Journal of fish diseases最新文献

The white spot syndrome virus (WSSV) is a major threat to shrimp farming and causes substantial economic losses in aquaculture. The VP28 envelope protein of WSSV facilitates initial systemic infection in shrimp. Although mammalian-derived antibodies are used for diagnostic tests, high costs and animal welfare concerns necessitate alternative strategies. This study produced specific yolk immunoglobulin (IgY) by immunising laying hens with the VP28 envelope protein as a cost-effective alternative for WSSV detection. IgY antibody titres and specificity were assessed using ELISA and western blotting, and their performance was compared with that of IgG rabbit antibodies. Stability was tested under various pH and salinity conditions. A time-course infectivity experiment analysed infection progression. Western blot analysis using IgY detected WSSV in shrimp samples at 6 h post-infection (h p.i.) in the haemolymph and eyestalk. By 12 h p.i., the gills, head soft tissue, appendages and other organs showed positive. Shrimp mortality occurred at 36 h p.i. Western blot findings matched those of IgG rabbit antibodies, proving that IgY antibodies were viable. Based on these findings, a validation study was conducted using 55 field samples collected from various regions of India. IgY serves as an innovative biological recognition component for early diagnosis of WSSV, offering an ethical and economical option for disease management in aquaculture.

Aeromonas hydrophila can cause disease in various aquatic animals, but there exist no effective alternatives to control its outbreak. In this study, diseased largemouth bass were collected from the breeding farm Lake Dahong (Chongqing, China), a strain SK-2 was isolated and identified as A. hydrophila. In order to investigate the pathogenicity of the strain and the protective efficacy of the inactivated vaccine, we firstly evaluated the virulence factors including hemolytic, proteolytic, and amylolytic activities. The results displayed that the diameters of hemolytic, proteolytic, and amylolytic circles reached 0.94 ± 0.10, 2.15 ± 0.16, and 1.51 ± 0.14 cm respectively. Median lethal dose (LD₅₀) was tested and the LD₅₀ value was calculated as 1.39 × 10⁵ CFU/g. Besides, a challenge test was conducted and two levels (LD₅₀ and 1/10 LD₅₀) were set for intraperitoneal injection. Significant immune responses were found in the serum and head kidney samples, with the higher superoxide dismutase (SOD), peroxidase (POD) and malondialdehyde (MDA) levels (p < 0.05). The results of qPCR revealed that tumour necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and interferon-γ (IFN-γ) expression levels were elevated in the liver and head kidney samples, reaching a stable state at 48 h. Furthermore, the inactivated vaccine of SK-2 was prepared using formalin and 0.85% saline (CG) and the inactivated vaccine of SK-2 (AHIV) was intraperitoneally injected for 28-d immunisation. The results indicated the SOD and lysozyme (LZM) activities in the serum of the AHIV group were dramatically higher (p < 0.05) than those in the CG group, the catalase (CAT) and MDA levels were remarkably increased (p < 0.05) compared with the CG group, and these immune-related genes exhibited conspicuous upregulation (p < 0.05), suggesting the inactivated vaccine of SK-2 could bring about subdued oxidative stress in the innate immunity of largemouth bass. The wide-type SK-2 was challenged into the largemouth bass post 28-d immunisation, and the relative protection was calculated as 86.21%. These findings provide theoretical support for the bacterial disease control of largemouth bass.

A previous study in our laboratory revealed that microRNA-33 (miR-33) regulated autophagy initiation and inflammatory response by targeting Atg5; furthermore, in this study, chloroquine (CQ), lipopolysaccharide (LPS) and the miR-33 inhibitor were transfected into Ctenopharyngodon idella kidney (CIK) cells to explore whether miR-33 regulated late-stage autophagy and inflammatory response induced by LPS. The results showed that CQ inhibited the fusion of autophagosome and lysosome and significantly increased the secretion of pro-inflammatory cytokines (p < 0.05). Interestingly, miR-33 was also significantly upregulated after CQ incubation (p < 0.05). However, compared with the CQ group, the expression of beclin-1, atg5, atg7 and atg12 did not recover after inhibiting miR-33 (p > 0.05). But the expression of tnf-α, il-6, il-1β, il-8 and nf-κb, as well as the secretion of TNF-α, IL-6, IL-12 and IL-1β, were significantly downregulated, and the activities of ALP, SOD and CAT were significantly increased (p < 0.05). Furthermore, CIK cells were treated with LPS to construct an inflammation model, and miR-33 expression was significantly upregulated (p < 0.05). In contrast, the miR-33 inhibitor reversed the effects of LPS by decreasing the transcription levels of tnf-α, il-6, il-1β, il-8 and nf-κb; inhibiting the secretion of TNF-α, IL-6, IL-12 and IL-1β; and increasing the activities of ACP, ALP, SOD and CAT (p < 0.05). Taken together, the inhibition of miR-33 alleviated inflammatory response in CIK cells induced by CQ and LPS, but miR-33 regulated autophagy independently of CQ. These findings provided a theoretical foundation and a novel perspective for further understanding the mechanisms by which miR-33 regulated autophagy and inflammation in fish.

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.