Diversity of Flavobacterium psychrophilum and the potential use of its phages for protection against bacterial cold water disease in salmonids

Flavobacterium psychrophilum causes rainbow trout fry syndrome (RTFS) and cold water disease (CWD) in salmonid aquaculture. We report characterization of F. psychrophilum strains and their bacteriophages isolated in Chilean salmonid aquaculture. Results suggest that under laboratory conditions phages can decrease mortality of salmonids from infection by their F. psychrophilum host strain. Twelve F. psychrophilum isolates were characterized, with DNA restriction patterns showing low diversity between strains despite their being obtained from different salmonid production sites and from different tissues. We isolated 15 bacteriophages able to infect some of the F. psychrophilum isolates and characterized six of them in detail. DNA genome sizes were close to 50 Kbp and corresponded to the Siphoviridae and Podoviridae families. One isolate, 6H, probably contains lipids as an essential virion component, based on its chloroform sensitivity and low buoyant density in CsCl. Each phage isolate rarely infected F. psychrophilum strains other than the strain used for its enrichment and isolation. Some bacteriophages could decrease mortality from intraperitoneal injection of its host strain when added together with the bacteria in a ratio of 10 plaque-forming units per colony-forming unit. While we recognize the artificial laboratory conditions used for these protection assays, this work is the first to demonstrate that phages might be able protect salmonids from RTFS or CWD.     

Flavobacterium psychrophilum in rainbow trout, Oncorhynchus mykiss (Walbaum), hatcheries: studies on broodstock, eggs, fry and environment

The occurrence of Flavobacterium psychrophilum at four rainbow trout hatcheries was investigated to provide more knowledge about the reservoirs and transmission of this bacterium. Broodstock were sampled at stripping (including both unfertilized and fertilized eggs), and the offspring were then sampled at the eyed egg and fry stages. Water and surface samples (e.g. hatchery trays) were also sampled. Flavobacterium psychrophilum was found in ovarian fluid and milt, indicating that broodstock may serve as a reservoir and are latent carriers of the pathogen. Flavobacterium psychrophilum was not found on or inside eggs, but further egg studies will be necessary to elucidate the possibility of vertical transmission of the pathogen. Flavobacterium psychrophilum was isolated from water samples, but only from water that had been in close contact with farmed rainbow trout or eggs. Flavobacterium psychrophilum isolates were characterized and compared with well-characterized strains, using degradation of elastin, serotype and ribotype profiles. Different ribotypes of F. psychrophilum were found between hatcheries, but a common ribotype A was found at all four hatcheries. Different ribotypes were found in broodstock without clinical disease, whereas only a few ribotypes (mostly ribotype A) were found in diseased fry. The same ribotype A was found in broodstock, in water samples from hatchery trays and in fry, which suggests the possibility of transmission of F. psychrophilum between broodstock and offspring.     

Field assessment of partial resistance to powdery mildew in spring barley

Summary Partial resistance to powdery mildew in spring barley was evaluated in three plot types: large isolation plots, in 1.4 m² plots in chessboard design with guard plots of spring wheat and in single rows. Percentage leaf area covered by powdery mildew was scored four to six times during the season and partial resistance was characterized by the area under the disease progress curve. Varietal differences were revealed in al three plot designs, differences between the most resistant and susceptible genotypes being of a factor five. Differences between varieties decreased with decreasing plot size. The relationship between single scores of amount of powdery mildew on the upper four leaves and the area under the disease progress curve was high in all plot designs during the first two to three weeks after heading, allowing selection for the trait by one or two scorings. Differential ranking of varieties between different plot designs was observed, and is assumed to be due to increasing plot interference with reduced plot size and reduced distance between plots. A reliable selection for partial resistance could be made in large isolation plots and in 1.4 m² plots, but hardly in single rows.     

Rapid method for screening of immunoglobulins in porcine fetuses, using rocket immunoelectrophoresis. Application of an interspecies reaction between human and porcine mu-chain

A method for screening of immunoglobulin levels in porcine fetuses is presented. The method is based on rocket electrophoresis. This method is sensitive, but when used for assaying immunoglobulins it is only semiquantitative. It was shown that sera from 11 hysterectomy-derived colostrum-deprived neonatal pigs from a normal gilt contained no IgM or IgA, but small amounts of IgG. Sera from 9 piglets isolated in the same way from a gilt infected with porcine parvovirus contained all 3 antibody classes. IgM was detected by an interspecies reaction using anti human μ-chain immunoglobulin.     

Experimental fetal infection with bovine viral diarrhea virus. I. Virological and serological studies.

The serological and virological results of an experimental infection of bovine fetuses with bovine viral diarrhea virus are presented. Four fetuses, 120-165 days gestational age, were inoculated in utero with a second passage virus strain. Two fetuses received a sham-inoculum. A humoral immune response in the virus-inoculated fetuses, was demonstrated three weeks later. In three fetuses only IgM and IgG1 were detectable. The serum from the fourth fetus also contained IgG2 and IgA. Bovine viral diarrhea virus-neutralizing antibodies were detected in two fetuses. These two fetuses inoculated at 135-150 days gestational age, represent the youngest reported bovids, giving a specific response in three weeks following an experimental infection with bovine viral diarrhea virus. The fetal sera did not contain heat-labile factors, which could mediate the neutralization. The virus was not reisolated from any of the fetuses, but viral antigen was nevertheless demonstrated by immunocytochemical methods in sections of several of the fetal organs, primarily lymphoid tissues.     

The effect of ignoring individual heterogeneity in Weibull log-normal sire frailty models

The objective of this study was, by means of simulation, to quantify the effect of ignoring individual heterogeneity in Weibull sire frailty models on parameter estimates and to address the consequences for genetic inferences. Three simulation studies were evaluated, which included 3 levels of individual heterogeneity combined with 4 levels of censoring (0, 25, 50, or 75%). Data were simulated according to balanced half-sib designs using Weibull log-normal animal frailty models with a normally distributed residual effect on the log-frailty scale. The 12 data sets were analyzed with 2 models: the sire model, equivalent to the animal model used to generate the data (complete sire model), and a corresponding model in which individual heterogeneity in log-frailty was neglected (incomplete sire model). Parameter estimates were obtained from a Bayesian analysis using Gibbs sampling, and also from the software Survival Kit for the incomplete sire model. For the incomplete sire model, the Monte Carlo and Survival Kit parameter estimates were similar. This study established that when unobserved individual heterogeneity was ignored, the parameter estimates that included sire effects were biased toward zero by an amount that depended in magnitude on the level of censoring and the size of the ignored individual heterogeneity. Despite the biased parameter estimates, the ranking of sires, measured by the rank correlations between true and estimated sire effects, was unaffected. In comparison, parameter estimates obtained using complete sire models were consistent with the true values used to simulate the data. Thus, in this study, several issues of concern were demonstrated for the incomplete sire model.