An ulcerative skin disease which is very similar clinically to that reported in Japanese eel (Anguilla japonica) has caused morbidity in both wild and cultured populations of American eel (A. rostrata) in North Carolina, USA. Lesions appear to begin as localized, depigmented foci which spread to form large patches of necrotic skin up to 16 cm2 in area. The depigmented patches detach at the dermo-epidermal junction, forming large ulcers that expose underlying muscle. The infection commonly affects the head, producing cranial swelling and corneal edema. A mild to severe, primarily mononuclear infiltrate is seen, most prominently in large ulcers. Many lesions had extensive collagen deposition, which contributed to the tissue swelling. Culture of skin lesions in various stages of development revealed the consistent presence of bacterial isolates that were biochemically and immunologically identified as Aeromonas salmonicida. This agent was the predominant organism by colony type in 17 of 20 skin cultures and usually appeared to constitute over 90% of the colonies present. Kidney samples were free of infection.
The viral interference exhibited by HB-1 virus, a strain of infectious pancreatic necrosis virus (IPNV) isolated from hard clam, Meretrix lusoria, was studied. The TO-2 cells infected with serial passage HB-1 virus at 100 to 10-4 dilutions showed that viral interference was related to the degree of dilution of virus inoculum. The specific viral antigens were detected with immunofluorescent antibody stain technique in TO-2 cells which survived from high multiplicity infection of HB-1 virus. The virus yield in culture fluid from a series of 20 serial undiluted or diluted passages indicated that serial undiluted or low-diluted (10-1 to 10-2) passaging of HB-1 virus could induce autointerference in TO-2 cells. The defective interfering (DI) particles in the virus samples were considered to be responsible for the interference. The SDS-PAGE analyses for the polypeptide composition of virions from serial diluted and undiluted passaging showed that there were differences in β group. The truncated β polypeptides were regarded to be specific polypeptides produced by DI particles generated by serial undiluted passaging. We, thus, provided new information concerning IPN DI particles by comparing the properties of the virions produced by serial diluted and undiluted passaging of HB-1 virus, a strain of IPNV.
The potential of fumagillin DCH to prevent proliferative kidney disease (PKD) in rainbow trout fingerlings was tested in field and laboratory studies. In a field study, PKX trophozoites and accompanying inflammation (PKD) occurred in the kidneys of 92.7% of fish fed control diets and in only 7.9% of fish receiving 0.34 g fumagillin/kg of diet (fed at 6% biomass per day) when examined 65 days after being placed in waters enzootic for the parasite. In a laboratory study, fumagillin treatment reduced the number of fish that developed PKD following natural exposure to the parasite. In both the laboratory and the field studies, fish fed fumagillin demonstrated a loss of appetite beginning 2 to 4 weeks following feeding of medicated diets. Cumulative mortalities of 92% and 33% for the field and laboratory studies were experienced by groups of fish continuously fed medicated diets. The toxicity of fumagillin was evaluated in the laboratory following feeding at 0.1, 0.25, 0.5 or 1.0 g drug/kg feed (fed at 1.5-2.0% biomass daily) for 8 weeks at water temperature of 15°C. Fish administered 0.5 and 1.0 g drug/kg food exhibited anorexia beginning 4 weeks after initiation of feeding that lasted until the end of the experiment at 8 weeks. The cumulative mortality of fish fed the 1.0 g drug/kg reached 22% at the end of the study. The average weight of these fish was significantly decreased compared to fish receiving lower doses or no fumagillin in the diet. The spleen and kidney of fish administered the two highest doses of fumagillin were grossly reduced in size. Microscopic examinations revealed a decrease in the amount of interstitial hematopoietic tissue in the anterior and posterior kidney and splenic lymphoid tissue. These effects were least apparent in the fish fed 0.1 g fumagillin/kg feed. These results indicate that fumagillin can have an adverse effect on the hematopoietic tissue of fish when administered at increased concentrations over an extended period of time. However, these effects can be minimized when fish are fed low doses of fumagillin as a potential treatment to prevent PKD.
Light and electron microscopical observations were made on the seasonal progress of developmental stages of Hoferellus carassii, the causative organism of kidney enlargement disease (KED). In October to November, an early stage of trophozoites, a primary cell enclosing a secondary cell, was detected in the epithelial cell of the renal tubule and urinary tube. Division of the parasite was followed by division of the infected epithelial cell, and the tubule became gradually swollen. In November to December, the size of enlarged kidney reached a maximum. The parasite developed to a multicellular plasmodium, in which tertiary and quartenery cells were differentiated, whereas the primary cell was disintegrated. In January to February, the plasmodium was released to the lumen, and kept growing and developing there, and the sporoblast was differentiated in the tertiary cell. In April, spores matured in the tertiary cells, which were ruptured to release the spores into the lumen. Even at this stage, young and immature trophozoites were still observed in the host epithelial cells.
Chemotherapy with fumagillin (antibiotic) and toltrazuril (sym. triazinone) was tested against kidney enlargement disease (KED) of goldfish, caused by the myxosporean Hoferellus carassii. In October, goldfish naturally infected with an early stage of H. carassii were fed daily medicated diets of fumagillin or toltrazuril. After 1 month, fish treated with fumagillin-0.1% or 1.0% diets never developed KED, and the prevalence of infection significantly decreased. In contrast, toltrazuril was not effective to KED. In November and January, fish with a gross sign of KED harbouring more advanced stages of H. carassii were also treated with fumagillin. Light and electromicroscopy revealed fumagillin caused fatal damages to developmental stages of H. carassii. Moreover, the infected epitherial cells were dead and fallen into the lumen, and only the basement membrane remained in the tubule after 1 to 2 weeks of treatment. Taking the seasonal development of the parasite into cosideration, an effective chemotherapy against KED is proposed.
A cell line from rainbow trout (Oncorhynchus mykiss) with phagocytic-like characteristics was established. First we found that it was necessary to inject the fish with antibiotics (penicillinstreptomycin) in order to clear tissue of bacterial contamination. Two days later, the spleen was excised and minced with scissors in MEM10. The large number of erythrocytes in the suspension were removed by low centrifugation, then the tissue fragments were incubated on tissue culture flasks at 18°C for 30 days with complete changes of media every other day. After 30 days in culture, primary explants from spleen were composed of three types of cells. The majority were large mononucleate, plecmorphic cells with thinly spread cytoplasm. These cells were trypsinized and subcultured. Another cell types was simple, round cells, somewhat similar to mature lymphocytes, while the third type appeared to be similar to fibroblastic cells. After 9 months with the culture in 17 to 20 passages, the predominate cell type was showing similarities to phagocytic cell. These cells had a marked reticular cytoplasm and grew individually without parallel orientations. By enzyme-specific stains, the cells were observed to have abundant acid phosphatase and β-glucuronidase activities of the cytoplasm. They were negative for peroxidase. The cells were also found to have highly adherent and phagocytic properties when incubated with latex particles. The morphological, enzymatic, and functional findings suggested the possibility that these cells in culture have some properties similar to the cells which are composed of reticulo-endothelial system.