Journal of fish diseases最新文献

Piscirickettsiosis is a systemic infectious disease caused by Piscirickettsia salmonis, a Gram-negative, biofilm-forming bacterium capable of infecting the main salmonid species farmed in Chile. The initial stages of P. salmonis infection occur in the mucous membranes of the skin, gills, and intestine before spreading systemically. At the intestinal level, several pathogenic bacteria can disrupt the functionality of the epithelial barrier as an infection mechanism, associated with alterations in the expression of immune genes and intercellular junctions. The aim of this study was to determine in vitro the effect of P. salmonis infection in both sessile and planktonic conditions on the morpho functionality of the intestinal epithelial cell line RTgutGC of rainbow trout. Thus, the effect of P. salmonis infection on immune gene expression and intercellular junctions was evaluated using RT-qPCR, intercellular junction protein levels via Western blot, transepithelial resistance (TEER) modulation, cytotoxicity, and ZO-1 localization through immunofluorescence. The results indicate that P. salmonis LF-89 and EM-90 in both sessile and planktonic conditions significantly modulate the expression of il-8, il-1β, tgf-β, and zo-1, claudin-3, and E-cadherin. Interestingly, alterations in the levels of Claudin-3 and E-cadherin, associated with the altered immunolocalization of ZO-1 after the infection with P. salmonis, were detected. Importantly, an increase in bacterial translocation associated with a decrease in the TEER value, from the first 12 h post-infection, was measured. These findings suggest that P. salmonis modulates the expression of genes and proteins related to intercellular junctions, modifying the epithelial morpho-functionality, which could allow bacterial translocation in the early stages of infection.

Nocardia seriolae is a causative agent for fish skin ulcers and sarcoidosis, resulting in significant losses in both brackish and freshwater fish farming industries. From October to November 2023, channel catfishes (Ictalurus punctatus) cultured in Xiaowan reservoir at Dali city, Yunnan province in China, showed gross pathological changes with skin ulcers, white nodules in the liver and heart, histopathological tests revealed the typical granulomas and chronic hepatitis changes in the liver, and the clumps of filamentous bacteria in the heart and spleen. A Gram-positive acid-fast bacterium (CCF_NS01) was isolated from viscera (liver, spleen and kidney); biochemical tests and 16sRNA-GyrB gene concatenated sequences analysis of this isolated microorganism identified it as N. seriolae. Drug sensitivity testing indicated susceptibility to commonly used antibiotics such as co-trimoxazole, doxycycline, enrofloxacin, florfenicol, amikacin and rifampicin. In isolated CCF_NS01, multiple pathogenic factors corresponding to encoding genes were detected, including espG, mftF, pcaA, fadD32, pks13, narJ, feoB, sodA, katG and mceF. 100% mortality with 1 × 10⁸, 1 × 10⁷ and 1 × 10⁶ cfu/mL in a 35-d challenge test period was observed, and the intraperitoneal injection median lethal dose (LD₅₀) was 1.89 × 10⁴ cfu/mL. This is the first isolation report of N. seriolae infection from cultured channel catfish, aiming to warn against the continuous host-range expansion of this pathogen, which is threatening the inland aquaculture industry.

Freshwater is a non-pharmaceutical tool used for the control of Caligus infestation with a proven effect on adult and larval stages. However, the minimum exposure time to achieve a greater effect (100%) on juvenile stages has not been determined through in vivo tests. Therefore, it is important to determine these minimum times on C. rogercresseyi chalimus, considering that freshwater baths should be performed with a wellboat to achieve the greatest effect. A study was thus formulated that allowed us to evaluate the effect of applying freshwater treatment on C. rogercresseyi juveniles at different exposure times through in vivo tests on Atlantic salmon (Salmo salar). The results indicated that a treatment of more than 2.5 h with freshwater induces a greater effect (100%) and mortality (~95%) on juvenile stages, at least at chalimus III-IV. Juvenile stages are a critical point in population dynamics and control of the parasite, since those that survive treatment increase the possibility of augments in parasitic loads in the short term, and cause loss of sensitivity. Based on these results, freshwater treatment exposure time should exceed 2.5 h in order to ensure effectiveness on parasite stages and, therefore, to avoid development of resistance to freshwater and prolong the useful life of this non-pharmaceutical tool.

This study presents a comprehensive molecular and epidemiological characterisation of infectious pancreatic necrosis virus (IPNV) in Chilean salmon aquaculture. Between 2015 and 2016, 26 sampling events were conducted in freshwater and seawater farms spanning a broad latitudinal gradient (30.3° S to 52.6° S). Three diagnostic methods were used: Quantitative real-time Polymerase Chain Reaction (PCR) (qRT-PCR) (targeting VP1 and VP2 protein coding genes), nested PCR and virus isolation in CHSE-214 cells. In addition, a 523-bp VP2 gene fragment was sequenced directly from samples. These approaches were employed to assess detection sensitivity and to explore IPNV genogroup distribution and persistence. Nested PCR and viral isolation detected IPNV in 50 of 53 samples, outperforming qRT-PCR, which detected only 39. Phylogenetic analysis of the 523-bp VP2 gene fragment classified the isolates into two genogroups—5 (Salmo salar) and 1 (Oncorhynchus spp.), confirming host-specific associations. Identical or near-identical sequences were identified in geographically distant farms and temporally spaced samples, suggesting persistent isolates and potential long-distance spread, likely via egg transfers or fish movement. The most severe mortality event (> 125,000 fish) occurred during a genogroup 1 outbreak (Isla del Rey, GMTS, O. kisutch), followed by genogroup 5 outbreaks documented in Molco Alto (PMLC, S. salar) and Chayahue (S. salar). Although less frequently detected, genogroup 1 was associated with higher virulence, particularly in coho salmon. These findings highlight the need of integrated diagnostic strategies, genogroup-specific monitoring and strengthened biosecurity to mitigate the impact of IPNV in Chilean salmon farming.

Lactococcus petauri is an emerging bacterial pathogen associated with disease outbreaks in freshwater and marine fish species worldwide. While it has been increasingly reported in countries bordering the Mediterranean Sea, no official records of L. petauri have yet been made in Italy for saltwater species. This study reports, for the first time, the presence of L. petauri in European seabass (Dicentrarchus labrax) farmed in land-based tanks along the south-western coast of Italy, based on a retrospective analysis of previously isolated strains. Although only a single isolate was positive, the finding is of notable significance as it originated from a sample collected in 2012. This temporal aspect highlights the likelihood that L. petauri has been circulating in Italian aquaculture systems for at least a decade. The isolate also exhibited a broad antimicrobial resistance profile, including resistance to amoxicillin, fluoroquinolones and trimethoprim/sulfamethoxazole. The historical misidentification of L. petauri is linked to its clinical similarity with Lactococcus garvieae. This highlights the value of re-analysing archived strains with modern tools and underlines the need for accurate diagnostics in aquaculture. The detection in D. labrax extends the known host range and suggests a longer, undetected presence in the Mediterranean.

Gut bacterial communities play a key role in shrimp health; thus, their modulation has been a target of dietary supplements which also function in enhancing disease and stress resistance of shrimp. However, this also raised the question of whether immunostimulants yield distinct changes in the gut bacterial composition or whether there are consistent features across all treatments. Here, we performed a machine learning-aided meta-analysis of 16S rRNA gut bacterial community studies of immunostimulants for Penaeus vannamei. Sequence reads from the selected studies were obtained and processed through bioinformatics tools. While beta diversity analysis suggests similarities between the normal, infected and stimulated shrimp, alpha diversity indices showed higher species richness in the gut bacterial communities of shrimp fed with immunostimulants. Specific beneficial taxa were enriched upon immunostimulation, while potentially pathogenic taxa decreased in abundance. Random forest modelling also identified key predictor taxa which may be used to classify gut bacterial communities based on immune status, type of immunostimulant and the specific immunostimulant. Despite some shared patterns in differential abundance—having decreased relative abundances of Photobacterium and other members of Gammaproteobacteria—the influence of immunostimulation on gut bacterial community composition was type- and treatment-specific, as evident in the distinct abundance profiles of the predictor taxa. Functional prediction analysis also showed distinct pathways enriched in immunostimulated shrimp, as influenced by the type of the immunostimulant. This study highlighted the specific impacts of dietary supplementation-induced immunostimulation on gut bacterial communities and identified key features in immunostimulated shrimp which provide a novel perspective on the interplay between gut bacterial community and immunity.