proliferative kidney disease

A detailed review of proliferative kidney disease (PKD) in salmonids is presented. The introduction places the disease in a historical context. The various aspects of the disease are described from the existing literature, together with latest findings from current research. Particular emphasis is given to epidemiology, aetiology and pathology.

Proliferative kidney disease PKD of salmonid fish is an endoparasitosis due to infection with an, as yet, unclassified myxosporean parasite, the so-called 'PKX'. Malachite green and fumagillin are the only chemotherapeutants capable of controlling this disease. The efficacy of a single Ž. y1 y1

Monoclonal antibody B4 (mAb B4) was previously developed to the myxozoan parasite Tetracapsuloides bryosalmonae Canning, Curry, Feist, Longshaw et Okamura, 1999, the causative agent of proliferative kidney disease of salmonids. Here we describe the reaction of mAb B4 against Myxobolus cerebralis Hofer, 1903, the parasite that causes 'whirling disease' in salmonids. Tissues examined were collected from experimentally infected rainbow trout Oncorhynchus mykiss (Walbaum) and the aquatic oligochaete Tubifex tubifex (O.F. Müller), the two hosts involved in the life cycle of M. cerebralis. Paraffin sections of infected rainbow trout taken at 4 h and 3, 10, 17 and 54 days post-exposure to infective M. cerebralis actinospores were immunohistochemically stained with mAb B4. Longitudinal sections through infected T. tubifex sampled 120 days post-exposure to M. cerebralis myxospores were also examined using this method. The only phase of the M. cerebralis life cycle that expressed the mAb B4 antigen was during sporogenesis in the salmonid host. The immunohistochemical staining demonstrated that the antigen was released into the tissues surrounding the spore and sporogonic stages of the parasite. The localisation of the antigen was diffuse in the fish, suggesting that the possible effect of M. cerebralis infection is extensive through the head tissues and not limited to areas of cartilage destruction as previously thought.

The lectin GS-I (Griffonia siniplicifol~a agglut~nin-I) and a recently developed monoclonal antibody (Mabl2) both recognized extrasporogonic (interstitial) and sporogonic (intraluminal) stages of the PKX myxosporean causing proliferative kidney disease (PKD) in salmonid fish. In histochemical and immunostains the lectin and antibody recognized PKX from North American and European salmonids including Atlantic salmon Salmo salar, chinook salmon Oncorliynchus tshawytscha, coho salmon Oncorhynchus kisutch, brown trout Salmo trutta, and grayling Thymallus thymallus. Although the specific structures recognized by the lectin and Mabl2 were not determined, double fluorescent staining techniques showed similar staining patterns with extrasporogonic or interstitial stages of the PKX myxosporean. An apparent inhibition between the lectin and Mabl2 in these double stains suggests that they recognize similar structures of the parasite. Sporogonic stages of PKX, some containing polar capsules, were detected with the lectin and Mabl2 stains in fish with typical extrasporogonic (interstitial) P M providing further confirmation of the relatedness of these stages. Both the lectin and 1Mabl2 provide useful tools for further study of the epidemiology of the PKX myxosporean, for future development of tests to detect anti-parasite antibodies in fish serum and for the identification of potential imrnunogens for vaccination of trout.

The antibiotic Fumagillin DCH was found to be effective in controlling experimental infections with PKX, the myxosporean that causes proliferative kidney disease (PKD) in salmonid fish. Following 6 or 7 wk of treatment, experimentally infected chinook salmon Oncorhynchus tshawytscha showed no evidence of PKX cells, or of the renal inflammation characteristic of PKD, on withdrawal of the treatment and tor up to 7 wk afterwards. In contrast, 90 to 100 % of fish (in 2 experiments) that were injected with PKX, but not glven the antibiotic, had numerous PKX cells in the kidney and developed clinical PKD. This is the first report of an effective orally administered drug for the control of a myxozoan infection in salmonid fish.

The myxozoan parasite Tetracapsuloides bryosalmonae is the causative agent of proliferative kidney disease (PKD), a highly damaging disease of cultured salmonid fish. Within this study, phylactolaemate bryozoans were collected from a river known to be endemic for PKD and subsequently cultured in the laboratory. Sequential developmental stages of T. bryosalmonae were studied by light microscopy within the living bryozoan colonies, allowing the identification of stages attached to host peritoneum, consistent with previous molecular evidence of cryptic stages. Infection resulted in the production of large numbers of spores, which were released from the bryozoans. Experimental exposure of rainbow trout (Oncorhynchus mykiss) to medium in which infected bryozoans were cultured resulted in clinical PKD. Rainbow trout were exposed to known numbers of T. bryosalmonae spores collected by micromanipulation, which had been released from mature spore sacs within colonies of the bryozoan Fredericella sultana. Exposure to one spore was sufficient to lead to development of PKD. These findings indicate that small numbers of bryozoans are capable of releasing sufficient spores to infect large numbers of fish, having implications for future control methods for PKD in salmonid farming.

Infectious diseases represent a limiting factor for the further development of Italian aquaculture. The recent introduction and spreading of new pathogens, along with the global climatic change, has contributed to a considerable decrease in trout production. Emerging pathologies in rainbow trout culture include viral diseases, e.g. infectious haematopoietic necrosis (IHN), bacterial diseases, such as lactococcosis and visceral flavobacteriosis, and parasitical diseases, e.g. proliferative kidney disease (PKD). Higher mortality rates in trout fry and fingerlings are generally induced by visceral flavobacteriosis and IHN, while the main losses in large trout during the warm season are due to lactococcosis and PKD. Mariculture has at present a better sanitary status compared to trout culture, but a rapid dissemination of pathogens, including zoonosis agents, is envisaged also for seabass and seabream. Emerging pathologies in sea bass include VNN, pseudotuberculosis, streptococcosis and tuberculosis. Seabream is much more resistant and is mainly affected by novel V ibrio infections and enteromyxidiosis. A good sanitary management of fish farms is essential for avoiding or limiting losses caused by emerging pathologies. Transmission of zoonosis agents to man, through the consumption of cultured fish, is very remote in Italy. On the contrary, transmission of Streptococcus iniae, V ibrio vulnificus and Mycobacterium marinum by means of improper manipulation of infected fish, could represent a potential hazard for fish farmers and fish processors, as well as for people preparing fish meals.

Proliferative kidney disease PKD of salmonid fish is an endoparasitosis due to infection with an, as yet, unclassified myxosporean parasite, the so-called 'PKX'. Malachite green and fumagillin are the only chemotherapeutants capable of controlling this disease. The efficacy of a single Ž. y1 y1

Considerable mortality among 0+ Atlantic salmon Salmo salar L. was seen in the River Åelva, Central Norway, in 2002, 2003, and 2004 (E. Sylten pers. comm.). This river is regulated for hydroelectric power purposes, and management authorities suggested that oxygen deficiency during periods with low water discharge and high temperatures was the reason for the observed mortality. Thus, temperature and oxygen concentrations were monitored throughout the summers of 2005 and 2006. No mortality was reported in 2005, but in 2006 fish mortality was once again seen during a period when oxygen monitoring showed far from lethal levels (8 to 9 mg O 2 l-1), suggesting that the observed mortality was caused by disease. At autopsy, dead fish collected in the river were found to have pale and enlarged kidneys. Prolif

Infectious diseases represent a limiting factor for the further development of Italian aquaculture. The recent introduction and spreading of new pathogens, along with the global climatic change, has contributed to a considerable decrease in trout production. Emerging pathologies in rainbow trout culture include viral diseases, e.g. infectious haematopoietic necrosis (IHN), bacterial diseases, such as lactococcosis and visceral flavobacteriosis, and parasitical diseases, e.g. proliferative kidney disease (PKD). Higher mortality rates in trout fry and fingerlings are generally induced by visceral flavobacteriosis and IHN, while the main losses in large trout during the warm season are due to lactococcosis and PKD. Mariculture has at present a better sanitary status compared to trout culture, but a rapid dissemination of pathogens, including zoonosis agents, is envisaged also for seabass and seabream. Emerging pathologies in sea bass include VNN, pseudotuberculosis, streptococcosis and tuberculosis. Seabream is much more resistant and is mainly affected by novel V ibrio infections and enteromyxidiosis. A good sanitary management of fish farms is essential for avoiding or limiting losses caused by emerging pathologies. Transmission of zoonosis agents to man, through the consumption of cultured fish, is very remote in Italy. On the contrary, transmission of Streptococcus iniae, V ibrio vulnificus and Mycobacterium marinum by means of improper manipulation of infected fish, could represent a potential hazard for fish farmers and fish processors, as well as for people preparing fish meals.

En principe inoffensifs, certains bryozoaires, marins ou dulcicoles, peuvent néanmoins
créer des nuisances, par exemple, en provoquant des allergies, en colonisant des coques de navires, en obstruant des conduites ou des prises d'eau ou en servant d'hôte intermédiaire à des parasites de poissons d'eau douce. D'autres, bien utiles, contiennent des substances aux potentialités thérapeutiques prometteuses.