和田 新平

ABSTRACT Mycobacterium montefiorense , a nontuberculous mycobacterium, is a causative agent of mycobacteriosis in aquatic animals, its type strain M. montefiorense ATCC BAA-256 being isolated from a moray eel. In this study, we report the complete ATCC BAA-256 genome sequence with a 5,693,452-bp-containing circular chromosome, 65.2% GC content, and 5,407 coding sequences.

Mycobacterium chelonae is a nontuberculous mycobacterium that causes infections in various animals, including humans. In this study, we report the draft genome sequence of M. chelonae subsp. bovis strain NJB1701, which was isolated from a Baikal seal (Pusa sibirica) in captivity in Japan.

Mycobacterium marinum is a slow-growing, photochromogenic nontuberculous mycobacterium, which can cause mycobacteriosis in various animals, including humans. Several cases of fish mycobacteriosis have been reported to date. Mycobacterium marinum has also been isolated from aquatic environmental sources such as water, sand, biofilms, and plants in the natural environments. Hence, we hypothesized that a wide variety of sources could be involved in the transmission of M. marinum. In this study, we tested this hypothesis by isolating M. marinum from various sources such as fish, invertebrates, seagrass, periphytons, biofilms, sand, and/or water in two aquaria in Japan and conducting a phylogenetic analysis based on single-nucleotide polymorphisms (SNPs) using whole-genome sequences of the isolated strains. The analysis revealed that the strains from animal and environmental sources belonged to the same clusters. This molecular-based study epidemiologically confirmed that various sources, including fish, invertebrates, and environmental sources, could be involved in transmission of M. marinum in a closed-rearing environment. This is the first report where M. marinum was isolated from different sources, and various transmission routes were confirmed in actual cases, which provided essential information to improve the epidemiology of M. marinum.

INTRODUCTION: Mycobacterium montefiorense is one of the causes of non-tuberculous mycobacterial infections in moray eels and salamanders. Although M. montefiorense infection could be a threat to salamanders, little information is available regarding this pathogen and associated infection. This study aimed to provide fundamental information regarding M. montefiorense and its infection in salamanders. METHODS: Nine M. montefiorense strains isolated from three species of salamanders, namely, Japanese black salamander (Hynobius nigrescens), Hakuba salamander (H. hidamontanus), and Tohoku hynobiid salamander (H. lichenatus), between 2010 and 2018, were characterized based on phenotypic and genetic examination. We also pathologically observed salamanders infected with the M. montefiorense strains, including Hakuba salamanders and Tohoku hynobiid salamanders. RESULTS: The microbiological and chemical characteristics of the M. montefiorense salamander and an eel strain (reference strain) matched. Susceptibility testing for antimicrobials suggested that clarithromycin may be effective. Regarding disinfectants, phtharal, peracetic acid, glutaral, sodium hypochlorite, and benzalkonium chloride may be effective. Phylogenetic analyses revealed that the strains isolated from salamanders in 2014 and 2018 were genetically closely related, which could indicate an outbreak. The main gross findings in infected salamanders include skin ulcerative lesions or nodules in the enlarged liver. Microscopically, multifocal to coalescent granulomatous lesions composed of massive macrophages containing numerous acid-fast bacilli were prominently observed in the liver. CONCLUSION: This study contributes to our understanding of the genetic diversity and phenotypic characteristics of M. montefiorense, as well as the pathology of the infection.

クジラ型パラコクシジオイデス症 （paracoccidoioidmycosis ceti：PCM-C) は，イルカを宿主とし，難治性慢性肉芽腫性ケロイド状皮膚炎を特徴とする人獣共通真菌症である。原因菌は非培養性の Paracoccidioides brasiliensis var. ceti で，中南米を流行地とする高度病原性真菌症のパラコクシジオイデス症（PCM） の原因菌 P. brasiliensisと遺伝子型は同一である。確定診断は臨床症状と病理像での酵母細胞の証明であるが，遺伝子情報による診断も重要である。今回，遺伝子情報を欠くものの，PCM-Cが疑われていたイルカ皮膚病変生検組織よりnested-PCRで原因菌の特異的糖タンパク抗原遺伝子であるgp43が検出され，配列は既報のPCM-C国内第３症例目と98.9％相同であった。そこでPCMの診断用に設計されたLAMP法を応用したところ，PCRとLAMP法の組み合わせによりgp43の増幅に成功したことから，この手法は迅速診断法としての有用性が期待できる。

Nontuberculous mycobacterial (NTM) infections in humans have increased in prevalence in recent decades. Mycobacterium kansasii is one of the most prevalent human pathogenic NTM species worldwide. Herein, we report the first isolation of M. kansasii from an indoor domestic cat in Japan. Comparative genome sequence analysis of the feline isolate showed this pathogen is genetically identical to human pathogenic M. kansasii. This finding suggests that M. kansasii has a potential risk of zoonoses and requires the "One Health" approach to control NTM infection.

The skin disease paracoccidioidomycosis ceti occurs in several dolphin species globally. Infection by the unculturable fungi Paracoccidioides brasilensis or other Paracoccidioides spp. results in chronic cutaneous and granulomatous lesions. In this study we used immunohistochemistry to investigate the seroprevalence of antibodies to Paracoccidioides spp. in captive dolphins from three aquaria in Japan. We had previously reported that there were serological cross-reactions for Paracoccidioides spp. with related species in the order Onygenales. We hypothesized that the degree of serological cross-reactions for Paracoccidioides spp. might be lower in areas, such as Japan, where the fungal diseases coccidiodomycosis and paracoccidiodomycosis are not endemic. Sera from 41 apparently healthy dolphins, including 20 Atlantic bottlenose dolphins (BD: Tursiops truncatus), 6 Indo-Pacific bottlenose dolphins (IPBD: Tursiops aduncus), 2 F1 generation of a cross between BD and IPBD (F1), 3 Pacific white-sided dolphins (PWD: Lagenorhynchus obliquidens), 2 pantropical spotted dolphins (PSD: Stenella attenuata), 6 false killer whales (FKW: Pseudorca crassidens), and 2 rough-toothed dolphins (RTD: Steno bredanensis) were investigated. Sera from three dolphins with paracoccidioidomycosis ceti were used as a positive control. The yeast-form cells of Paracoccidioides spp. in the cutaneous tissue sample derived from the first Japanese paracoccidioidomycosis ceti case were used as the antigen for the immunohistochemistry. Of the 41 dolphins tested, 61.0% had antibodies against Paracoccidioides spp. This indicates that dolphins of several species in Japanese aquaria have likely been exposed to the pathogen Paracoccidioides spp.

The temperature of water used to rear juvenile stages of ayu affects the development of the thymus. However, subsequent differences in the thymus in adults after rearing juveniles at different temperatures are unclear. We analyzed thymus development of ayu grown at a constant water temperature of 15 degrees C from juveniles reared at different water temperatures. Juvenile ayu weighed at 0.6 g and 1.4 g were reared at different temperatures (10 degrees C, 12 degrees C, 15 degrees C, 18 degrees C and 22 degrees C) for 64 days and 54 days, respectively, and then held at 15 degrees C for analysis of the thymus development. Thymus volume was measured by computed tomography and thymus development of experimental fish was evaluated as the ratio of thymus volume to body length. The thymus volume ratios of juveniles immediately after rearing at lower water temperatures (10 degrees C, 12 degrees C) were higher than in those reared at the higher temperatures (18 degrees C, 22 degrees C). These levels of thymus volume ratio were preserved in grown ayu continuously reared at 15 degrees C. After the summer solstice, the thymus began to atrophy and no longer exhibited differences among the experimental groups. Thus the thymus formed at the juvenile stage retains its morphological properties until the summer solstice.

Mycobacterium montefiorense is a member of the Mycobacterium simiae complex, the largest group of nontuberculous mycobacteria. Here, we report the genome sequence of M. montefiorense isolate BS, isolated from diseased Japanese black salamander (Hynobius nigrescens) reared in an aquarium in Japan. This is the first reported case of an M. montefiorense infection in an amphibian.

A previously undescribed rapidly growing, non-pigmented mycobacterium was identified based on biochemical and nucleic acid analyses, as well as growth characteristics. Seven isolates were cultured from samples collected from five thread-sail filefish (Stephanolepis cirrhifer) and two farmed black scraper (Thamnaconus modestus). Bacterial growth occurred at 1535 degrees C on Middlebrook 7H11 agar. The bacteria were positive for catalase activity at 68 degrees C and urease activity, intermediate for iron uptake, and negative for Tween 80 hydrolysis, nitrate reduction, semi-quantitative catalase activity and arylsulfatase activity at day 3. No growth was observed on Middlebrook 7H11 agar supplemented with picric acid, and very little growth was observed in the presence of 5% NaCl. a-and a-mycolates were identified in the cell walls, and a unique profile of the fatty acid methyl esters and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) profiles of the protein and cell-wall lipids were acquired. Sequence analysis revealed that the seven isolates shared identical sequences for the 16S rRNA, rpoB, hsp65, recA and sodA genes. Phylogenetic analysis of the five gene sequences confirmed that the isolates were unique, but closely related to Mycobacterium chelonae. Antibiotic susceptibility testing revealed the minimum inhibitory concentration (MIC) of clarithromycin against this novel species was <0.25 mu g ml(-1), which was lower than that for Mycobacterium salmoniphilum. The hsp65 PCR restriction enzyme analysis pattern differed from those of M. chelonae and M. salmoniphilum. Based on these findings, the name Mycobacterium stephanolepidis sp. nov. is proposed for this novel species, with the type strain being NJB0901(T) (= JCM 31611(T) = KCTC 39843(T)).

Lacaziosis, formerly called as lobomycosis, is a zoonotic mycosis, caused by Lacazia loboi, found in humans and dolphins, and is endemic in the countries on the Atlantic Ocean, Indian Ocean and Pacific Ocean of Japanese coast. Susceptible Cetacean species include the bottlenose dolphin (Tursiops truncatus), the Indian Ocean bottlenose dolphin (T. aduncus), and the estuarine dolphin (Sotalia guianensis); however, no cases have been recorded in other Cetacean species. We diagnosed a case of Lacaziosis in a Pacific white-sided dolphin (Lagenorhynchus obliquidens) nursing in an aquarium in Japan. The dolphin was a female estimated to be more than 14 years old at the end of June 2015 and was captured in a coast of Japan Sea in 2001. Multiple, lobose, and solid granulomatous lesions with or without ulcers appeared on her jaw, back, flipper and fluke skin, in July 2014. The granulomatous skin lesions from the present case were similar to those of our previous cases. Multiple budding and chains of round yeast cells were detected in the biopsied samples. The partial sequence of 43-kDa glycoprotein coding gene confirmed by a nested PCR and sequencing, which revealed a different genotype from both Amazonian and Japanese lacaziosis in bottlenose dolphins, and was 99 % identical to those derived from Paracoccidioides brasiliensis; a sister fungal species to L. loboi. This is the first case of lacaziosis in Pacific white-sided dolphin.

In 2009 and 2010, unusually high mortality events were recorded among cultured populations of thread-sail filefish Stephanolepis cirrhifer in Ehime Prefecture, Japan. Diseased fish exhibited abdominal distention and many white nodules filled with thick, pale-yellow material scattered on the surface of the serosae of internal organs and mesentery. Histopathologically, the disease was characterized by variable sized granulomatous lesions with central necrotic core surrounded by thin irregular arrangement of epithelioid cells and the outermost thin rim of connective tissue. The central part of granuloma showed colliquative necrosis with abundant cellular debris and some clusters of long-rods that were positive with Ziehl-Neelsen stain. From the results of microbiological examinations and simplified identification with DNA-DNA hybridization, two representative isolates collected in 2009 and 2010 were classified into rapidly growing "nontuberculous mycobacteria (NTM)" that closely related to Mycobacterium chelonae. A pathogenicity test using one of the isolates successfully reproduced the granulomatous lesions closely resembled to those in the spontaneous cases, suggesting that the rapidly growing NTM is pathogenic to the thread-sail filefish, and is a causative agent of the spontaneous case. This is the first report of the disease caused by a rapidly growing NTM in maricultured fish in Japan.

The objective of this study was to locate the functional region responsible for the chemotaxis-inducing activity of flounder interleukin 8 (IL-8), which lacks the glutamic acid-leucine-arginine (ELR) motif essential for the induction of neutrophil migration by mammalian IL-8. Using a human cell line, we produced a secretory recombinant protein of flounder IL-8, and analyzed its chemotaxis-inducing activity on leukocytes collected from the flounder kidney. The recombinant IL-8 induced significant migration in neutrophils, which were morphologically and functionally characterized. Using the Edman degradation method, the N-terminal amino acid sequence of rIL-8 was identified as VSLRSLGV. To examine the significance of the N-terminal region for the bioactivity of flounder IL-8, we prepared several recombinant proteins that containing mutations at the N-terminus. Modification of three residues (residues 9-11: serine-leucine-histidine) corresponding in position to the ELR motif in mammalian IL-8 did not reduce its chemotaxis-inducing activity. However, deletion of the first six or more residues significantly reduced its chemotaxis-inducing activity. We propose that residue 6 (leucine) at the N-terminus is important for the chemotaxis-inducing activity of flounder IL-8. (C) 2014 Elsevier Ltd. All rights reserved.

In 2008, several episodes of mortality were recorded in cultured populations of juvenile greater amberjack reared in the southwest region of Japan. Diseased fish had asymmetrical abdominal distention and pale gills. The head kidney, trunk kidney, and spleen of every fish that was examined was enlarged and discolored. The results of all microbiological and molecular biological assays of tissues taken from diseased fish were negative for major known pathogens. Histopathologically, the disease was characterized by proliferative interstitial nephritis and proliferative splenitis associated with minute, round structures within the cytoplasm of proliferating mono-nucleated cells. Transmission trial using the enlarged trunk kidney from a naturally infected fish successfully reproduced the disease. The results indicate that this disease is caused by an infectious microorganism, and the most likely etiological agent is the minute, round structures which are probably a hitherto unknown eukaryotic microorganism.

The rapidly growing mycobacterium M. abscessus sensu lato is the causative agent of emerging pulmonary and skin diseases and of infections following cosmetic surgery and postsurgical procedures. M. abscessus sensu lato can be divided into at least three subspecies: M. abscessus subsp. abscessus, M. abscessus subsp. massiliense, and M. abscessus subsp. bolletii. Clinical isolates of rapidly growing mycobacteria were previously identified as M. abscessus by DNA-DNA hybridization. More than 30% of these 117 clinical isolates were differentiated as M. abscessus subsp. massiliense using combinations of multilocus genotyping analyses. A much more cost-effective technique to distinguish M. abscessus subsp. massiliense from M. abscessus subsp. abscessus, a multiplex PCR assay, was developed using the whole-genome sequence of M. abscessus subsp. massiliense JCM15300 as a reference. Several primer sets were designed for single PCR to discriminate between the strains based on amplicons of different sizes. Two of these single-PCR target sites were chosen for development of the multiplex PCR assay. Multiplex PCR was successful in distinguishing clinical isolates of M. abscessus subsp. massiliense from samples previously identified as M. abscessus. This approach, which spans whole-genome sequencing and clinical diagnosis, will facilitate the acquisition of more-precise information about bacterial genomes, aid in the choice of more relevant therapies, and promote the advancement of novel discrimination and differential diagnostic assays.

Mycobacteria isolated from epizootics of farmed fishes in western Japan were examined for the first time using multigenotypic analysis. By analysis of the sequences of the internal transcribed spacer between the 16S and 23S rRNA genes (ITS) region and the partial 16S rRNA, hsp65 and rpoB genes, M. pseudoshottsii was identified as the causative agent in these infections. Prior to this study, only M. marinum has been known as the causative agent of lethal mycobacterial disease in marine fishes in Japan.

In this study, black disease infecting fairy shrimps, Streptocephalus sirindhornae Sanoamuang, Murugan, Weekers & Dumont, and Branchinella thailandensis Sanoamuang, Saengphan & Murugan, in Thailand, was investigated. The typical signs of the disease are the appearance of black spots on the cuticle, located mainly on the dorsal side and thoracopods. A number of rod-shaped bacteria aggregated in the black spots and were visualized by scanning electron microscopy. The histopathological results showed that a haemocytic response to the infection resulted in a dense melanized core of bacteria. In addition, generalized septicaemia by rod-shaped bacteria was also observed in the infected tissue. Of the 31 isolates, Aeromonas spp. were predominantly isolated and six strains were selected for the experimental infections. The most pathogenic strain was identified molecularly as A. hydrophila. When fairy shrimp were infected at bacterial concentrations of 10(4) and 10(6) cfu mL(-1), the overall infection levels were 73.33 +/- 6.67% and 93.33 +/- 6.67%, respectively. The experimentally infected fairy shrimp showed abnormal swimming and died within 24-48 h after the appearance of the dark pigment.

A species of Aphanomyces was isolated from juvenile soft-shelled turtles, Pelodiscus sinensis, cultured in Japan. Typically, an infected turtle showed small whitish maculae on the carapace. Many hyphae were observed in the epidermis. The hyphae were isolated using glucose-yeast (GY) agar plates. The morphological characteristics were very similar to those of Aphanomyces laevis, but a clear nuclear spot was observed in the center of the oospore in the strains isolated from the soft-shelled turtles. The optimal growth temperature for the isolates was 25-30A degrees C and the optimum pH was 6-9. Experimental infection tests with isolates produced small whitish maculae on the carapace, and soft-shelled turtles artificially infected with the zoospores showed high mortality, especially in the high-dose group. Phylogenetic analysis based on the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) indicated that the isolates from the soft-shelled turtles were unidentified species of Aphanomyces. As a result, the strain was described as a new species, Aphanomyces sinensis.

In this study, we aimed to identify the leukocyte population that expresses Fas ligand (FasL) in the Japanese flounder (Paralichthys olivaceus). The transcriptional activity of FasL was examined for the first time in the fish leukocytes. Transcription of the FasL gene in flounder leukocytes was significantly increased by phytohemagglutinin (PHA) treatment. All the leukocyte populations we tested possessed binding activity for PHA, but this was especially high in the lymphocyte population. However, the lymphocytes consisted of two subsets showing heterogeneity with respect to PHA binding, with the high-binding subset being surface IgM-negative. We also found that only the lymphocyte population showed a significant increase in the expression of the FasL gene after stimulation with PHA. In addition, only the lymphocyte subset showing high binding to PHA showed conspicuous expression of the FasL gene. This subset also had a CD3 gamma/delta (+), CD8 alpha (+) and IgM heavy-chain (-) phenotype. These results suggested that lymphocytes with T-cell-like properties are FasL-expressing cells in the Japanese flounder. (C) 2010 Elsevier Ltd. All rights reserved.

The role of leukocytes from the kidney of Japanese flounder Paralichthys olivaceus in the encapsulation response was investigated using an in vitro model. The aggregation response of leukocytes to the target fish pathogen Ichthyophonus hoferi was observed over 12 h. The cellular aggregates mainly comprised granulocytes, which were characterized by intracellular peroxidase expression. Moreover, studies of isolated granulocytes demonstrated their adhesion to I. hoferi and formation of an initial layer in the encapsulation response. We observed that mRNA expression levels of three CC-chemokines (CCL3, CCL4 and CC-CLM) and one CXC-chemokine (IL-8) increased during the encapsulation process. Among these chemokines, CC-CLM and IL-8 were actively produced by granulocytes upon stimulation by I. hoferi. Flounder granulocytes therefore appeared to play an important role in the process by releasing specific chemokines upon pathogen recognition, thereby inducing subsequent cellular recruitment leading to encapsulation.

Acremonium sp. NJM 0672, isolated from diseased mantis shrimp Oratosquilla oratoria, was susceptible in vitro to three kinds of antifungal agents: voriconazole, amphotericin B and terbinafine hydrochloride. Voriconazole was selected to treat kuruma prawn Penaeus japonicus, which had been intramuscularly injected with 0.1 mL of 5.0 x 10(4) conidia/mL of Acremonium sp. Voriconazole was administered orally at doses of 6 and 2 mg/kg body weight per day for 7 consecutive days, or intramuscularly injected at doses of 4 and 2 mg/kg body weight per day for 3 consecutive days. Both treatments were begun at 6 h after injection of the conidial suspension. The gross features, mortality and histopathological findings demonstrated that voriconazole was an efficient antifungal agent against Acremonium sp.

A visceral mycosis occurred in ayu Plecoglossus altivelis larvae at Yamanashi Prefectural Fisheries Technology Center, Japan, in 2007 and 2008. Cumulative mortalities due to the disease were 19-33%. Most diseased fish were characterized by the opaque abdomen. Abundant non-septate hyphae with a width of approximately 5 pm were observed in the opaque areas. Fungi isolated from diseased fish were all identified as Pythium flevoense based on the morphological characteristics and sequence analysis of the 5.8S rDNA and adjacent ITS regions. Histopathological examinations showed that non-septate hyphae were present in the airbladder, kidney, intestine, pancreas, spleen, abdominal cavity, musculature and spinal cord. Heavy hyphal propagation in the airbladder and rhexis of the organ suggested that accidental ingestion of P flevoense into the airbladder was the prime cause of this disease.

This report describes Exophiala infection in cultured striped jack, Pseudocaranx dentex, in Japan in 2005. One hundred out of 35 000 fish died per day and mortalities continued for 1 month. Diseased fish showed swelling of the abdomen and kidney distension. Numerous septate hyphae, pale brown in colour, were seen in kidney in squash preparations. Histology revealed abundant fungal hyphae and conidia in gill, heart and kidney. Fungal hyphae were accompanied by cell necrosis and influx of inflammatory, mainly mononuclear cells. The fungus isolated from the diseased fish had septate hyphae, pale brown in colour and 1.8-3.0 mu m in diameter. Conidiogenous cells were conspicuous annellides, short or cylindrical or fusiform in shape. Conidia were one-celled, ellipsoidal with smooth walls, accumulated in balls at the apices of annellides that tended to slide down, 1.5-2.0 mu m in width and 3.0-5.0 mu m in length. The fungus was classified into the genus Exophiala based on its morphology and as Exophiala xenobiotica based on the sequences of the ITS 1-5.8S-ITS 2 regions of rDNA. This is the first record of this fungus in a marine fish.

This study compared the histopathology of young striped jack Pseudocaranx dentex experimentally infected with the dematiaceous fungus Ochroconis humicola NJM 0472 with that of spontaneously infected fish. Moribund and freshly dead fish from both groups showed similar histopathology, and appeared to have been killed due to hyphae penetrating the visceral organs. Fish that survived the infection appeared to be able to suppress the fungal growth by well-established inflammatory reaction involving mycotic granulomas and granulation tissues. The results suggested that two types of O. humicola infection occur in young striped jack: an acute type infection, which is characterized by penetrating hyphae that cause direct tissue destruction and a chronic type infection, which is characterized by severe inflammatory reaction that causes functional disorders of the affected organs.

下等菌に起因する疾病がドワーフグラミーに発生した. 病魚の多くは腹部膨満を呈したが, 腹水の貯留は認められなかった. 筋肉および内臓諸器官の圧扁標本中に無隔で分枝した菌糸が存在した. 病理組織学的に内臓諸器官および筋肉内に菌に起因する肉芽腫が多数観察された. 病魚からの菌の分離は困難なことが多いが, これは体内では菌がすでに死滅していることが多いためと推察された. 分離菌はすべて Aphanomyces sp. に同定された. 本菌の各種性状はアユの真菌性肉芽腫症原因菌, A. piscicida に類似したが, 若干の差異も見られた.

Fusarium moniliforme was isolated from gill lesions of kuruma prawn Penaeus japonicus, with black gill disease at a private farm in Okinawa Prefecture in 1989. The colonies of the fungus cultured on upper surface of potato dextrose agar were floccose, creamy white, undersurface a lavender to violet, but did not grow on mycobiotic agar containing cycloheximide. The present report describes the first case of F. moniliforme infection in crustacea. An experimental infection using kuruma prawn was made by intramuscular injection with the conidia of F. moniliforme NJM 8995. For comparison, Fusarium solani NJM 8996 isolated also from a kuruma prawn with black gill disease in Okinawa Prefecture in 1989, was used as a reference. The clinical signs and pathological findings of the disease caused by the two species of the fungi were similar. Identification of the fungi isolated from the lesions was based principally upon the cultural characteristics. The use of a media lacking cycloheximide is recommended for the isolation of F. moniliforme.

1984年12月下旬から1985年1月中旬にかけて, 神奈川県淡水魚増殖試験場の屋内にあるアユ稚魚飼育層の稚魚にへい死を伴う疾病が発生した。瀕死魚(体長:約3cm)の肉眼的所見は腹水貯溜を伴う腹部膨満および肝臓のうっ血・腫大であった。病理組織学的に検索した結果, 顕著な病変は心室に認められた血栓であった。アユ稚魚の死因はまず何らかの原因で心室筋に変性・壊死が生じ, 次いで血栓が形成され, それが高度になるに伴って全身状態が悪化したためと判断した。

1985 年 4月, 香川県内の一種苗生産場のヒラメ稚魚に累積へい死率が約 50 ％に達する疾病が発生した。瀕死魚の外部所見は腹部膨満, 鰓の貧血, 肛門の発赤などで, 内部所見は肝臓のうっ血, 腸の発赤などであった。細菌, ウイルスおよび寄生虫学的検査はいずれも陰性であった。病理組織学的検査の結果, 特徴的病変は心房内に形成された血栓および心筋の変性であったことから, 死因は何らかの原因で心房筋に変性が生じ, 次いで心房内に除々に血栓が形成され, やがて全身状態が悪化したためと判断した。

Studies were made on histopathology of cultured tiger puffer with “Kuchijiro-sho” collected from some fish farms in Nagasaki Prefecture from July to December, 1984. The fish were characterized by erosion and ulceration of the mouth, dark body coloration and biting aggressively each other. Internally, linear superficial hemorrhage in the liver was commonly observed. The main histopathological change was found in the large nervous cell at the nucleus of the 8∼10th cranial nerve and supramedullary neuron. The change was characterized by formation of some masses in the nucleus and the deformed shape of the nucleus of the large nervous cell and supramedullary neuron. The mass in the nucleus had slight change of coloration for some kinds of stain. Electron-microscopical examination was made on the nucleus of cranial nerves of the medulla oblongata as a result, virus-like particles were observed either as a mass-type in the nucleus or as scattering-type on the deformed nuclear membrane. Judging from the histopathological and electron-microscopical findings, a possibility was suggested that the disease called “Kuchijiro-sho” was caused by virus infection. © 1985, The Japanese Society of Fish Pathology. All rights reserved.