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Streptococcus iniae is a major pathogen of fish, producing fatal disease among fish species living in very diverse environments. Recently, reoccurrences of disease outbreaks were recorded in rainbow trout (Oncorhynchus mykiss, Walbaum) farms where the entire fish population was routinely vaccinated. New strains are distinguished from previous strains by their ability to produce large amounts of extracellular polysaccharide that is released into the medium. Present findings indicate that the extracellular polysaccharide is a major antigenic factor, suggesting an evolutionary selection of strains capable of extracellular polysaccharide production.

Clinical and pathological findings (anorexia, hemorrhage, lethargy, loss of orientation and exophthalmia) indicated that Streptococcus iniae type II is responsible for a fatal disease in rainbow trout. Histopathological findings revealed that S. iniae type II produces a systemic disease, including a diffuse necrotizing myositis. The distribution of viable bacteria in infected tissues substantiated the pathological findings, confirming that S. iniae type II is responsible for a generalized septic disease of rainbow trout. KEY WORDS: Rainbow trout · Streptococcus iniae · Serotype · Pathology Resale or republication not permitted without written consent of the publisherDis Aquat Org 62: [177][178][179][180] 2004 2003). In the present work we assessed the pathological outcomes of infections of rainbow trout by S. iniae serotype II. Our results indicate that Serotype II strains produce an acute septic disease accompanied by multisystem organ involvement. MATERIALS AND METHODSSampling procedure for pathology and bacteriological analysis. Specimens were collected from 2 trout farms located in northern Israel (Upper Galilee) which are supplied with water at a constant temperature of 16°C. At the time of collection both farms were experiencing heavy mortalities, and bacteriological examination (30 fish from each farm, 50 to 350 g each) revealed pure colonies of β-hemolytic Gram-positive cocci. Bacteriological identification (Eldar et al. 1995), authenticated by PCR analysis (Zlotkin et al. 1998), confirmed the presence of arginine dehydrolase-negative isolates of Streptococcus iniae. PCR analysis with the p14 primer did not produce the 750 bp band, indicating that all current isolates were of type II (Bachrach et al. 2001). Tissues (brain, heart, spleen, kidney, liver, intestine, gills and muscle) from 10 diseased rainbow trout were fixed in 10% neutral buffered formalin and stained with hematoxylin and eosin (HE). Gross lesions were recorded.Distribution of bacteria in tissues. Bacterial colonyforming units (CFUs) were counted in the tissues of 20 rainbow trout (100 to 200 g each), infected with Streptococcus iniae type II and showing clinical signs of streptococcosis (darkening of the skin combined with multifocal ecchymoses, lethargy, loss of orientation and ocular pathologies). Organs (brain, heart, spleen, kidney, liver, intestine, gills and muscle) were weighed and blended over a 60-mesh grid. Tissue homogenate samples (1 g) were suspended in 10 ml phosphatebuffered saline (PBS) (15 mM Na 2 HPO 4 , 145 mM NaCl, pH 7.20) supplemented with 0.2% Triton X-100 (Sigma) and serially diluted. The bacterial CFU population was determined by plate counting.The bacterial loads in tissues of rainbow trout infected by Streptococcus iniae type I were assessed with a 2-step cohabitation method. First, 10 naive rainbow trout (50 to 80 g each) were infected by intraperitoneal inoculation of (7.5 × 10 5 CFU fish -1 ) virulent S. iniae Dan-15 (type I strain), as described previously (Eldar et al. 1997a). Then, on Day 10 ...

Streptococcus iniae is a major pathogen of fish, causing considerable economic losses in Israel, the United States and the Far East. Containment of mortalities through vaccination was recently compromised due to the emergence of novel vaccine-escape strains that are distinguished from previous strains by their ability to produce large amounts of extracellular polysaccharide (EPS) that is released to the medium. In vitro and in vivo data now indicate that the EPS is a major virulence factor, capable of triggering the proinflammatory cytokine machinery and inducing mortality of fish. Streptococcus iniae EPS might therefore be considered to be responsible for sepsis and death just as lipopolysaccharide is for Gram-negative pathogens.

Thirteen HA agents were isolated in Israel from captive flamingoes (Phoenicopterus ruber), Egyptian geese (Alopochen aegyptiacus) belonging to order Anseriformes, and ibis (Guara rubra) belonging to order Ciconiiformes. The isolation was done from postmortem materials in three cases of severe respiratory disease with high mortality. The isolates were examined serologically and identified as belonging to the serotype 3 of avian paramyxoviruses (APMV-3). The isolates were more close antigenically to the APMV-3b variety (prototype strain--APMV-3/Parakeet/Netherlands/449/75) than to the APMV-3a variety (prototype strain--APMV-3/Turkey/Wisconsin/68). This is the first isolation of APMV-3 from birds belonging to the orders Anseriformes and Ciconiiformes.