Diseases of aquatic organisms最新文献

NK-lysin is an effective antimicrobial peptide secreted by natural killer (NK) cells and cytotoxic T lymphocytes. Although numerous studies have been conducted on NK-lysin, its biological functions have not yet been comprehensively catalogued. In this study, a novel NK-lysin peptide, NKLj27, located in the SapB domain of Japanese seabass Lateolabrax japonicus, was identified and synthesized, and its antibacterial and chemotactic activities were investigated. Bioinformatic analyses showed that NKLj27 shared 66.67-79.17% sequence homology with known teleost NK-lysin peptides, and the spatial structure prediction of NKLj27 indicated that it was mainly composed of α-helices. A subsequent antibacterial assay demonstrated that NKLj27 exhibits potent activity against Staphylococcus aureus, Micrococcus luteus, Vibrio litoralis, V. alginolyticus, Listonella anguillarum, Escherichia coli, V. harveyi, and V. scophthalmi. During the interaction with V. alginolyticus, NKLj27 changed the cell membrane permeability, causing leakage of cellular contents, while the cell membrane structure remained basically intact; subsequently, NKLj27 penetrated into the cytoplasm and acted on bacterial nucleic acids. It first bound to bacterial genomic DNA and RNA, then caused their retardation and degradation, and following incubation, it changed the physical conformation of the DNA molecules. The in vivo experiments showed that NKLj27 significantly reduced V. alginolyticus load in fish tissues. At the cellular level, NKLj27 also exhibited chemotactic activity on epithelioma papulosum cyprini cells. In summary, these results provide new insights into the functions of NK-lysin peptides in teleosts and show the potential of using NKLj27 in aquaculture for bacterial disease control.

Domoic acid (DA) is a naturally occurring amino acid structurally analogous to kainic acid (KA). DA, a neurotoxin commonly associated with toxigenic Pseudo-nitzschia species, enters the food chain via filter feeders and poses a potential threat to predators such as sea stars. To assess the presence of DA, wild-collected sea stars (Pisaster ochraceus and Asterias spp.) were analyzed for DA. Although there were no signs of a recent Pseudo-nitzschia bloom prior to collection, both species had low levels of detectable DA, primarily concentrated in the pyloric caeca. DA concentrations in P. ochraceus tissues ranged from 0 to 1033 ng g-1 tissue, averaging (±SE) 614 ± 93 ng g-1 in pyloric caeca, and were negatively correlated with body mass. DA concentrations in Asterias spp. averaged 123 ± 34 ng g-1 in pyloric caeca. Subsequently, to assess neurotoxic impacts-behaviorally and physiologically-we challenged Asterias spp. with KA, as a stand-in for DA, using intraperitoneal injections of 0, 3, or 30 μg KA g-1 body mass. Immediately following exposure, 11 out of 12 sea stars injected with 30 μg KA g-1 failed to right themselves within 30 min and their arm circumference was reduced by 19.7 ± 3.5%. Righting time, but not arm circumference, recovered within 2 d. We hypothesize that these responses precipitated from KA binding to glutamate receptors in the mutable collagenous tissue. These findings reveal that DA accumulates in sea star tissues, and that KA can cause significant yet reversible behavioral changes, raising concerns about the impact of repeated, long-term, or higher-dose exposures of wild sea stars to these neurotoxins.

Erysipelas, an infection caused by Erysipelothrix rhusiopathiae, has always been a threat to marine mammal collections. A first global survey (1989-2000) about erysipelas occurrences, covering 1384 animals, reported 69 cases of erysipelas (5%). To better understand the disease epidemiology and vaccine-related reactions, a second survey (2001-2020) was conducted, reaching a 68.6% response rate (140/204 facilities) and including 2267 cetaceans. It reported 108 cases (4.8%), with more than 5 cases annually and a 50% fatality rate. At least 1 case was reported in 40% of responding facilities, all involving non-vaccinated animals or those vaccinated only once or twice. Most facilities began vaccinating after experiencing a case, while fear of adverse fatal anaphylaxis reaction remains the primary reason for avoiding it. Notably, only 1 fatal vaccine reaction was reported in 1989, though procaine penicillin had been co-administered. Adverse reactions were rare and mostly resembled expected inflammatory reactions post vaccination such as anorexia, local swelling or blood changes. These were more frequent with oil-adjuvanted vaccines containing alpha-tocopherol or Amphigen®, and minimal to absent with aluminum hydroxide-based vaccines. Three facilities using the Amphigen®-adjuvanted ER Bac® Plus vaccine (Zoetis) observed transient lethargy and irregular breathing in 8 animals after several vaccinations, of which 1 had been treated. Regional differences in vaccine availability were observed. This 30 yr retrospective study highlights that cetaceans in human care face a greater risk of dying from erysipelas than from vaccine side effects. Furthermore, regular vaccination appears to offer effective protection against this preventable disease.

Black abalone Haliotis cracherodii from California, USA, and Baja California, Mexico, have faced massive population declines for more than 30 yr. The main factors contributing to these declines have been overfishing, pollution, climate change, and lethal diseases, such as withering syndrome, caused by the intracellular bacterium Candidatus Xenohaliotis californiensis (CXc). In recent years, the presence of an associated bacteriophage, pCXc, infecting CXc was detected and reported in some abalone species from California and Baja California. In the present study, 199 black abalone fecal samples from 14 sites along the Baja California coast were analyzed for the presence of CXc and pCXc DNA. The overall prevalence of bacteria and phage-infected bacteria was 44 and 38%, respectively. We found significant differences in the relationship between the prevalence and the mean lengths of abalone throughout the study area. This result is probably due to differences in the size-frequency distribution between sampling zones. The only site where we found a relationship between prevalence and length was in Isla Todos Santos. We did not see a relationship between abalone density and the prevalence of the bacteria and the phage. Additionally, we found a positive but non-significant correlation in prevalence between CXc and pCXc. This study is the first to detect the presence of pCXc DNA in wild populations of black abalone of Baja California.

Pathogens use host resources for replication. Consequently, pathogen traits, such as where they infect a host, might allow pathogens to capitalize on host-consumed nutrients before the host. For instance, parasites with short generation times in the host gut or blood might benefit more from host-consumed resources than the host, whereas parasites in or on the host integument (e.g. skin, cuticle, exoskeleton), such as ectoparasites, might benefit less from host-consumed resources than the host. Thus, it is unclear whether increased food consumption by hosts should reduce or amplify pathogen levels. We conducted experiments on Cuban treefrogs Osteopilus septentrionalis to test how food availability affects infection levels of ranavirus and the fungal pathogen Batrachochytrium dendrobatidis (Bd), which are both associated with mass die-offs of amphibians. Given that ranavirus is an endoparasite with a much shorter generation time than the skin-infecting Bd, we postulated that ranavirus might be able to capitalize on host-consumed resources more quickly than Bd. Hence, we hypothesized that increased food availability to hosts might reduce Bd infections more than ranavirus infections. As predicted, augmenting food access decreased Bd infection intensity but increased ranavirus infection intensity. Future work should assess whether pathogen traits, such as generation time and where they infect hosts, generally affect whether food resources more positively benefit hosts or pathogens.

A total of 4193 specimens with everted tentacles of the trypanorhynch cestode Mixonybelinia lepturi obtained from Gempylus serpens and Trichiurus lepturus were examined in order to identify abnormalities in hook shape and armature pattern. The abnormality rate of the tentacular hooks and armature was 0.09%, ranging from changed hook direction and slight changes of single hook shapes to completely altered hooks and armature patterns. In a single case, the armature pattern could not be assigned to any existing trypanorhynch family. The observed malformations were classified in 5 categories and 9 types, a categorization also to be used as a standard for other trypanorhynchs. The low abnormality rate demonstrates high reliability of tentacular hooks and armature patterns as taxonomic characters in trypanorhynch systematics, confirming that trypanorhynch larvae have identical tentacular armatures compared with their adults. Considering the low rate of abnormality, the role of environmental factors in causing the unsymmetrical changes on originally symmetrical tentacles is probably weak. Therefore, a genetic origin seems to be more probable. Such phenotypic armature variations may cause transfer of worms to new attachment sites within the same host or into a new host species, where new tentacular armatures with increased fitness are eventually formed by natural selection under the model of micro-allopatric speciation. The finding of an abnormal tentacle that unites hollow and solid hooks together with completely altered hook shapes and armature patterns is good evidence in demonstrating the ancient origin of different hook shapes and the evolutionary changes of armature patterns.

Erysipelothrix is a genus of opportunistic bacteria of humans and animals. In 2019, a marked increase in infections by the zoonotic bacterium Erysipelothrix in Cook Inlet (Alaska, USA) beluga whales Delphinapterus leucas (CIBs) was detected through routine surveillance. A retrospective study was performed using archival records from 1998 to the present; archived samples from 2006 to the present; colleague interviews; and a literature review. Erysipelothrix was detected in 18 of 63 (28.6%) CIBs necropsied between 2006 and 2023, and when present after 2017, it was the primary cause of death. Erysipelothrix was rarely detected in other species of wildlife, domestic animals or in the environment in and around Cook Inlet during the same period. Sequencing of isolates demonstrated several different lineages, negating the possibility of infection from a common source or single strain. The lack of documented previous occurrence of Erysipelothrix in or near Cook Inlet indicates that this is likely an emerging phenomenon.

The Franciscana dolphin Pontoporia blainvillei is one of the most endangered cetaceans in the South Atlantic Ocean, primarily threatened due to bycatch. Knowledge regarding the natural causes of mortality and morbidity in this species is still limited. An adult female P. blainvillei that died as a result of bycatch was found stranded on the north coast of São Paulo, Brazil. At necropsy, a multi-cavitary tumor (~10.8 × 10.1 cm, 431 g) was found on the left adrenal gland, and on cut section, the tumor was hemorrhagic and necrotic. On histopathology, the tumor presented anaplastic characteristics including moderate anisocytosis and anisokaryosis, homogeneous and finely stippled chromatin, and nucleoli sometimes evident. Occasional binucleations and atypical giant cells were observed. The tumor was immunoreactive for chromogranin A and negative/not immunoreactive for Factor VIII, CD31, pan-cytokeratin AE1/AE3, vimentin, CD56, and synaptophysin, suggesting a poorly differentiated neuroendocrine tumor (NET). A moderate deviation of the lumbar spine (lordosis), lumbar ankylosing spondylosis, and thoracolumbar and caudal spine discopathy were confirmed via post-mortem radiographs. The vertebral anomalies and NET contribute to the knowledge of natural diseases of this endangered dolphin species.

Nutritional steatitis (yellow fat disease) caused by vitamin E (vitE) deficiency is typically associated with diets high in unsaturated fatty acids or/and low levels of vitE. This work describes, for the first time, an outbreak of nutritional steatitis in cultured silver catfish Rhamdia quelen in Argentina. Necropsy, histopathology, bacteriology and molecular studies of the affected fish were performed. In addition, peroxide level and vitE concentration of the fish feed were measured. Affected specimens had firm, yellowish-brown dermo-hypodermal nodules located in the adipose fin and dorsal region of the body. Histologically, lesions consisted of fat necrosis and multifocal granulomatous lobular steatitis, primarily affecting the subcutaneous and intermuscular adipose tissue, and occasionally, the coelomic fat. Feed analyses revealed a high peroxide value (41.2 mEq kg-1), indicative of rancid feed, and a low concentration of vitE (2.7 IU kg-1). In this case, fish had been fed rancid food with an inadequate value of vitE, leading to the development of nutritional steatitis caused by vitE deficiency.

Bonamiasis, caused by haplosporidian parasites Bonamia spp., is an infectious disease prevalent in 'flat' oysters internationally. Bonamia was first detected in Australian native oysters Ostrea angasi in Victorian waters in the early 1990s and caused mass mortalities in this pilot industry. The species identity of Bonamia at that time was unclear and no attempts were made to unequivocally resolve it. Interest in O. angasi culture was renewed in 2010 alongside a small-scale bonamiasis surveillance programme, given previous experience with the parasite. Basic data on culture methods, epidemiology and pathology are presented from 2011 until the epizootic that destroyed most of the stock at the major aquaculture site in 2015. At that time, a comprehensive phylogenetic analysis of the relationship between the cause of this epizootic and other Bonamia spp. internationally demonstrated >98% homology to B. exitiosa. Moreover, the report on Perkinsus olseni is the first in O. angasi. The presumed incidental finding of the more recently identified P. beihaiensis is the first for any mollusc species in Australia.