OBJECTIVE: To evaluate the performance of recombinase-aided amplification (RAA) assay in detection of Clonorchis sinensis metacercariae in freshwater fish samples, so as to provide insights into standardization and field application of this assay. METHODS: Wild freshwater fish samples were collected in the rivers of administrative villages where C. sinensis-infected residents lived in Jiangyan District, Xinghua County and Taixing County of Taizhou City, Jiangsu Province from June to September 2022. Genomic DNA was extracted from six freshwater fish specimens (5 g each) containing 0, 1, 2, 4, 8 and 16 C. sinensis metacercariae for fluorescent RAA assay, and the diagnostic sensitivity was evaluated. Fluorescent RAA assay was performed with genomic DNA from C. sinensis, Metorchis orientalis, Haplorchis pumilio and Centrocestus formosanus metacercariae as templates to evaluate its cross-reactions. In addition, the detection of fluorescent RAA assay and direct compression method for C. sinensis metacercariae was compared in field-collected freshwater fish samples. RESULTS: Positive amplification was found in fresh-water fish specimens containing different numbers of C. sinensis metacercariae, and fluorescent RAA assay was effective to detect one C. sinensis metacercaria in 5 g freshwater fish specimens within 20 min. Fluorescent RAA assay tested negative for DNA from M. orientalis, H. pumilio and C. formosanus metacercariae. Fluorescent RAA assay and direct compression method showed 5.36% (93/1 735) and 2.88% (50/1 735) detection rates for C. sinensis metacercariae in 1 735 field-collected freshwater fish samples, with a statistically significant difference seen (χ² = 478.150, P < 0.001). There was a significant difference in the detection of C. sinensis metacercariae in different species of freshwater fish by both the direct compression method (χ² = 11.20, P < 0.05) and fluorescent RAA assay (χ² = 20.26, P < 0.001), and the detection of C. sinensis metacercariae was higher in Pseudorasbora parva than in other fish species by both the direct compression method and fluorescent RAA assay (both P values < 0.05). CONCLUSIONS Fluorescent RAA assay has a high sensitivity for detection of C. sinensis metacercariae in freshwater fish samples, and has no cross-reactions with M. orientalis, H. pumilio or C. formosanus metacercariae. Fluorescent RAA assay shows a higher accuracy for detection of C. sinensis infections in field-collected freshwater fish than the direct compression method.
Animals ; Clonorchis sinensis/genetics* ; Metacercariae/genetics* ; Recombinases ; Fresh Water ; Fishes ; DNA ; Fish Diseases/diagnosis*

Cyprinid herpesvirus 3 (CyHV-3) is the causative agent of an extremely contagious and aggressive disease afflicting common corp Cyprinus carpio L. termed koi herpesvirus disease (KHVD). Since it was first reported in 1997, the virus has spread worldwide rapidly, leading to enormous financial losses in industries based on common carp and koi carp. This review summarizes recent advances in CyHV-3 research on the etiology, epidemiology, pathogenesis, diagnosis, prevention, and control of KHVD.
Animals ; Fish Diseases ; diagnosis ; virology ; Fishes ; classification ; virology ; Herpesviridae ; genetics ; isolation & purification ; physiology ; Herpesviridae Infections ; diagnosis ; veterinary ; virology

Bacterial cold water disease, enteric red mouth disease and frunculosis are the common bacterial diseases of fish worldwide. The etiologic agents of these diseases are Flavobacterium (F.) psychrophilum, Yersinia (Y.) ruckeri and Aeromonas (A.) salmonicida subsp. salmonicida, respectively. In this study, a multiplex polymerase chain reaction (m-PCR) method with YER8/10-Fer3/4-FP1/3 primer pairs which can identify these fish pathogens simultaneously was developed and optimized. In optimized conditions, neither false specific nor nonspecific amplification occurred. The detection limits of the m-PCR method using DNA extracts from dilutions of pure cultures of bacteria were 35 pg for Y. ruckeri and F. psychrophilum and 70 pg for A. salmonicida subsp. salmonicida. It was determined that 15 CFU Y. ruckeri and F. psychrophilum and 30 CFU A. salmonicida subsp. salmonicida could be detected by m-PCR developed using genomic DNA extracted from dilutions of the suspensions. The detection limits in the presence of tissue debris were 125 CFU for Y. ruckeri and F. psychrophilum and 250 CFU for A. salmonicida subsp. salmonicida. In conclusion, we submit that the m-PCR method developed and optimized in this study can be used for accurate and rapid identification of these bacteria.
Aeromonas salmonicida/*genetics ; Animals ; DNA Primers/genetics ; Fish Diseases/*diagnosis/*microbiology ; Fishes ; Flavobacterium/*genetics ; Gram-Negative Bacterial Infections/diagnosis/*veterinary ; Polymerase Chain Reaction/methods/*veterinary ; Yersinia rucker/*genetics

A strain of grass carp reovirus was isolated from sick grass carp with symptoms of haemorrhage in Guangdong province in 2009. The strain was tentatively named as GCRV-GD108 because it was isolated from grass carp and possessed 11 segments of dsRNA. Complete genome sequence analysis showed that significant differences existed between GCRV-GD108 and GCRV, as well as other known species of aquareovirus. In this study, molecular characteristics of diseased grass carp collected from different farms in Guangdong, Fujian and Hunan provinces were assayed. Based on the sequences of the 11 segments of GCRV-GD108, PCR primers corresponding to each of the segments were designed and synthesized. Total RNA of the diseased fish was extracted and used as templates of RT-PCR reaction. Specific amplification bands were obtained from all of the samples whereas no band was produced from GCRV standard strain. While using the primers specific to GCRV produced specific band in GCRV standard strain rather than in these collected samples. Sequencing of the amplification products showed that these samples displayed high similarities with each other (95.2%-99.4%), and they also shared high sequence similarities with that of GCRV-GD108 (95.0%-99.8%), suggesting that these samples shared similar molecular characteristics with those of GCRV-GD108, and were quite different from GCRV as well as the known species of genus aquareovirus. The results indicated that there are different molecular types of reovirus existed in the pond-cultured grass carp in China, and GCRV-GD108 is a representative strain in southern China, therefore great attention should be paid in order to control the disease efficiently, especially in vaccine preparation. Two pairs of primers were chosen to establish a duplex PCR assay method by combining each pair of the primers specific to GCRV-GD108 with the GCRV primer pair respectively. The duplex PCR assay method will enable the identification of GCRV-GD108 or GCRV by only a single PCR reaction.
Animals ; Carps ; virology ; China ; Fish Diseases ; diagnosis ; virology ; Molecular Sequence Data ; Polymerase Chain Reaction ; methods ; Reoviridae ; genetics ; isolation & purification ; Reoviridae Infections ; veterinary ; virology

A multiplex PCR protocol was established to simultaneously detect major bacterial pathogens in olive flounder (Paralichthys olivaceus) including Edwardsiella (E.) tarda, Streptococcus (S.) parauberis, and S. iniae. The PCR assay was able to detect 0.01 ng of E. tarda, 0.1 ng of S. parauberis, and 1 ng of S. iniae genomic DNA. Furthermore, this technique was found to have high specificity when tested with related bacterial species. This method represents a cheaper, faster, and reliable alternative for identifying major bacterial pathogens in olive flounder, the most important farmed fish in Korea.
Animals ; Edwardsiella tarda/genetics/*isolation & purification ; Enterobacteriaceae Infections/diagnosis/microbiology/*veterinary ; Fish Diseases/*diagnosis/microbiology ; Fisheries/*methods ; *Flatfishes ; Multiplex Polymerase Chain Reaction/economics/*veterinary ; Sensitivity and Specificity ; Streptococcal Infections/diagnosis/microbiology/*veterinary ; Streptococcus/genetics/*isolation & purification

Intestinal giant-cystic disease (IGCD) of the Israel carp (Cyprinus carpio nudus) has been recognized as one of the most serious diseases afflicting inland farmed fish in the Republic of Korea, and Thelohanellus kitauei has been identified as the causative agent of the disease. Until now, studies concerning IGCD caused by T. kitauei in the Israel carp have been limited to morphological and histopathological examinations. However, these types of diagnostic examinations are relatively time-consuming, and the infection frequently cannot be detected in its early stages. In this study, we cloned the full-length 18S rRNA gene of T. kitauei isolated from diseased Israel carps, and carried out molecular identification by comparing the sequence with those of other myxosporeans. Moreover, conventional PCR and real-time quantitative PCR (qPCR) using oligonucleotide primers for the amplification of 18S rRNA gene fragment were established for further use as methods for rapid diagnosis of IGCD. Our results demonstrated that both the conventional PCR and real-time quantitative PCR systems applied herein are effective for rapid detection of T. kitauei spores in fish tissues and environmental water.
Animals ; Carps ; DNA Primers/genetics ; DNA, Ribosomal/chemistry/genetics ; Fish Diseases/*diagnosis/parasitology ; Molecular Diagnostic Techniques/*methods ; Molecular Sequence Data ; Myxozoa/genetics/*isolation & purification ; Parasitic Diseases, Animal/*diagnosis/parasitology ; RNA, Ribosomal, 18S/genetics ; Real-Time Polymerase Chain Reaction/*methods ; Republic of Korea ; Sequence Analysis, DNA ; Time Factors ; Veterinary Medicine/*methods