European freshwater VHSV genotype Ia isolates divide into two distinct subpopulations.

Viral haemorrhagic septicaemia (VHS), caused by the novirhabdovirus VHSV, often leads to significant economic losses to European rainbow trout production. The virus isolates are divided into 4 distinct genotypes with additional subgroups including sublineage Ia, isolates of which are the main source of outbreaks in European rainbow trout farming. A significant portion of Danish rainbow trout farms have been considered endemically infected with VHSV since the first disease outbreak was observed in the 1950s. However, following a series of sanitary programs starting in 1965, VHSV has not been detected in Denmark since January 2009. Full-length G-genes of all Danish VHSV isolates that were submitted for diagnostic analyses in the period 2004-2009 were sequenced and analysed. All 58 Danish isolates from rainbow trout grouped with sublineage Ia isolates. Furthermore, VHSV isolates from infected Danish freshwater catchments appear to have evolved into a distinct clade within sublineage Ia, herein designated clade Ia-1, whereas trout isolates originating from other continental European countries cluster in another distinct clade, designated clade Ia-2. In addition, phylogenetic analyses indicate that VHSV Ia-1 strains have caused a few outbreaks in Germany and the UK. It is likely that viruses have been transmitted from infected site(s) out of the Danish environment, although a direct transmission pathway has not been identified. Furthermore, VHSV Ia-2 isolates seem to have been transmitted to Denmark at least once. Interestingly, one viral isolate possibly persisted in a Danish watershed for nearly 4 yr without detection whereas other subclades of VHSV isolates appear to have been eliminated, probably because of implemented eradication procedures.

The first report of viral haemorrhagic septicaemia in farmed rainbow trout, Oncorhynchus mykiss (Walbaum), in the United Kingdom.

Viral haemorrhagic septicaemia (VHS) was diagnosed in rainbow trout in the UK in May 2006. VHS virus (VHSV) was isolated from fingerlings showing typical histopathological lesions at a single rainbow trout farm site experiencing high mortality. The virus was confirmed as VHSV by serological and molecular biological tests. Phylogenetic analysis based on the complete glycoprotein gene sequence revealed that the isolate was closely related (99% nucleotide identity) to several Danish isolates from 1991 to 2000 and was assigned to VHSV genogroup Ia. The pathogenicity of the isolate was determined in infection experiments using rainbow trout fry. Following waterborne challenge, cumulative mortalities reached 96.67-100% by 12 days post-infection. This represents the first isolation of a pathogenic freshwater VHSV in the UK.

Optical and Mechanical Properties of Some Neodymium-Doped Laser Glasses.

Studies have been made to evaluate thermo-optic and piezo-optic properties of five laser glasses. Measurements were made at the Cd red line, λ = 0.6438 µm, over a wide range of temperatures and pressures using interferometric and polarimetric techniques. The refractive index-temperature data show both positive and negative values and small changes with temperature. The changes in index with applied compressive stress are positive in value. Other optical properties evaluated were homogeneity, transmittance, and refractive index as a function of wavelength. An ultrasonic pulse-echo technique was used to determine the elastic constants, Young's modulus, shear modulus, bulk modulus, and Poisson's ratio. Data for thermal expansion, thermal conductivity, density, hardness and chemical composition are also given. Calculations were made of the thermal change of refractive index at constant volume. These data can be used to calculate corrections for the distortions of the wavefront of light generated in lasers.

A special method for precise refractive index measurement of uniaxial optical media.

A method was developed for measuring the refractive index of optical glasses and uniaxial crystalline solids when established refractometric methods are not feasible. A synthetic ruby cuboid was contacted to a prism of known refractive index and a spectrometer was used to measure the angles describing the optical path through the ruby-glass combination. Ray tracing equations were derived to compute the refractive index accurate within 3 x 10(-5). Index values for both polarizations of ruby are given at selected wavelengths from 0.4358 microm to 0.7065 microm.