Fish Pathology
Online ISSN : 1881-7335
Print ISSN : 0388-788X
ISSN-L : 0388-788X
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  • Takamitsu Sakai
    Type: Review
    2021 Volume 56 Issue 1 Pages 1-5
    Published: March 15, 2021
    Released: April 22, 2021

    Redmouth disease is caused by the infection of the enteric bacterium Yersinia ruckeri. ​The disease was first noticed in rainbow trout Oncorhynchus mykiss in the USA in 1950s and has since been observed in salmonids and some other fishes in many countries. ​Y. ruckeri can be classified into different biotypes, serotypes, or genotypes, according to biological properties such as motility or enzyme activity, antigenicity, or gene sequences. ​In particular, O-antigen, which is one of the markers for serotyping, is an important antigen for the vaccination for of Y. ruckeri. ​In Japan, redmouth disease is listed as one of the notifiable diseases of aquatic animals by the government to prevent occurrences or spreading of the disease. ​This review describes topics necessary important for the diagnosis and control of the disease.

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Research Article
  • Tsuyoshi Katou, Mayuka Kitamura, Tomoki Maeda, Tomoyuki Odaka, Fumio T ...
    Type: Research Article
    2021 Volume 56 Issue 1 Pages 6-13
    Published: March 15, 2021
    Released: April 22, 2021

    Kuchijirosho is a lethal infectious disease of fugu Takifugu rubripes, and the causative pathogen has been predicted to be an RNA virus. ​Although the homogenate of kuchijirosho-affected brain is pathogenic to fugu, the suspected viral particles have not been found in the brain and the viral genome has not been isolated. ​We attempted to clone the cDNA of the kuchijirosho virus genome using the Rapid Determination System for Viral RNA Sequence method. ​Three cDNA segments of ca. 1,000 nt each, which could be parts of the viral genome, were obtained from total RNA extracted from the brains of fugu artificially infected with kuchijirosho. ​According to RT-qPCR, the brain had more of these three kuchijirosho-associated RNAs (KARs) than any other tissues. ​KARs in the brain were detected 1–2 days after injecting the homogenate of kuchijirosho-affected brain and KARs expression levels were increased rapidly until death. ​These results show that the detection of KARs can be sufficiently effective for the molecular diagnosis of kuchijirosho. ​Even if KARs are parts of the viral genome, it is unclear to which taxonomic family the kuchijirosho virus belongs, because the nucleotide sequences of KARs did not correspond to those of any other organisms including viruses.

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Short Communications