nocardiosis of fish
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IdentityTop of page
Preferred Scientific Name
- nocardiosis of fish
International Common Names
- English: granulomatous disease; nocardiosis
- French: nocardiose
Pathogen/sTop of page Nocardia
OverviewTop of page
Nocardiosis is a disease of both saltwater and freshwater fish caused by actinomycetes of the genus Nocardia. Cases of piscine Nocardia are not as widely reported as mycobacteriosis in fish. Some nocardial infections in fish may be misinterpreted as mycobacterial disease, as they both result in similar clinical signs and gross pathology. Nocardia asteroides, described by Eppinger in 1891, is considered the type species of the genus (Gordon and Mihm, 1962). Nocardia farcinica had been formerly regarded as the type species, but this was changed due to the absence of an authentic strain in any culture collection and the paucity of references to N. farcinica in the literature. The first case of fish nocardiosis caused by N. asteroides was reported in neon tetra, Hyphessobrycon innesi (Valdez and Conroy, 1963).
The taxonomy of bacteria in the genus Nocardia is not as well organized as in other groups (Austin and Austin, 1987), so there is a need for bacteriological taxonomists to modify the classification of nocardioform bacteria and help to eliminate any confusion.
[Based upon material originally published in Woo PTK, Bruno DW, eds., 1999. Fish diseases and disorders, Vol. 3 Viral, bacterial and fungal infections. Wallingford, UK: CABI Publishing.]
Host AnimalsTop of page
Hosts/Species AffectedTop of page
Information on fish nocardiosis is very limited in comparison with mycobacteriosis in fish. However, this does not mean that nocardial infection is less of a problem in fish than mycobacteriosis. Nocardia asteroides has been reported to be the cause of granulomatous disease in neon tetras kept in aquaria in Argentina (Conroy, 1964). Snieszko et al. (1964) reported nocardial infection in hatcheryreared fingerling rainbow trout, Oncorhynchus mykiss, in Lee Town, West Virginia, USA, and subsequently Campbell and MacKelvie (1968) isolated Nocardia in brook trout, Salvelinus fontinalis, from Canada. Nocardiosis was also observed in cultured yellowtails, Seriola quinqueradiata and Seriola purpurascens, in Japan (Kubota et al., 1968). An outbreak of nocardiosis was recorded in Formosa snakehead fish (Channidae) from Taiwan (Hsu et al., 1987). Nocardia seriolae was later isolated from cultured yellowtail (S. quinqueradiata) and Japanese flounder (Paralichthys olivaceus) (Kudo et al., 1988).
Nocardioform actinomycetic organisms were isolated from many species of freshwater fish affected with epizootic ulcerative syndrome (EUS) in India (Chakrabarty and Dastidar, 1991). Crayfish (Austropotamobius pallipes) have been reported with nocardial infection showing melanized nodules throughout the tail muscle (Fisheries and Oceans Canada, 2004a). Pacific oyster (Crassostrea gigas) are also susceptible to Nocardia sp., causing mortality during the hot season in several embayments in British Columbia, Canada and Washington state, USA (Friedman and Hedrick, 1991; Friedman et al., 1991).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 10 Jan 2020
PathologyTop of page
Histopathological examinations of infected organs have revealed characteristic granulomas, each with a centre of necrotic material, a peripheral cellular zone of numerous histiocytes, lymphocytes and a few multinucleated giant cells, all of which are partially circumscribed by a fibrous capsule. Engelhardt (1987) noted that colonies of weakly acid-fast bacteria were present within and at the periphery of several granulomas. Hsu et al. (1987) observed numerous disseminated abscesses, encapsulated by granulation tissue, in the pleura and viscera of infected Formosa snakehead fish.
DiagnosisTop of page
Nocardiosis is a systemic chronic granulomatous disease of fish caused by several species of the bacterium Nocardia. Severe emaciation, inactivity and skin discoloration are the clinical signs of this disease. In advanced stages, cachexia, ascites, dermal ulceration, focal necrotic areas within skeletal muscle and pale areas in the swollen kidney, spleen, heart and liver may be observed (Kubota et al., 1968). The appearance of small nodules on the gills of infected yellowtails has been reported (Kusuda et al., 1974).
As already mentioned, nocardiosis may be misdiagnosed as mycobacteriosis, because of the similarity between the clinical signs and gross pathology associated with the two diseases. Positive differentiation can only be made by isolation and identification of the causative agent. In addition, histological sections of the infected organs should be examined. Nocardioform bacteria can grow on similar kinds of media to mycobacteria. After 24 h of growth on nutrient agar, typical colonies of Nocardia are seen. These are raised, folded, granular or powdery, 1-4 mm in diameter, yellow or tan, and with aerial mycelium around the edges (Engelhardt, 1987). Nocardial granulomas without the epithelioid cells in the earliest stages of development are easily confused with piscine mycobacteriosis. Furthermore, while acid-fast organisms are present in the Nocardia lesion, they only show a positive reaction for Nocardia with Fite-Faraco acid-fast stain. Morphologically, Nocardia appear filamentous, branched and beaded and are 5-50 mm long, while mycobacteria are usually 1-3 mm in length (Wolke and Stroud, 1978).
More specific and sensitive methods have been applied for diagnosis including antibody-based and DNA based methods. Chen et al. (2000) described immunohistochemistry using polyclonal antibodies to detect Nocardia seriolae in sea bass. However, more specific probes such as monoclonal antibodies have not been employed yet.
Polymerase chain reaction (PCR), employing primers to the 16S-23S rRNA internal transcribed spacer, has also been used to detect Nocardia seriolae in yellowtail fish (Kono et al., 2002). As a sensitive and specific method, PCR could be useful for detection of the pathogen in both diseased fish and carriers.List of standard diagnostic tests with range of results.
|DNA probes- in situ hybridisation||-||+||+++|
- the method is presently unavailable or unsuitable; + the method has application in some situation but cost, accuracy or other factors severely limits; ++ the method is a standard method with good diagnostic sensitivity and specificity; +++ the method is the recommended method for reasons of availability, specificity and sensitivity.
List of Symptoms/SignsTop of page
|Finfish / Abscess - Skin and fins||Aquatic:Adult||Diagnosis|
|Finfish / Cessation of feeding - Behavioural Signs||Aquatic:Adult||Sign|
|Finfish / Change in cloudiness - Eyes||Aquatic:Adult||Diagnosis|
|Finfish / Creamy white nodules / granulomas - Organs||Aquatic:Adult||Diagnosis|
|Finfish / Cysts - Gills||Aquatic:Adult||Diagnosis|
|Finfish / Discoloration - Skin and fins||Aquatic:Adult||Diagnosis|
|Finfish / 'Dropsy' - distended abdomen, 'pot belly' appearance - Body||Aquatic:Adult||Sign|
|Finfish / Fish rubbing body on hard surfaces - Behavioural signs||Aquatic:Adult||Sign|
|Finfish / Generalised lethargy - Behavioural Signs||Aquatic:Adult||Sign|
|Finfish / Haemorrhaging - Body Cavity and Muscle||Aquatic:Adult||Sign|
|Finfish / Mortalities -Miscellaneous||Aquatic:Adult||Diagnosis|
|Finfish / Necrotic musculature - Body cavity and muscle||Aquatic:Adult||Sign|
|Finfish / Nodules - Gills||Aquatic:Adult||Diagnosis|
|Finfish / Pop-eye - Eyes||Aquatic:Adult||Diagnosis|
|Finfish / Scale loss - Skin and Fins||Aquatic:Adult||Diagnosis|
|Finfish / Ulceration - Skin and fins||Aquatic:Adult||Diagnosis|
Disease CourseTop of page
No studies have yet been undertaken on the pathogenicity of nocardioform bacteria. Kusuda et al. (1989) demonstrated that yellowtails immunized with attenuated live N. kampachi showed an increase in the number of active lymphocytes and granulocytes within 72 h.
EpidemiologyTop of page
The routes by which infection takes place are not known. Most cases of piscine nocardiosis involve the oral cavity, but, experimentally, oral exposure has not been established as a primary route of infection. Sindermann (1990) suggested that farmed fish may be infected via contaminated feed. In Atlantic salmon farms, Bransden et al. (2000) suggested that phylloplane flora containing a high proportion of Gram-positive bacteria may introduce the pathogen into fish tanks via falling leaf litter from the overhanging trees.
Impact SummaryTop of page
|Fisheries / aquaculture||Negative|
Zoonoses and Food SafetyTop of page
Several species of Nocardia are known to be human pathogens. For example, Nocardia asteroides frequently occur in immunocompromised patients. Nocardiosis is a suppurative disease of the lung and may spread to the brain and meninges. N. asteroids can also lead to cutaneous nocardiosis (Rapini and Shook, 2001). Although there is no report of disease transmission from fish to man via consumption, fish should be totally cooked. Infected fish should be also handled with great precaution.
ReferencesTop of page
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Money DJ, Hotchkiss PM, Smith CE, 2004. Nocardia-like filamentous bacteria causes mortality in juvenile Snake River cutthroat trout. In: American Fisheries Society/Fish Health Section, Fish Health Newsletter, 32 (3) 10-13.
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Whittington R J, Reddacliff L A, Marsh I, Kearns C, Zupanovic Z, Callinan R B, 1999. Further observations on the epidemiology and spread of epizootic haematopoietic necrosis virus (EHNV) in farmed rainbow trout Oncorhynchus mykiss in southeastern Australia and a recommended sampling strategy for surveillance. Diseases of Aquatic Organisms. 35 (2), 125-130. DOI:10.3354/dao035125
Distribution MapsTop of page
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