Journal of fish diseases最新文献

Decapod iridescent virus 1 (DIV1) causes severe disease outbreaks in shrimp and crab culture areas. A simple, rapid, and visual DIV1 assay is important for the control of viral diseases. This study presented a novel DIV1 detection method that combines recombinase polymerase amplification (RPA) and lateral flow strip (LFS). After selecting primers and probes, we optimised the concentration of the reverse primers, reaction time, as well as reaction temperature of RPA-LFS detection. RPA can amplify the target gene within 18 min at a constant temperature of 38°C, and LFS can observe the amplification results within 3 min. Importantly, there is no cross-reactivity with other infectable shrimp viruses and pathogens, such as WSSV, IHHNV, TSV, EHP, CMNV, YHV, MrNV samples, as well as Vp_AHPND. In addition, RPA-LFS has high detection sensitivity, with a lower detection limit of 1.12 × 10¹ copies/μL. Using 110 field samples, the results of qPCR recommended by WOAH (OIE) and RPA-LFS were identical, indicating that RPA-LFS is as reliable as qPCR. The RPA-LFS assay is a valuable tool for the rapid and accurate detection of DIV1.

Infectious pancreatic necrosis virus (IPNV) can cause devastating disease in Atlantic salmon (Salmon salar). IPNV has a broad host range and may threaten other aquaculture species. Understanding interspecies transmission of IPNV is crucial for protecting the aquaculture industry. With the expansion of fish farming (in Norway), it is important to assess whether a pathogen can transmit from one fish species to another and cause disease. We investigated whether IPNV-infected Atlantic cod can shed IPNV, leading to infection in other fish important to Norwegian aquaculture: halibut, salmon and lumpfish, using the cohabitation experimental trial method. Virus shedding, transmission, fish mortality and pathology were assessed. We documented virus shedding in water and mortality in IPNV-injected Atlantic cod. No mortality was observed in the cohabitated fish species during the experimental period. We confirmed lesions consistent with IPN by histopathology and immunohistochemistry in IPNV-injected Atlantic cod and in IPNV-PCR positive cohabitant Atlantic halibut. Cohabitant Atlantic cod, Atlantic salmon, Atlantic halibut and lumpfish were also found positive for IPNV by PCR, suggesting that IPNV-infected Atlantic cod can transfer infection to other farmed fish species. These findings highlight the potential risk of pathogen spread among farmed fish species and demonstrate the importance of understanding infectious fish disease epidemiology.

This study reports the first confirmed case of Myxobolus koi parasitic infection in koi (Cyprinus carpio koi) imported into Thailand. Infected fish exhibit clinical signs during the quarantine process, including lethargy, tachypnea, flared gill opercula and excessive mucus production in the gills. The gross pathological findings included swollen and pale gills interspersed with white nodules. Microscopic examination of gill biopsies revealed mucus clumps and numerous pyriform myxospores, with no evidence of other parasites. Molecular analysis confirmed the presence of Myxobolus spp. DNA through PCR amplification targeting the 18S SSU rRNA. Phylogenetic analysis of 776 bp sequences from our representative isolates (CU01, CU02 and CU03) revealed 100% nucleotide identity with M. koi sequences from goldfish in China (OM757920) and koi in the USA (FJ841887), which formed a distinct clade with strong bootstrap support. Haematological parameters were compared between infected and healthy fish from the same batch, revealing significantly elevated levels of creatine and ALT (p < 0.05) in the infected group. Histopathological examination revealed severe gill damage, with plasmodia infiltrating and disrupting the lamellar architecture. The well-delineated pink fibrous septa encapsulated mature myxospores and pansporoblasts. Scanning and transmission electron microscopy revealed that the M. koi spores, measuring 5.2 × 2.92 μm, were oval, elongated and pyriform, with coiled polar filaments enclosed within two polar capsules. These findings document the occurrence of M. koi in Thailand, underscore its transboundary transmission via international trade and highlight the need for enhanced biosecurity measures to mitigate the spread of aquatic pathogens.

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.