The relationship between porcine circovirus 2 antigen score and antibody titre and histology of lymph nodes in 375 euthanased sick and healthy pigs from 113 British pig farms with and without postweaning multisystemic wasting syndrome.

Data from a cross-sectional study of 113 British pig herds carried out in 2004 were used to investigate the associations between postweaning multisystemic wasting (PMWS) in pigs and herds and porcine circovirus 2 (PCV2) antigen score and antibody titre, and associated histological signs in lymph nodes. The sensitivity and specificity of published herd definitions for PMWS were tested on the study farms to consider the role of PCV2 in PMWS. Herds were defined as PMWS-affected, -unaffected or -recovered based on current and past postweaning mortality (PWM), grower pigs with clinical signs of rapid wasting, hairiness and pallor and no other known cause of death on the farm. PCV2 antigen and antibody were not used in the definition of PMWS. In each PMWS-affected herd, up to three sick pigs with the clinical signs above and one healthy pig of a similar age were taken for postmortem examination (PME). In all other herds at least one healthy pig was taken for PME. Lymph nodes were analysed for PCV2 antigen and histological changes, and serum samples were analysed for PCV2 antibody. PCV2 antibody was present in all the herds sampled. There was a non-linear association between PCV2 antigen and antibody. There was no association between the presence of high scores of PCV2 antigen in pigs and the presence of high PWM in herds. PCV2 antigen score was significantly higher in sick than healthy pigs within farms, and high PCV2 score was associated with giant cells, coalescence and absence of germinal centres in lymph nodes. These results did not vary by PMWS-affected, -unaffected or -recovered farms. PCV2 antigen was present at high scores in approximately 10% of healthy pigs on all farms. All three herd definitions of PMWS were highly sensitive, defining PMWS-affected herds as affected, but had a specificity ranging from 23% to 43%. We conclude that the current diagnostic tests for PCV2 indicated higher scores of virus in sick pigs but were not useful to define pigs or herds with PMWS. The ubiquity of PCV2 and the lack of specificity of the PCV2 tests indicate that PCV2 may be a necessary but not sufficient cause of PMWS disease. Linking this with the knowledge that the herd breakdowns occurred in a space time epidemic indicates that another infectious co-factor may be necessary for disease to occur.

Wavelength-dependent collective effects in the multiphoton ionization of atomic deuterium.

This paper presents the results of an experimental investigation into collective effects in the transient plasma formed by multiphoton ionization of atomic deuterium with a pulsed laser. The laser wavelength is varied in a narrow range around 243 nm, so that the photoionization is resonant with the metastable 2S(1/2) state. The ion yield, the ion time-of-flight spectra, and the yield of Lyman-alpha photons have been measured as a function of laser intensity (from 1 to 340 MW/cm(2)) and laser detuning around the 1S(1/2)-2S(1/2) two-photon resonance. During and shortly after the laser pulse, collective effects resulting from the mutual interaction of the photoelectrons and the ions affect the spatial and temporal distribution of the ions. Because of the near-degeneracy of the 2S(1/2), 2P(1/2), and 2P(3/2) states, the resonant multiphoton ionization is affected by the Stark mixing of these states in the collective field. As a result, the time-dependent yields of ions and of Lyman-alpha photons are modulated by the interplay of the multiphoton ionization of the atoms and the collective effects in the plasma. From the measurements it is deduced that collective effects are important above a critical charge density of 3x10(8) ions/cm(3). An asymmetry is observed in the line profile of the total ion yield as a function of laser detuning. This asymmetry is interpreted to be due to the effect of the collective field upon the intermediate resonant 2S(1/2) state of the photoionization process.

Holographic evaluation of ceramic materials.

The coherent optical technique of holographic correlation is applied to the nondestructive evaluation of ceramic materials. A Fresnel correlator is used to holographically construct a matched filter to a small test area on the surface of a silicon nitride ceramic. The subsequent change in correlation signal intensity, from localized microstructural changes occurring on the ceramic surface, is determined as the sample is subjected to thermal stress. A novel method to detect and quantify any loss in correlation signal strength arising from the bulk movement of the ceramic sample within its support is described. Results are presented which show that the correlation technique is capable of evaluating the characteristics of ceramic materials in terms of their response to thermal stress.