Diseases of aquatic organisms最新文献

Nutrient deficiency can cause increased susceptibility to infectious diseases in fish, thus leading to high rates of morbidity and mortality. Thiamine deficiency complex (TDC) in fish can lead to low reproductive success and high mortality rates. Columnaris disease in salmonids, caused by Flavobacterium columnare, has resulted in devastating losses in aquaculture production and wild populations of Pacific salmon particularly associated with climate change and high water temperatures. There is growing awareness that both TDC and columnaris are emerging diseases of salmonids on the west coast of North America; however, it is unknown whether fish that survive from low/intermediate thiamine level eggs will experience latent mortality due to susceptibility to infectious diseases like columnaris. To investigate the interaction of TDC survivors and columnaris, Chinook salmon Oncorhynchus tshawytscha fry reared from either thiamine-deficient (n = 120) or thiamine-replete (n = 120) eggs were challenged with F. columnare using an immersion challenge model of infection, and morbidity/mortality, immune responses, and bacterial load were evaluated. The cumulative mortalities between the treatment groups were significantly different, with the thiamine-deficient, F. columnare-exposed fry ending the challenge with an 80.3% survival rate and the thiamine-replete, F. columnare-exposed fry ending with a 29.03% survival rate (p < 0.0001). Different transcript abundance was detected in gills and spleen of thiamine-deficient and thiamine-replete fry exposed to F. columnare. This study demonstrated that fry reared from eggs low in thiamine have an altered immune response and warrants further studies to better understand interaction with potential pathogens at different life stages.

The amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd) has devastated global amphibian biodiversity. Non-amphibian hosts might facilitate Bd spread across the landscape, but our understanding of their role remains severely limited. Several species of invertebrates have been implicated to varying degrees as potential carriers of Bd, but research is needed to understand the impact these invertebrates have on the spread and maintenance of this pathogen in the wild. Detecting Bd presence in field-collected invertebrates is a necessary first step for identifying potential vectors, but methodological comparisons have not been conducted. Detection thresholds of DNA extraction methods for Bd detection from amphibian skin swabs may not be applicable for invertebrate samples, because they may contain lower Bd loads and higher amounts of PCR-inhibitory substances. This study aimed to identify the most cost-effective and reliable method of DNA extraction for detecting Bd DNA in invertebrate samples using qPCR. We compared the effectiveness of 5 commonly used DNA extraction kits (QIAGEN, Zymo, SPINeasy, PrepMan Ultra, and Chelex resin) for Bd detection in homogenised cricket samples spiked with known concentrations of Bd. We found PrepMan Ultra to be the optimal extraction kit for a broad screening of field-collected invertebrate samples, due to its relatively low cost and the ability to detect Bd presence in homogenised cricket samples containing at least 100 zoospore equivalents. However, researchers need to conduct their own cost-benefit analysis when choosing an extraction method to ensure that the method suits their needs.

African freshwaters are inhabited by many endemic fishes. However, little is known about the associated myxozoan diversity. The present paper describes a new parasite species of Henneguya Thélohan, 1892 infecting Distichodus mossambicus Peters, 1852, an endemic freshwater fish species commonly found in the Congo Basin. Fish were collected from the Kadey River at Mindourou, a village in the East Region of Cameroon. To study the new Henneguya species, morphological analysis using light microscopy was combined with a phylogenetic analysis of small subunit ribosomal DNA (SSU rDNA) using maximum likelihood and Bayesian inference methods. White and elongated plasmodia were found in the gill lamellae. The myxospore body was 11.5 ± 0.2 (mean ± SD) (range: 10.4-12.7) µm long, 3.3 ± 0.1 (2.7-3.9) µm wide, and 2.3 ± 0.1 (1.9-2.9) µm thick. The caudal appendages were 22.1 ± 0.4 (20.1-25.9) µm long and the total length of the new species was 29.7 ± 0.3 (27.5-32.3) µm. The 2 pyriform polar capsules were of the same size, 3.7 ± 0.1 (3.2-4.2) µm long and 1.0 ± 0.03 (0.9-1.2) µm wide. Phylogeny of the SSU rDNA showed the new Henneguya species within a subclade composed exclusively of unidentified Myxobolidae infecting African Citharinoidei fish. Further work characterizing myxozoan species using both morphological, molecular, and phylogenetic data is required to better understand myxozoan diversity in Africa.

Judicious use of antimicrobials in aquaculture requires reliable antimicrobial susceptibility testing (AST) of bacterial pathogens for resistance surveillance and for advising therapy decisions. To improve AST of aquatic bacterial pathogens such as Vibrio harveyi, the Clinical and Laboratory Standards Institute (CLSI) has standardized methods specific to testing isolates collected from fish and other aquatic animals. However, no criteria, called epidemiological cutoff values (ECVs), exist yet to interpret results when testing V. harveyi with these standard methods. Microbiologists use ECVs to determine whether an isolate has decreased susceptibility to an antimicrobial relative to other isolates of the same bacterium. In this study, we generated minimal inhibitory concentration (MIC) data using 3 independent laboratories that tested 76 isolates with the CLSI standard broth microdilution method at 28°C for 24-28 h against 9 antimicrobials. The resulting MIC data for 6 of the antimicrobials listed below was combined with previously published data (Smith et al. 2023; Dis Aquat Org 155:35-42) and analyzed with the programs Normalized Resistance Interpretation (NRI) and ECOFFinder to calculate potential ECVs. In collaboration with CLSI's Working Group on Aquatic Animals, the potential ECVs were proposed to CLSI's Subcommittee on Veterinary Antimicrobial Susceptibility Testing, which voted to accept the values. These new ECVs will be included in the next edition of the VET04 supplement. The approved ECVs for enrofloxacin, florfenicol, gentamicin, oxolinic acid, oxytetracycline, and trimethoprim/sulfamethoxazole are ≤1, ≤2, ≤4, ≤1, ≤1, and ≤0.5/9.5 µg ml-1, respectively. These new interpretive criteria will improve international harmonization regarding monitoring efforts on antimicrobial susceptibility of V. harveyi.

Grey seal Halichoerus grypus populations are increasing across the North Atlantic, where occasional reports describe attacks, predation on other marine mammals and even cannibalism of their own young. Here we report injuries potentially consistent with grey seal-inflicted lesions on 4 delphinids from northwest European coastlines: 1 bottlenose dolphin Tursiops truncatus, 1 common dolphin Delphinus delphis and 2 white-beaked dolphins Lagenorhynchus albirostris. These delphinids exhibited injuries such as puncture wounds and parallel scratches, with varying degrees of tissue remodelling. This indicates that the wounds were not recent but likely occurred days to weeks before death, suggesting opportunistic interactions rather than predation. Ultimately, all 4 delphinids were believed to have died from bacterial infections, including Brucella ceti and Morganella morganii, and it is likely that these delphinids were already debilitated at the time of the seal encounters. In addition, in 2 cases, seal-associated pathogens-Streptococcus phocae and Atopobacter phocae-were isolated. This study expands the known scope of grey seal interactions to include odontocetes beyond harbour porpoises Phocoena phocoena, highlighting their potential as opportunistic or exploratory top predators. As grey seal populations increase, their interactions with cetaceans may influence individual health and broader ecosystem dynamics. Retrospective and prospective research into marine predator-prey relationships will enhance our understanding of these complex behaviours and their impact on marine ecosystems.

Yersinia ruckeri is a Gram-negative bacterium that causes enteric redmouth disease. It commonly infects farmed salmonid fishes, often requiring antimicrobial treatment. Studies on antimicrobial susceptibility patterns of Y. ruckeri have found isolates with decreased susceptibility but have lacked internationally harmonized criteria, known as epidemiological cutoff values (ECVs), which provide consensus on identifying antimicrobial resistance. To address this need, we gathered minimal inhibitory concentration (MIC) testing data for 9 antimicrobials, generated at 22°C for 24-28 and/or 44-48 h using the standard broth microdilution testing method published by the Clinical and Laboratory Standards Institute (CLSI). The dataset includes MIC data from up to 431 isolates from 7 independent laboratories. Data for each antimicrobial were analyzed with the programs Normalized Resistance Interpretation (NRI) and ECOFFinder to compare the means and standard deviations for the 2 timepoints, and to calculate wild-type cutoff values. The parameters for the timepoints were very similar, which confirmed cutoffs were only needed for the 24-28 h incubation. The cutoff values for 8 of the 9 antimicrobials are potential ECVs that have been proposed to CLSI's Subcommittee on Veterinary Antimicrobial Susceptibility Testing. Calculated cutoffs for the final antimicrobial, erythromycin, were off-scale because the MIC values clustered at higher drug concentrations. The resulting new ECVs will be included in the next edition of the VET04 supplement, which will help clinicians and researchers advance antimicrobial resistance surveillance of this bacterium.

The microsporidium Ecytonucleospora hepatopenaei (EHP) continues to disrupt farmed shrimp production globally by causing growth retardation, chronic mortality, and enhancing susceptibility to other diseases. While the susceptibility of black tiger shrimp Penaeus monodon and Pacific white shrimp P. vannamei to EHP is well known, the susceptibility of Pacific blue shrimp P. stylirostris to EHP has not been demonstrated. To determine the susceptibility of P. stylirostris to EHP, infectious inoculum was directly injected into the hepatopancreas of specific-pathogen-free (SPF) P. stylirostris. At 17 d post-injection, the developmental stages of the parasite were observed in the EHP-injected P. stylirostris, and EHP was detected by real-time PCR. The EHP-injected P. stylirostris were then divided into 2 groups. In the first group, P. stylirostris (n = 9) were cohabitated with SPF P. vannamei (n = 55), and in the second group, the hepatopancreas was excised from EHP-injected P. stylirostris, homogenized, and fed to SPF P. vannamei (n = 12). Both experimental challenge routes led to the horizontal transmission of EHP from P. stylirostris to P. vannamei, but cohabitation resulted in a stronger infection. In a follow-up study, one group of SPF P. stylirostris was fed EHP-infected P. vannamei tissue, and another group cohabitated with EHP-infected P. vannamei. Both groups of P. stylirostris developed EHP infections. These results clearly provide evidence of both P. stylirostris susceptibility to EHP and the transmission potential of EHP between P. stylirostris and P. vannamei via natural routes such as cohabitation and cannibalism.

A new myxozoan species, Henneguya dugarovi sp. nov., was observed in the gills of Amur common carp Cyprinus carpio haematopterus Martens, 1846 (subspecies of common carp), which inhabits the Lake Baikal basin. The parasite was studied on the basis of spore morphology and molecular methods. Cysts were located intralamellarly in the secondary lamellae. Mature spores of H. dugarovi sp. nov. are symmetrical, with 2 unequal caudal appendages, the spore body is obovate in frontal view and lemon-shaped in lateral view. The spores have a total length of 24-42 μm, a mean ± SD body length of 11.7 ± 0.8 μm (range 10.0-13.1 μm), a width of 8.8 ± 0.5 (7.8-10.2) μm and thickness of 7.3 ± 0.5 (5.8-8.0) μm. Two equal polar capsules are pear-shaped, blunt at the posterior end, narrowed anteriorly and widely spaced, 5.3 ± 0.4 (4.4-6.0) μm long and 3.1 ± 0.3 (2.4-4.0) μm wide. Polar tubules are coiled in 7 turns. The infection rate of H. dugarovi sp. nov. was 56%. Phylogenetic analyses showed that this species is grouped with myxosporeans infecting common carp.

This study explores the phenotypic, genotypic, and serological differences among Edwardsiella ictaluri isolated from farm-raised catfish Ictalurus spp. and ornamental fish (Danio spp. and Puntius tetrazona) in the USA. Plasmid analyses revealed diverse plasmid profiles, with varied antimicrobial resistance genes indicating diverse resistance and virulence mechanisms. Analysis of complete genome sequences revealed multiple virulence factors, including the Type III and Type VI secretion systems, with varied presence between the catfish and ornamental derived strains. Molecular analyses, including multi locus sequence analysis (MLSA) and repetitive extragenic palindromic-PCR, identified discrete genotypic differences, identifying an optimally informative MLSA scheme for demonstrating intraspecific relationships among E. ictaluri conspecifics. Serological assessments revealed marked differences between catfish and ornamental isolates, indicating distinct antigenic profiles and suggesting that E. ictaluri vaccines derived from catfish isolates may have limited efficacy against ornamental isolates, supporting anecdotal reports from the industry. This research advances our understanding of this important bacterial fish pathogen, laying a foundation to help guide approaches in vaccine design and disease mitigation in catfish and ornamental fish moving forward.

Lactococcus garvieae causes lactococcosis in several marine-cultured fish species in Japan. A new L. garvieae serotype III was recently identified in diseased striped jack Pseudocaranx dentex, yellowtail Seriola quinqueradiata, and amberjack S. dumerili. Herein, we report the first isolation of L. garvieae serotype III isolates LC2313 and LC2323 from cage-cultured cobia Rachycentron canadum. Naturally diseased fish exhibited clinical signs of hemorrhagic eyes and a curved spine. An infectivity trial on cobia using the LC2323 isolate revealed 30% mortality by intramuscular injection at doses of 105 or 107 CFU fish-1, while 50-60% mortalities were observed by intraperitoneal injection at the same infectious doses. Both the LC2313 and LC2323 isolates caused up to 100% mortality in yellowtail and amberjack during 14 d of observation. The draft genomes of LC2313 and LC2323 were 1951432 and 1953218 bp, respectively, with G+C contents of 38.9% for both isolates. A total of 1867 coding sequences were predicted for LC2313 and 1872 for LC2323 with 12 phage-related genes each. The core-genome sequence alignment indicated a close relationship between these isolates and the recently identified L. garvieae serotype III from amberjack and striped jack. Taken together, these results demonstrate the pathogenicity of L. garvieae serotype III in susceptible fish species, highlighting the need for awareness regarding disease transmission among fish species.