Mortality from scale drop disease in farmed Lates calcarifer in Southeast Asia

jfd12915-fig-0001-m

Clinically diseased adult Lates calcarifer from a natural outbreak showing (a) fin rot and loss of scales; (b) scales along the lateral line detached easily upon gently rubbing; (c) ventral surface of some fish showing loss of scales and skin haemorrhage

Abstract

In Southeast Asia, a new disease called scale drop disease (SDD) caused by a novel Megalocytivirus (SDDV) has emerged in farmed Asian sea bass (Lates calcarifer) in Singapore, Malaysia and Indonesia. We received samples from an Eastern Thai province that also showed gross signs of SDD (loss of scales). Clinical samples of 0.2-1.1 kg L. calcarifer collected between 2016 and 2018 were examined for evidence of SDDV infection. Histopathology was similar to that in the first report of SDDV from Singapore including necrosis, inflammation and nuclear pyknosis and karyorrhexis in the multiple organs. Intracytoplasmic inclusion bodies were also observed in the muscle tissue. In a density-gradient fraction from muscle extracts, TEM revealed enveloped, hexagonal megalocytiviral-like particles (~100-180 nm). By PCR using primers derived from the Singaporean SDDV genome sequence, four different genes were amplified and sequenced from the Thai isolate revealing 98.7%-99.9% identity between the two isolates. Since viral inclusions were rarely observed, clinical signs and histopathology could not be used to easily distinguish between SDD caused by bacteria or SDDV. We therefore recommend that PCR screening be used to monitor broodstock, fry and grow-out fish to estimate the current impact of SDDV in Southeast Asia and to prevent its spread.

KEYWORDS:

Lates calcarifer ; PCR; SDDV; scale drop disease

https://onlinelibrary.wiley.com/doi/full/10.1111/jfd.12915

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Natural occurrence of edwardsiellosis caused by Edwardsiella ictaluri in farmed hybrid red tilapia (Oreochromis sp.) in Southeast Asia

Edwardsiellosis

Abstract

Infections caused by Edwardsiella ictaluri bacteria have mainly affected the catfish aquaculture industry in Asia and America, while few reports reveal E. ictaluri-associated mortality in non-catfish species. Here, we report a natural occurrence of E. ictaluri in hybrid red tilapia juveniles farmed in a floating cage system in Southeast Asia. Cumulative mortality reached 40–50% within the first month after stocking. Diseased fish exhibited the presence of numerous white spots in the swollen spleen and head kidney. Pure cultures of pinpoint bacterial colonies were recovered from internal organs of all naturally diseased fish (n = 10) and subsequently four representative isolates were chosen for further identification and analyses. The bacteria were later confirmed as E. ictaluri based on biochemical characteristics, specific PCR for both genus and species levels, partial 16S rRNA and gyrB sequencing. Artificial infections using Nile tilapia juveniles produced Edwardsiellosis with typical signs of visceral white spots as observed in naturally diseased fish. Discovery of E. ictaluri infection in farmed red tilapia adds to the growing list of emerging pathogens in tilapia aquaculture in the region of which better awareness needs to be made.

Personalized Share Link: https://authors.elsevier.com/a/1Xkv5ACeXvu6v

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TiLV histopathology

TiLV 2018

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Histopathology and culturable bacteria associated with “big belly” and “skin nodule” syndromes in ornamental Siamese fighting fish, Betta splendens

How to cite: Dong HT, Senapin S, Phiwsaiya K, Techatanakitarnan C, Dokladda K, Ruenwongsa P, Panijpan B (2018) Histopathology and culturable bacteria associated with “big belly” and “skin nodule” syndromes in ornamental Siamese fighting fish, Betta splendens. Microbial Pathogenesis. DOI: 10.1016/j.micpath.2018.06.005.

20180609_092928

Abstract

The Siamese fighting fish (Betta splendens) is one of the popular aquarium ornamental fish in the global trade. Large numbers of ornamental fish farmed in central Thailand suffered from two common syndromes; preliminarily named skin nodule syndrome (SNS) and big belly syndrome (BBS): they showed noticeable clinical signs of abnormal appearances resulting in depressed saleability. Since very few specifics are known about causative agents of these syndromes, this study aimed at investigating histopathological features and culturable bacteria associated with these fish infected in the process of farming. Histopathologically, SNS fish consistently exhibited necrosis and severe melanization in the muscles and multiple internal organs. Whereas BBS fish exhibited either typical granulomas or tissue damage associated with acid-fast stained bacteria and Gram negative bacteria, respectively. Six different Gram negative bacterial species were recovered from BBS fish while 23 bacterial species belonging to 14 genera were recovered from fish suffering from SNS. Most of the culturable bacteria are new to betta fish and some of them are known to be marine bacteria, suggesting possible entry route via a contaminated live feed, commercial Artemia shrimp. The true causative agents of these syndromes remain unclear. However, histopathological changes and existence of a wide range of bacteria associated with the naturally diseased fish suggest involvement of multiple bacterial infections.

Keywords: Betta splendens; Big belly syndrome; Culturable bacteria; Histopathology; Skin nodule syndrome

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Quinolone-resistant phenotype of Flavobacterium columnare isolates harbored point mutations in both parC and gyrA but not in either gyrB or parE

How to cite: Mata W, Putita C, Dong HT, Kayansamruaj P, Senapin S, Rodkhum C (2018) Quinolone-resistant phenotype of Flavobacterium columnare isolates harbored  point mutations in both parC and gyrA but not in either gyrB or parE. Global Antimicrobial Resistance. doi: 10.1016/j.jgar.2018.05.014

Abstract

Objective: Determination of mutations associated with quinolone-resistant (QR) phenotype of Flavobacterium columnare isolates.

Methods: The susceptibility of F. columnare isolates (n = 53) to 11 antibiotics, including 2 quinolones, was investigated using disk diffusion method. Oxolinic acid was subsequently chosen for minimum inhibitory concentration (MIC) assay. PCR and sequence analysis of four genes involved in the quinolone resistance-determining regions (QRDRs) from OA-resistant F. columnare compared to that of susceptible isolates were subsequently investigated.

Results: The result of disk diffusion assay revealed that the majority of isolates was susceptible to all tested antibiotics. However, 14 and 8 isolates were resistant to 2 quinolone antibiotics; oxolinic acid (OA) and nalidixic acid (NA), respectively. No multiple drug resistance was found in this study. MIC assay revealed 4 additional isolates that were resistant to OA (≥4 μg mL−1), making a total of 18 OA-resistant isolates obtained in this study. The results of DNA sequencing showed that missense mutations in both parC and gyrA but not in either gyrB or parE were identified in QR F. columnare isolates. Mutation in parC resulted in a change in His87-Tyr. For gyrA, 15 isolates of Thai origins exhibited change at residue 83 from Ser to either Phe, Tyr or Ala, whereas 3 Vietnamese isolates contained two mutation sites, Ser83-Ala and Asp87-Tyr.

Conclusion: This study is the first to reveal that QR phenotype of F. columnare isolates harbored missense mutations in both parC and gyrA but not in gyrB and parE of the QRDRs.

Source: https://www.sciencedirect.com/science/article/pii/S2213716518300985

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C-terminal domain of WSSV VP37 is responsible for shrimp haemocytes binding which can be inhibited by sulfated galactan

How to cite: Sotanon N, Saleeart A, Rattanarojpong T, Dong HT, Senapin S, Wongprasert K, Sarikavanij S, Khunrae P (2018) C-terminal domain of WSSV VP37 is responsible for shrimp haemocytes binding which can be inhibited by sulfated galactan. Fish and Shellfish Immunology. 77: 312-318

Abstract

Viral envelope proteins play an important role in facilitating the attachment of viruses to the surface of host cells. Here, we investigated the binding of White Spot Syndrome Virus (WSSV) VP37 to haemocytes of whiteleg shrimp, Litopenaeus vannamei. Three versions of recombinant VP37 proteins, including full length VP37 (VP37(1-281)), C-terminal domain VP37 (VP37(111-281)) and C-terminal domain disrupted VP37 (VP37(1-250)) were individually expressed and tested for their haemocytes binding ability. Through an ELISA-based binding assay, we found that VP37(111-281) bound to shrimp haemocytes in a similar way to VP37(1-281), while VP37(1-250) exhibited a significantly weaker binding. This suggests that the C-terminal domain of VP37 is required for the binding of VP37 to shrimp haemocytes. Furthermore, we found that the binding of VP37 to shrimp haemocytes was impaired by pre-incubation of VP37 with sulfated galactan (SG), a sulfated polysaccharide derived from red seaweed (Gracilaria fisheri). Previously, it has been shown that a type of sulfated polysaccharide, heparin, is also present in L. vannamei. To investigate the role of heparin as a receptor for VP37, the binding of VP37 to porcine heparin, whose structure is similar to that found in L.vannamei, was investigated in a Surface Plasmon Resonance (SPR) system. The results showed that VP37 bound strongly to heparin with binding affinity (KD) of 1.0 μM and the binding was significantly blocked by SG. These findings have lead us to propose that the attachment of WSSV might be mediated by the interaction between VP37 and a heparin-like molecule presented on the shrimp cells.

KEYWORDS:

Heparin; Shrimp; Sulfated galactan; VP37; WSSV

PMID:29601994
DOI:10.1016/j.fsi.2018.03.043
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Tilapia lake virus: a threat to the global tilapia industry?

How to Cite: Jansen MD, Dong HT, Mohan CV (2018) Tilapia lake virus: a threat to the global tilapia industry? Review in Aquaculture. https://doi.org/10.1111/raq.12254 [open access].

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Photomicrographs of haematoxylin and eosin‐stained sections of tissue from the liver, kidney and brain of normal fish (a, e, g) and TiLV‐infected fish (b–d, f, h). The infected liver tissue showed syncytial hepatocytes and foamy cytoplasm (b), intracytoplasmic inclusion bodies (c) and inflammation with pancreatic necrosis (d). Kidney tissue showed syncytial cells and severe infiltration of inflammatory lymphocytes (f). Brain tissue also showed syncytial cells and severe infiltration of inflammatory lymphocytes (h).

Abstract

Tilapia lake virus (TiLV) is a recently described virus affecting wild and farmed tilapines. At present, it has been reported on three continents (Asia, Africa and South America) and the number of countries where the agent has been detected is likely to increase rapidly as a result of increased awareness, surveillance and availability of diagnostic methods. Any lack of openness regarding the TiLV status of a translocating live tilapia population destined for aquaculture may inadvertently contribute to the spread of the agent. Currently, there is no cure for viral diseases in aquaculture and while vaccines and selective breeding have proved successful in reducing the severity of some viral diseases, there are currently severe knowledge gaps relating to TiLV and no effective, affordable vaccines are yet available. This paper summarizes the published scientific information on TiLV and highlights important issues relating to its diagnosis, mitigation and control measures. While there have been no scientific studies on the socio‐economic impact of TiLV, it may pose a significant threat particularly to small‐scale fish farmers’ livelihoods and wild tilapine populations if left uncontrolled. To aid disease investigations, the authors propose case definitions for suspected and confirmed cases of TiLV infections.

Source: https://onlinelibrary.wiley.com/doi/full/10.1111/raq.12254

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