Selected emerging infectious diseases of ornamental fish

A Review of the Industrial Importance, Common Bacterial Diseases, and Zoonotic Risks of Freshwater Aquarium Fish

Background: The ever-increasing popularity of home aquariums, most often involving freshwater varieties, has exploded in recent years partially due to the Coronavirus pandemic and related to stay-at-home public health precautions for social distancing. With this ever-increasing popularity of aquariums as a hobby, and whether this involves freshwater or marine fish species, a number of important economic, ecological, and public health issues arise for both fish and hobbyists alike. Materials and Methods: This review highlights the history and genesis of aquariums as both a hobby and an important economic factor (industrial, commercial) for many countries on a global basis. Types of aquarium fish are described, and culture conditions leading to homeostasis in aquatic environments are detailed. When these conditions are not met and aquatic systems are out of balance, the disease can result due to stressed fish. Results: Major bacterial diseases associated with freshwater aquarium fish are reviewed, as are potential human infections related to the care and maintenance of home aquaria. Conclusion: Besides, scientific information was also combined with the false facts of hobbyists who tried to identify and treat diseases during an outbreak in the aquarium. Finally, unresolved issues and important misconceptions regarding the field are discussed.

Development of a filter device for the prevention of aquatic bacterial disease using a single-chain variable fragment (scFv)-conjugated affinity silk

Infectious disease is one of the most serious problems in the aquaculture industry for ornamental or edible fish. This study attempted to develop a new device for preventing an aquatic bacterial disease, ulcer disease, caused by Aeromonas salmonicida (As), using “affinity silk”. Affinity silk is a silk protein-containing fibroin L-chain (FibL) fused to the single-chain variable fragment (scFv). It can be easily processed into different formats such as fibers, gels, sponges, or films. A transgenic silkworm that could express a cDNA construct containing FibL fused to an scFv derived from a monoclonal antibody (MAb) against As was successfully generated. An enzyme-linked immunosorbent assay was used to detect As by employing 96-well plates coated with scFv-conjugated affinity silk. As could be captured efficiently by glass wool coated with affinity silk in the column. Furthermore, the air-lift water filter equipped with the affinity silk-coated wool could considerably reduce the concentration of As in water and was estimated to have sufficient ability to trap a lethal dose of As. These findings show that the “affinity silk filter” is a potential device for the prophylaxis of aquatic animal diseases.

Investigation of Cyprinid Herpesvirus 3 (CyHV-3) Disease Periods and Factors Influencing CyHV-3 Transmission in A Low Stocking Density Infection Trial

Simple Summary

Pathogens are the primary limitation to aquaculture production of fish and a major issue in consideration of the interface between cultured and wild populations of fishes worldwide. While rapid spread of fish pathogens between populations (wild or farmed) is generally anthropogenic and the result of trade, the mechanisms of transmission once a pathogen has been introduced to a fish population are not well understood. The most widespread pathogen impacting both aquaculture and wild populations of common carp (Cyprinus carpio, carp) is Cyprinid herpesvirus 3 (CyHV-3). To understand how CyHV-3 is transmitted in a population we conducted a series of infection trials, designed to determine the kinetics CyHV-3 infections, identify the contributions of direct and indirect forms of CyHV-3 transmission, and to determine the contributions of contact rate, viral load, pathogenicity, and contact type. We found that direct contact between fish was the primary mechanism of CyHV-3 transmission rather than transmission through contaminated water. Additionally, CyHV-3 transmission occurred primarily during the incubation period of CyHV-3, prior to the appearance of disease signs and disease-associated reduction in contact rate.

Abstract

Cyprinid herpesvirus 3 (CyHV-3) is the etiological agent of koi herpesvirus disease (KHVD) and important pathogen of aquaculture and wild populations of common carp worldwide. Understanding the relative contributions of direct and indirect transmission of CyHV-3 as well as the factors that drive CyHV-3 transmission can clarify the importance of environmental disease vectors and is valuable for informing disease modeling efforts. To study the mechanisms and factors driving CyHV-3 transmission we conducted infection trials that determined the kinetics of KHVD and the contributions of direct and indirect forms of CyHV-3 transmission, as well as the contributions of contact rate, viral load, pathogenicity and contact type. The incubation period of KHVD was 5.88 + 1.75 days and the symptomatic period was 5.31 + 0.87 days. Direct transmission was determined to be the primary mechanism of CyHV-3 transmission (OR = 25.08, 95%CI = 10.73–99.99, p = 4.29 × 10⁻¹⁸) and transmission primarily occurred during the incubation period of KHVD. Direct transmission decreased in the symptomatic period of disease. Transmissibility of CyHV-3 and indirect transmission increased during the symptomatic period of disease, correlating with increased viral loads. Additionally, potential virulence-transmission tradeoffs and disease avoidance behaviors relevant to CyHV-3 transmission were identified.

Systemic phaeohyphomycosis in splitnose rockfish (Sebastes diploproa) caused by Devriesia sp

A novel pathogen was documented after two wild-caught, juvenile, splitnose rockfish presented with buphthalmia, grey corneal endothelial plaques and evidence of uveitis. Cytologic evaluation of ocular contents revealed fungal hyphae. Histologic evaluation identified multiple fungal granulomas and granulomatous inflammation in the globes, periocular tissue and heart. Fungi were slender, hyphenated and branched at angles, had parallel cell walls and had brown pigmentation in haematoxylin- and eosin-stained sections. Both fish were diagnosed with phaeohyphomycosis. Culture with nuclear ribosomal RNA internal transcribed spacer (ITS) segment identification further classified the fungus as Devriesia sp., which has not been previously documented as a cause of disease in animals.

Prevalence of antibiotic resistance genes in wastewater collected from ornamental fish market in northern China

Large amounts of antibiotics/disinfectants are used in the farming of ornamental fish so as to prevent and treat bacterial infection. This may exert considerable selection pressures on the prevalence and propagation of antibiotic resistance genes (ARGs). However, the levels of ARGs and their potential prevalence mechanism in the wastewater of the ornamental fish industry remains unclear. In this work, wastewater is collected from a representative ornamental fish market (OFM) that is located at the northern China to study the occurrence and abundance of 21 ARGs and 2 integrase genes. Results indicated that 15 different ARGs and 2 integrase genes are existent and prevalent in the wastewater of OFM, whereby concentrations range from 2.01 to 10.34 copies/L. Proteobacteria, Bacteroidetes, Verrucomicrobia, and Firmicutes are the predominant phyla in the wastewater samples. 17 species of human opportunistic pathogens are present with relative abundance of up to 0.01%, which suggests a considerable risk of pathogens acquiring and disseminating ARGs. Moreover, oxytetracycline, ciprofloxacin, norfloxacin, sulfadiazine, and chloramphenicol are most frequently detected in wastewater, with concentrations of up to 1150, 877, 514, 1970, and 1700 ng/L, respectively. Notably, good correlations have been determined among ARGs and antibiotics, non-antibiotic environmental factors in wastewater of OFM. This current study reveals, for the first time, that OFM is a previously unperceived reservoir for ARG prevalence in aquatic environment and water environmental factors (particularly antibiotics), and their induced shifts in the microbial communities are the key factors for distribution of ARGs in OFM.

Updates on Selected Emerging Infectious Diseases of Ornamental Fish

Emerging infectious diseases of ornamental fish are discussed with special focus on clinical relevance, detection, and treatment, where applicable. Important emerging infectious diseases of fish include goldfish herpesvirus, koi herpesvirus, carp edema virus, Erysipelothrix, Edwardsiella ictaluri, Edwardseilla piscicida, and Francisella. Some diseases are more species or genus specific, but many emerging diseases do not seem to have a species preference and affect a variety of species worldwide. Proper husbandry and biosecurity with a disease detection plan for ornamental fish is essential to monitor and prevent future outbreaks.

Exploring the Diversity Within the Genus Francisella - An Integrated Pan-Genome and Genome-Mining Approach

Pan-genome analysis is a powerful method to explore genomic heterogeneity and diversity of bacterial species. Here we present a pan-genome analysis of the genus Francisella, comprising a dataset of 63 genomes and encompassing clinical as well as environmental isolates from distinct geographic locations. To determine the evolutionary relationship within the genus, we performed phylogenetic whole-genome studies utilizing the average nucleotide identity, average amino acid identity, core genes and non-recombinant loci markers. Based on the analyses, the phylogenetic trees obtained identified two distinct clades, A and B and a diverse cluster designated C. The sizes of the pan-, core-, cloud-, and shell-genomes of Francisella were estimated and compared to those of two other facultative intracellular pathogens, Legionella and Piscirickettsia. Francisella had the smallest core-genome, 692 genes, compared to 886 and 1,732 genes for Legionella and Piscirickettsia respectively, while the pan-genome of Legionella was more than twice the size of that of the other two genera. Also, the composition of the Francisella Type VI secretion system (T6SS) was analyzed. Distinct differences in the gene content of the T6SS were identified. In silico approaches performed to identify putative substrates of these systems revealed potential effectors targeting the cell wall, inner membrane, cellular nucleic acids as well as proteins, thus constituting attractive targets for site-directed mutagenesis. The comparative analysis performed here provides a comprehensive basis for the assessment of the phylogenomic relationship of members of the genus Francisella and for the identification of putative T6SS virulence traits.

A review of the helminths co-introduced with Trachemys scripta elegans – a threat to European native turtle health

In the 20th century large numbers of exotic turtles Trachemys scripta elegans have been imported into Europe as pets and this has led to frequent introductions into many freshwater ecosystems. Nowadays, established populations of red-eared slider, coexist and compete with the native in Europe species of turtles in the wild. Invasive turtles are a threat to indigenous species because of carriage of many parasites, which are often considered to cause disease emergence and produce high mortality in native hosts. Helminths are the most prominent group introduced with T. s. elegans and due to their host-switching ability have become important co-invaders, a potential threat to indigenous turtle health. The aim of this review was to assess the risks of the transfer of helminths co-introduced with T. s. elegans to native species of European turtles.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): Koi herpes virus disease (KHV)

Koi herpes virus (KHV) disease has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of KHV disease to be listed, Article 9 for the categorisation of KHV disease according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to KHV disease. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, it is inconclusive whether KHV disease can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL because there was no full consensus on the criterion 5 A(v). Consequently, the assessment on compliance of KHV disease with the criteria as in Annex IV of the AHL, for the application of the disease prevention and control rules referred to in Article 9(1) is also inconclusive, as well as which animal species can be considered to be listed for KHV disease according to Article 8(3) of the AHL.

Whole-Genome Relationships among Francisella Bacteria of Diverse Origins Define New Species and Provide Specific Regions for Detection

Francisella tularensis is a highly virulent zoonotic pathogen that causes tularemia and, because of weaponization efforts in past world wars, is considered a tier 1 biothreat agent. Detection and surveillance of F. tularensis may be confounded by the presence of uncharacterized, closely related organisms. Through DNA-based diagnostics and environmental surveys, novel clinical and environmental Francisella isolates have been obtained in recent years. Here we present 7 new Francisella genomes and a comparison of their characteristics to each other and to 24 publicly available genomes as well as a comparative analysis of 16S rRNA and sdhA genes from over 90 Francisella strains. Delineation of new species in bacteria is challenging, especially when isolates having very close genomic characteristics exhibit different physiological features-for example, when some are virulent pathogens in humans and animals while others are nonpathogenic or are opportunistic pathogens. Species resolution within Francisella varies with analyses of single genes, multiple gene or protein sets, or whole-genome comparisons of nucleic acid and amino acid sequences. Analyses focusing on single genes (16S rRNA, sdhA), multiple gene sets (virulence genes, lipopolysaccharide [LPS] biosynthesis genes, pathogenicity island), and whole-genome comparisons (nucleotide and protein) gave congruent results, but with different levels of discrimination confidence. We designate four new species within the genus; Francisella opportunistica sp. nov. (MA06-7296), Francisella salina sp. nov. (TX07-7308), Francisella uliginis sp. nov. (TX07-7310), and Francisella frigiditurris sp. nov. (CA97-1460). This study provides a robust comparative framework to discern species and virulence features of newly detected Francisella bacteria.

IMPORTANCE

DNA-based detection and sequencing methods have identified thousands of new bacteria in the human body and the environment. In most cases, there are no cultured isolates that correspond to these sequences. While DNA-based approaches are highly sensitive, accurately assigning species is difficult without known near relatives for comparison. This ambiguity poses challenges for clinical cases, disease epidemics, and environmental surveillance, for which response times must be short. Many new Francisella isolates have been identified globally. However, their species designations and potential for causing human disease remain ambiguous. Through detailed genome comparisons, we identified features that differentiate F. tularensis from clinical and environmental Francisella isolates and provide a knowledge base for future comparison of Francisella organisms identified in clinical samples or environmental surveys.

Anatomy and Disorders of the Oral Cavity of Ornamental Fish

Ornamental fish represent the largest and most diverse group of exotic animals kept as pets. The specific oral anatomy of each family or selected species has evolved to suit the natural environment, feeding behaviors, food or prey type, and location of the food/prey in the water column. The anatomy can change over the life of the animal, from fry to adult. The oral cavity of fish is susceptible to many problems including infectious and parasitic diseases, trauma, and neoplasia. Diagnosis may involve wet mount preparations of exfoliative cytology from the lesion, histopathology, and bacterial or fungal culture.