Anguilla anguilla. Despite their importance, fundamental molecular knowledge on fish herpesviruses is still limited. In this study we describe the identification and localization of the structural proteins of AngHV-1. Purified virions were fractionated into a capsid-tegument and an envelope fraction, and premature capsids were isolated from infected cells. Proteins were extracted by different methods and identified by mass spectrometry. A total of 40 structural proteins were identified, of which 7 could be assigned to the capsid, 11 to the envelope, and 22 to the tegument. The identification and localization of these proteins allowed functional predictions. Our findings include the identification of the putative capsid triplex protein 1, the predominant tegument protein, and the major antigenic envelope proteins. Eighteen of the 40 AngHV-1 structural proteins had sequence homologues in related Cyprinid herpesvirus 3 (CyHV-3). Conservation of fish herpesvirus structural genes seemed to be high for the capsid proteins, limited for the tegument proteins, and low for the envelope proteins. The identification and localization of the structural proteins of AngHV-1 in this study adds to the fundamental knowledge of members of the Alloherpesviridae family, especially of the Cyprinivirus genus.

Vibrio vulnificus is a zoonotic pathogen that can cause death by septicaemia in farmed fish (mainly eels) and humans. The zoonotic strains that have been isolated from diseased eels and humans after eel handling belong to clade E (or serovar E (SerE)), a clonal complex within the pathovar (pv.) piscis. The aim of this study was to evaluate the accuracy of MALDI‐TOF mass spectrometry (MS) in the identification of SerE, using the other two main pv. piscis‐serovars (SerA and SerI) from eels as controls. MALDI‐TOF data were compared with known serologic and genetic data of five pv. piscis isolates or strains, and with the non pv. piscis reference strain. Based on multiple spectra analysis, we found serovar‐specific peaks that were of ~3098 Da and ~ 4045 Da for SerE, of ~3085 Da and ~ 4037 Da for SerA, and of ~3085 Da and ~ 4044 Da for SerI. Therefore, our results demonstrate that MALDI‐TOF can be used to identify SerE and could also help in the identification of the other serovars of the species. This means that zoonosis due to V. vulnificus could be prevented by using MALDI‐TOF, as action can be taken immediately after the isolation of a possible zoonotic V. vulnificus strain.

Insect culture has developed rapidly worldwide; it faces important security and safety control issues, including animal infections and disease development. In the Netherlands, in 2021, a ~30% mortality of mealworms, Tenebrio molitor, occurred at one farm, where over-humid sites in the substrate were observed. Bacterial cultures from both the external and internal partsof fry and larger mealworms were identified by MALDI-TOF to predominantly Serratia marcescens, Staphylococcus xylosus and Staphylococus saprofyticus. Due to the important role of S. marcescens as a potential zoonotic bacterium, we performed a molecular characterization of the isolated strain. Genomic analysis showed a multidrug-resistant S. marcescens isolate carrying a tet (41), aac (6′)-Ic, and blaSST-1 chromosomal class C beta-lactamase-resistantgenes, all located on the chromosome. Additionally, several virulence genes were identified. The phylogenetic tree revealed that the S. marcescens strain from this study was similar to other S. marcescens strains from different ecological niches. Although the entomopathogenic activity was not confirmed, this case demonstrates that T. molitor can act as a reservoir and as an alternative path for exposing clinically important antibiotic-resistant bacteria that can affect animals and humans. It underlines the need to keep management factors optimal, before insects and their products enter the feed and food chain.