Transmission of Mycobacterium chelonae and Mycobacterium marinum in laboratory zebrafish through live feeds

Diagnosis of piscine francisellosis in Largemouth Bass from a public display exhibit in north-central Florida, USA

OBJECTIVE

The Largemouth Bass Micropterus salmoides is an important freshwater fish that is native to the southeastern United States and is cultured for conservation, food, and for the sports fishing industry. Francisella orientalis is a globally distributed bacterial pathogen of warmwater fish species and is associated with granulomatous inflammation and high mortalities. Outbreaks of piscine francisellosis in the United States have been reported in only a few fish species. This study describes three case presentations of francisellosis in Largemouth Bass from a public display system in north-central Florida. Additionally, laboratory-controlled immersion challenges using an F. orientalis isolate from tilapia Oreochromis spp. evaluate susceptibility of Largemouth Bass fingerlings to F. orientalis infection and mortality through this exposure route.

METHODS

Necropsy, histologic examination, immunohistochemistry, bacterial recovery and culture, and quantitative polymerase chain reaction were used as diagnostic tools to evaluate both the affected display fish and the immersion-challenged fingerlings.

RESULT

Although the display fish and immersion-challenged fingerlings presented with nonspecific clinical signs, gross and histological changes were indicative of granulomatous disease. Immunohistochemical and molecular testing methods confirmed F. orientalis infection in affected fish.

CONCLUSION

The three case presentations described here mark the first reporting of naturally occurring piscine francisellosis in Largemouth Bass that were held in a public display exhibit. Additionally, causality was proven in the Largemouth Bass fingerlings through the immersion challenges. These findings demonstrate susceptibility through immersion-based exposure and assert that francisellosis should be considered among the list of differential diagnoses for Largemouth Bass with granulomatous disease.

Pathological Manifestations of Francisella orientalis in the Green Texas Cichlid (Herichthys cyanoguttatus)

Simple Summary

The following study demonstrates the pathological manifestations of an emerging virulent bacterium, Francisella orientalis, in an ornamental cichlid fish, the green Texas cichlid (Herichthys cyanoguttatus). This study was conducted to prove that Francisella orientalis can cause a disease in the green Texas cichlid that is similar to natural infection. Francisella orientalis was discovered for the first time in green Texas cichlid by our team in Taiwan in 2015. The present study simply tried to prove the susceptibility of Francisella orientalis in green Texas cichlid by conducting a challenge experiment, where healthy fish were injected with a dose of the bacteria. After the challenge, the healthy fish showed the same disease progression as was seen in the case of natural outbreak. The mortality rate, clinical symptoms, gross findings, and histopathological findings were similar to natural infection. Francisella orientalis could also be recovered in artificial media from challenged fish, thus indicating that the bacteria had multiplied inside the fish. These findings prove that green Texas cichlid (Herichthys cyanoguttatus) is susceptible to Francisela orientalis, and new management and vaccination strategies are necessary in the farming of this fish. This study also helps by adding to the knowledge of the growing host base for Francisella orientalis.

Abstract

Francisella orientalis (Fo) is considered to be one of the major pathogens of tilapia because of the high mortalities observed during outbreaks. Other cichlids belonging to the same family (Cichlidae) as tilapia are also quite susceptible to this pathogen. On various occasions, Fo has also been isolated from other warm water fish, including three-line grunt, hybrid striped bass, French grunt, Caesar grunt, and Indo-Pacific reef fish. However, only a few studies have reported the pathogenicity of Francisella orientalis in ornamental cichlid fish. This study fulfills Koch’s postulates by showing that a strain of Fo obtained from green Texas cichlid (Herichthys cyanoguttatus) was able to produce the same pathogenicity in healthy fish. A mortality of 100% was observed after healthy green Texas cichlid were experimentally injected with Fo at a dose of 8.95 × 10⁵ CFU/fish. DNA extracted from the organs of predilection (spleen, head kidney) gave positive results by PCR for all fish that died during the experimental period. Spleen and head kidney presented with multifocal white nodules in the affected fish, corresponding to typical vacuolated granulomas on histopathological examination of the tissues. Based on the results of this study, it is evident that Fo can indeed infect green Texas cichlid and produce a disease typical of francisellosis.

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.

Comparison of the pathogenicity of Francisella orientalis in Nile tilapia (Oreochromis niloticus), Asian seabass (Lates calcarifer) and largemouth bass (Micropterus salmoides) through experimental intraperitoneal infection

Francisella orientalis is a highly virulent, emerging bacterium that causes mass mortalities in tilapia. This pathogen also affects numerous other warm-water fish species, including three-line grunt, hybrid striped bass and various ornamental fish. This study sheds light on two new species of fish that are susceptible to F. orientalis. Asian seabass and largemouth bass showed variable levels of susceptibility in a bacterial challenge experiment. After intraperitoneally injected with a dose of 10⁶  CFU/fish, a total of 64.28% and 21.42% mortalities were obtained in Asian seabass and largemouth bass, respectively. Meanwhile, Nile tilapia showed acute mortality of 100%. All fish showed typical lesions of francisellosis, including multifocal granulomas in the spleen and head kidney. Immunohistochemical analysis revealed strong positive signals inside the granulomas of all fish. The bacterial recovery in solid media from infected fish was highest in Nile tilapia (85.71%), followed by Asian seabass (35.71%) and largemouth bass (21.42%). PCR results tested 100% positive for Nile tilapia, and 78.57% and 21.42% for Asian seabass and largemouth bass, respectively. In conclusion, Asian seabass and largemouth bass are susceptible to this pathogen, which warrants new management strategies when employing predation polyculture systems of these species with tilapia.

Review of diseases and health management in zebrafish Danio rerio (Hamilton 1822) in research facilities

The use of zebrafish (Danio rerio) in biomedical research has expanded at a tremendous rate over the last two decades. Along with increases in laboratories using this model, we are discovering new and important diseases. We review here the important pathogens and diseases based on some 20 years of research and findings from our diagnostic service at the NIH-funded Zebrafish International Resource Center. Descriptions of the present status of biosecurity programmes and diagnostic and treatment approaches are included. The most common and important diseases and pathogens are two parasites, Pseudoloma neurophilia and Pseudocapillaria tomentosa, and mycobacteriosis caused by Mycobacterium chelonae, M. marinum and M. haemophilum. Less common but deadly diseases are caused by Edwardsiella ictaluri and infectious spleen and kidney necrosis virus (ISKNV). Hepatic megalocytosis and egg-associated inflammation and fibroplasia are common, apparently non-infectious, in zebrafish laboratories. Water quality diseases include supersaturation and nephrocalcinosis. Common neoplasms are spindle cell sarcomas, ultimobranchial tumours, spermatocytic seminomas and a small-cell carcinoma that is caused by a transmissible agent. Despite the clear biosecurity risk, researchers continue to use fish from pet stores, and here, we document two novel coccidia associated with significant lesions in zebrafish from one of these stores.

Review of diseases and health management in zebrafish Danio rerio (Hamilton 1822) in research facilities

The use of zebrafish (Danio rerio) in biomedical research has expanded at a tremendous rate over the last two decades. Along with increases in laboratories using this model, we are discovering new and important diseases. We review here the important pathogens and diseases based on some 20 years of research and findings from our diagnostic service at the NIH-funded Zebrafish International Resource Center. Descriptions of the present status of biosecurity programmes and diagnostic and treatment approaches are included. The most common and important diseases and pathogens are two parasites, Pseudoloma neurophilia and Pseudocapillaria tomentosa, and mycobacteriosis caused by Mycobacterium chelonae, M. marinum and M. haemophilum. Less common but deadly diseases are caused by Edwardsiella ictaluri and infectious spleen and kidney necrosis virus (ISKNV). Hepatic megalocytosis and egg-associated inflammation and fibroplasia are common, apparently non-infectious, in zebrafish laboratories. Water quality diseases include supersaturation and nephrocalcinosis. Common neoplasms are spindle cell sarcomas, ultimobranchial tumours, spermatocytic seminomas and a small-cell carcinoma that is caused by a transmissible agent. Despite the clear biosecurity risk, researchers continue to use fish from pet stores, and here, we document two novel coccidia associated with significant lesions in zebrafish from one of these stores.

Morphology and 18S rDNA sequencing of Henneguya peruviensis n. sp. (Cnidaria: Myxosporea), a parasite of the Amazonian ornamental fish Hyphessobrycon loretoensis from Peru: A myxosporean dispersal approach

Myxosporean are endoparasitic cnidarians of wide distribution and responsible for important economic losses in fisheries and aquaculture. A new myxosporean species, Henneguya peruviensis n. sp., is herein described as obtained from the gill filaments of Hyphessobrycon loretoensis caught in the Nanay River, Department of Loreto, Peru. The parasite was found in 37 of 45 (82.2%) examined H. loretoensis. The new species was characterized based on morphological features and 18S rDNA gene sequence data. The sequencing of the 18S rDNA gene from the spores of H. peruviensis n. sp. resulted in 1632 nucleotides and this sequence did not match any of the myxozoan available in the GenBank. Phylogenetic analysis showed that H. peruviensis n. sp. closed together with H. leporinicola. Nonetheless, the 18S rDNA sequences of H. peruviensis n. sp. and H. leporinicola have only 82% similarity. This is the first description and molecular study of a Myxozoa parasitizing fish of the genus Hyphessobrycon in the Amazon basin. Given the importance of the ornamental fish industry in translocation of aquatic organisms worldwide, the international movement of myxosporeans in infected fish is discussed in terms of disease outbreaks and the need for preventative action.

Development of a recombinase polymerase amplification assay for rapid detection of Francisella noatunensis subsp. orientalis

Francisella noatunensis subsp. orientalis (Fno) is the causative agent of piscine francisellosis in warm water fish including tilapia. The disease induces chronic granulomatous inflammation with high morbidity and can result in high mortality. Early and accurate detection of Fno is crucial to set appropriate outbreak control measures in tilapia farms. Laboratory detection of Fno mainly depends on bacterial culture and molecular techniques. Recombinase polymerase amplification (RPA) is a novel isothermal technology that has been widely used for the molecular diagnosis of various infectious diseases. In this study, a recombinase polymerase amplification (RPA) assay for rapid detection of Fno was developed and validated. The RPA reaction was performed at a constant temperature of 42°C for 20 min. The RPA assay was performed using a quantitative plasmid standard containing a unique Fno gene sequence. Validation of the assay was performed not only by using DNA from Fno, closely related Francisella species and other common bacterial pathogens in tilapia farms, but also by screening 78 Nile tilapia and 5 water samples. All results were compared with those obtained by previously established real-time qPCR. The developed RPA showed high specificity in detection of Fno with no cross-detection of either the closely related Francisella spp. or the other tested bacteria. The Fno-RPA performance was highly comparable to the published qPCR with detection limits at 15 and 11 DNA molecules detected, respectively. The RPA gave quicker results in approximately 6 min in contrast to the qPCR that needed about 90 min to reach the same detection limit, taking only 2.7–3 min to determine Fno in clinical samples. Moreover, RPA was more tolerant to reaction inhibitors than qPCR when tested with field samples. The fast reaction, simplicity, cost-effectiveness, sensitivity and specificity make the RPA an attractive diagnostic tool that will contribute to controlling the infection through prompt on-site detection of Fno.

Targeted Drug Delivery and Treatment of Endoparasites with Biocompatible Particles of pH-Responsive Structure

Biomaterials conceived for vectorization of bioactives are currently considered for biomedical, biological, and environmental applications. We have produced a pH-sensitive biomaterial composed of natural source alginate and chitosan polysaccharides for application as a drug delivery system via oral administration. The composite particle preparation was in situ monitored by means of isothermal titration calorimetry. The strong interaction established between the macromolecules during particle assembly led to 0.60 alginate/chitosan effective binding sites with an intense exothermic effect and negative enthalpy variation on the order of a thousand kcal/mol. In the presence of model drugs mebendazole and ivermectin, with relatively small and large structures, respectively, mebendazole reduced the amount of chitosan monomers available to interact with alginate by 27%, which was not observed for ivermectin. Nevertheless, a state of intense negative Gibbs energy and large entropic decrease was achieved, providing evidence that formation of particles is thermodynamically driven and favored. Small-angle X-ray scattering provided further evidence of similar surface aspects independent of the presence of drug. The physical responses of the particles to pH variation comprise partial hydration, swelling, and the predominance of positive surface charge in strong acid medium, whereas ionization followed by deprotonation leads to compaction and charge reversal rather than new swelling in mild and slightly acidic mediums, respectively. In vivo performance was evaluated in the treatment of endoparasites in Corydoras fish. Systematically with a daily base oral administration, particles significantly reduced the infections over 15 days of treatment. The experiments provide evidence that utilizing particles granted and boosted the action of the antiparasitic drugs, leading to substantial reduction or elimination of infection. Hence, the pH-responsive particles represent a biomaterial with prominent characteristics that is promising for the development of targeted oral drug delivery.

Locally extensive meningoencephalitis caused by Miamiensis avidus (syn. Philasterides dicentrarchi) in a zebra shark

Scuticociliatosis, caused by ciliated protozoa in the subclass Scuticociliatia of the phylum Ciliophora, can cause fatal disease in teleost fish species. However, information on scuticociliatosis in elasmobranchs is still scarce. In this report, we describe a case of locally extensive meningoencephalitis caused by Miamiensis avidus (syn. Philasterides dicentrarchi) in a 2 yr old captive zebra shark Stegostoma fasciatum. Granulocytic meningoencephalitis was observed through histological assessment. Inflammation was confined to the ventral aspect of the brain with a large number of ciliated protozoa, transforming into non-suppurative meningitis in the lateral aspect, and gradually vanished in the dorsal aspect. No histopathological and polymerase chain reaction (PCR) evidence of systemic dissemination of M. avidus was found. PCR targeting the gene coding the small-subunit ribosomal RNA (SSUrRNA) of M. avidus was performed on the brain, liver, and gill tissues, and only brain tissue yielded a positive result. The DNA sequences from amplicons of the protozoal SSUrRNA gene were completely matched to that of M. avidus. The distribution of protozoa in the current case was mainly located in the brain and suggests the possibility of a direct neural invasive pathway of M. avidus through the nasal cavity/ampullary system and/or a unique tissue tropism of M. avidus specific to the brain in zebra sharks. Further investigations on the pathogenesis of M. avidus in elasmobranchs, especially zebra sharks, are needed.

Evolution of the Marrow Adipose Tissue Microenvironment

Adipocytes of the marrow adipose tissue (MAT) are distributed throughout the skeleton, are embedded in extracellular matrix, and are surrounded by cells of the hematopoietic and osteogenic lineages. MAT is a persistent component of the skeletal microenvironment and has the potential to impact local processes including bone accrual and hematopoietic function. In this review, we discuss the initial evolution of MAT in vertebrate lineages while emphasizing comparisons to the development of peripheral adipose, hematopoietic, and skeletal tissues. We then apply these evolutionary clues to define putative functions of MAT. Lastly, we explore the regulation of MAT by two major components of its microenvironment, the extracellular matrix and the nerves embedded within. The extracellular matrix and nerves contribute to both rapid and continuous modification of the MAT niche and may help to explain evolutionary conserved mechanisms underlying the coordinated regulation of blood, bone, and MAT within the skeleton.

Susceptibility of common carp and sunfish to a strain of Francisella noatunensis subsp. orientalis in a challenge experiment

Francisellosis, an emerging disease in many fish species, can cause high mortality in affected populations. Here we investigated the susceptibility of common carp Cyprinus carpio and sunfish Lepomis gibbosus to Francisella noatunensis subsp. orientalis (Fno), and possible transmission of the bacteria between the 2 fish species. In a challenge experiment, 3 groups of each species were injected intraperitoneally (IP) with 3 different doses of an Fno strain no. 9449 of the Norwegian Veterinary Institute, recovered from naturally infected ornamental Malawi cichlids. Infected carp were cohabitated with sunfish and vice versa. Control groups were injected with 0.9M phosphate-buffered saline and cohabitated accordingly. Fish were sampled at different time points. Mortality of challenged sunfish was observed during the first 96 h and reached 56.1%. In the control sunfish, 4 of 16 fish (25%) died within 48 h. In carp, no mortalities or clinical signs were observed during the experiment. General clinical and patho-anatomical disease signs of affected sunfish were observed. We detected granulomas in 2 cohabitated sunfish and 1 challenged carp, but could not re-isolate Fno from these fish. Fno was successfully cultured from 6 sunfish and 3 carp specimens until 35 d post injection. PCR of spleen and kidney with 16S rDNA Francisella-like bacterium primers 180f and 485r yielded amplicons in 68.3% of challenged sunfish and only 12.2% of challenged carp. We demonstrated that sunfish were susceptible to Fno infection while the carp were not. Horizontal transmission of the agent between the 2 fish species could not be demonstrated.

FIRST ISOLATION OF TENACIBACULUM MARITIMUM IN A CAPTIVE SAND TIGER SHARK (CARCHARIAS TAURUS)

This report describes a case of the first isolation of Tenacibaculum maritimum from a captive-bred adult female sand tiger shark (Carcharias taurus) housed at the Cattolica Aquarium (Italy). The animal showed, between the second dorsal fin and the precaudal pit, skin lesions characterized by the presence of abundant whitish necrotic tissue. Through routine bacteriological examination, a bacterium was isolated from a skin lesion and subsequently identified as T. maritimum by phenotypic characters and species-specific polymerase chain reaction. The antimicrobial sensitivity of the isolated strain was evaluated for 11 antimicrobial agents by disk diffusion method. Antibiotic therapy was conducted with enrofloxacin at 10 mg kg(-1) i.m. on alternate days for 10 days. One month after the end of treatment skin lesions showed complete resolution and the shark recovered completely. The case presented here represents the first report of infection by T. maritimum in a sand tiger shark and highlights the potential pathogenic role of this microorganism in elasmobranchs kept in an aquarium.

Francisellosis in fish: an emerging challenge

Francisellosis is a bacterial disease with increasing economic impacts in the culture of tilapia and Atlantic cod since emerging in 1992. Two main strains – Francisella noatunensis subsp. orientalis (Fno) and F. noatunensis subsp. noatunensis (Fnn), have been identified, causing both acute and chronic granulomatous systemic disease. The piscine host range is increasing and Francisella culture should be included in routine diagnosis. Differentiation from the major zoonotic F. tularensis and opportunistic zoonotic F. philomiragia when dealing with environmental soil and water samples from fish farms is important. Diagnosis can be challenging but presentation of granulomatous pathology in fish should require use of cysteine supplemented selective media, culture at 15–28°C or culture in fish cell lines and specific PCR to exclude piscine Fno or Fnn. Control of infections in fish rely on appropriate antibiotic selection although in the long term an effective commercial vaccine that includes the pathogenic species of Francisella is required.

Identification of Francisella noatunensis in novel host species French grunt (Haemulon flavolineatum) and Caesar grunt (Haemulon carbonarium)

Francisella noatunensis is an emerging pathogen of fish that has been isolated from several cultured species worldwide. Here presented is a case involving several hundred marine grunts that were caught near the Florida Keys for display in public aquaria. These fish were maintained in a recirculating system where they began to experience mortalities approximately two weeks post-stocking. Postmortem examination revealed disseminated systemic granulomatous disease most severely affecting spleen and kidney. Splenic and renal tissue homogenates inoculated in modified Thayer Martin agar media yielded colonies consistent with F. noatunensis 4 days post inoculation. Bacterial colonies and tissues were confirmed positive after real-time PCR amplification of the intracellular growth loci gene (iglC) specific for F. noatunensis subspecies orientalis. Consequently, multiple novel host species for this pathogen were identified, including the French grunt (Haemulon flavolineatum) and the Caesar grunt (Haemulon carbonarium).