Rethinking our understanding of the pathogenesis of necrotic enteritis in chickens

For decades, low doses of antibiotics have been used widely in animal production to promote growth. However, there is a trend to reduce this use of antibiotics in feedstuffs, and legislation is now in place in Europe to prohibit their use in this way. As a consequence, economically important diseases, such as necrotic enteritis (NE) of chickens, that are caused by Clostridium perfringens have become more prevalent. Recent research is creating a paradigm shift in our understanding of the pathogenesis of NE and is now providing information that will be necessary to monitor and control the incidence of NE in poultry

Association between avian necrotic enteritis and Clostridium perfringens strains expressing NetB toxin

A novel toxin, NetB, has recently been identified in virulent avian Clostridium perfringens isolates and shown to be an essential virulence factor in a clinical necrotic enteritis isolate. To assess whether NetB is more generally associated with avian necrotic enteritis isolates we have screened a range of C. perfringens strains from geographically diverse locations for both the presence and expression of the netB gene. Forty-four isolates were derived from necrotic enteritis disease cases from Australia, Belgium, Denmark and Canada and 55 isolates from healthy chickens from Australia and Belgium. The majority of strains isolated from necrotic enteritis-affected birds were netB positive (70%) and there was an absolute correlation between the presence of netB and in vitro expression of the NetB protein. Only two of the C. perfringens isolates from healthy chickens carried netB. Sequencing of the netB gene from 23 positive isolates showed that NetB is highly conserved, with only one predicted amino acid (A168T) difference, in six isolates, compared to the published sequence. This change did not alter the in vitro activity of the NetB toxin. The gene encoding the recently discovered TpeL toxin was also screened using PCR and only found in a small proportion of NetB-positive isolates from diseased birds. A selection of NetB-negative isolates, originating from diseased birds, was unable to cause disease in a necrotic enteritis induction model. This study provides further evidence that NetB is important in pathogenesis and advances our current understanding of C. perfringens virulence factors in avian necrotic enteritis

BBN and the Primordial Abundances

The relic abundances of the light elements synthesized during the first few minutes of the evolution of the Universe provide unique probes of cosmology and the building blocks for stellar and galactic chemical evolution, while also enabling constraints on the baryon (nucleon) density and on models of particle physics beyond the standard model. Recent WMAP analyses of the CBR temperature fluctuation spectrum, combined with other, relevant, observational data, has yielded very tight constraints on the baryon density, permitting a detailed, quantitative confrontation of the predictions of Big Bang Nucleosynthesis with the post-BBN abundances inferred from observational data. The current status of this comparison is presented, with an emphasis on the challenges to astronomy, astrophysics, particle physics, and cosmology it identifies.Comment: To appear in the Proceedings of the ESO/Arcetri Workshop on "Chemical Abundances and Mixing in Stars in the Milky Way and its Satellites", eds., L. Pasquini and S. Randich (Springer-Verlag Series, "ESO Astrophysics Symposia"

IRFM T_eff calibrations for cluster and field giants in the Vilnius, Geneva, RI(C) and DDO photometric systems

Based on a large sample of disk and halo giant stars, for which accurate effective temperatures derived through the InfraRed Flux Method (IRFM) exist, a calibration of the temperature scale in the Vilnius, Geneva, RI(C) and DDO photometric systems is performed. We provide calibration formulae for the metallicity dependent T_eff vs color relations as well as grids of intrinsic colors and compare them with other calibrations. Photometry, atmospheric parameters and reddening corrections for the stars of the sample have been updated with respect to the original sources in order to reduce the dispersion of the fits. Application of our results to Arcturus leads to an effective temperature in excellent agreement with the value derived from its angular diameter and integrated flux. The effects of gravity on these T_eff vs color relations are also explored by taking into account our previous results for dwarf stars.Comment: Accepted for publication in A&

NetB, a New Toxin That Is Associated with Avian Necrotic Enteritis Caused by Clostridium perfringens

For over 30 years a phospholipase C enzyme called alpha-toxin was thought to be the key virulence factor in necrotic enteritis caused by Clostridium perfringens. However, using a gene knockout mutant we have recently shown that alpha-toxin is not essential for pathogenesis. We have now discovered a key virulence determinant. A novel toxin (NetB) was identified in a C. perfringens strain isolated from a chicken suffering from necrotic enteritis (NE). The toxin displayed limited amino acid sequence similarity to several pore forming toxins including beta-toxin from C. perfringens (38% identity) and alpha-toxin from Staphylococcus aureus (31% identity). NetB was only identified in C. perfringens type A strains isolated from chickens suffering NE. Both purified native NetB and recombinant NetB displayed cytotoxic activity against the chicken leghorn male hepatoma cell line LMH; inducing cell rounding and lysis. To determine the role of NetB in NE a netB mutant of a virulent C. perfringens chicken isolate was constructed by homologous recombination, and its virulence assessed in a chicken disease model. The netB mutant was unable to cause disease whereas the wild-type parent strain and the netB mutant complemented with a wild-type netB gene caused significant levels of NE. These data show unequivocally that in this isolate a functional NetB toxin is critical for the ability of C. perfringens to cause NE in chickens. This novel toxin is the first definitive virulence factor to be identified in avian C. perfringens strains capable of causing NE. Furthermore, the netB mutant is the first rationally attenuated strain obtained in an NE-causing isolate of C. perfringens; as such it has considerable vaccine potential

Age and Abundance Discrimination in Old Stellar Populations Using Mid-Ultraviolet Colors

The restframe mid-ultraviolet spectral region (2000-3200 A) is important in analyzing the stellar populations of the "red envelope" systems observed at high redshifts. Here, we explore the usefulness of the mid-UV for determining ages and abundances of old populations. A mid-UV to optical/IR wavelength baseline provides good separation of population components because the main sequence turnoff dominates the integrated light between 2500 and 4000 A. We find a six magnitude difference in the mid-UV continuum level over the metallicity range -1.5 < log Z/Z_o < +0.5 and a comparable difference (per unit log t) for ages in the range 4-16 Gyr. Logarithmic derivatives of mid-UV colors with respect to age or metal abundance are 3-10 times larger than for the UBV region. Most of the spectral information on old populations therefore resides below 4000 A. We investigate the capability of UBV and mid-UV broad-band colors to separately determine age and abundance, taking into account precision in the color measurements. We find that the mid-UV improves resolution in (log t,log Z) space by about a factor of 3 for a given observational precision. Contamination by hot horizontal branch phases can seriously affect mid-UV spectra, reaching over 80% in some cases. However, this is straightforward to remove as long as far-UV measurements are available. Finally, we show that a 4 Gyr, solar abundance model based on empirical spectra provides an excellent fit to the mid-UV spectrum of the E galaxy M32. This indicates that the poorer results obtained from theoretical spectra arise from limitations of the synthesis models for individual stars. [Condensed]Comment: 38 pages, 8 figures. Accepted by ApJ. Full resolution figures available at: http://www.astro.virginia.edu/~rwo/miduv-fullresfigs.ps.g

The Luminosity Function of M3

We present a high precision, large sample luminosity function (LF) for the Galactic globular cluster M3. With a combination of ground based and Hubble Space Telescope data we cover the entire radial extent of the cluster. The observed LF is well fit by canonical standard stellar models from the red giant branch (RGB) tip to below the main sequence turnoff point. Specifically, neither the RGB LF-bump nor subgiant branch LF indicate any breakdown in the standard models. On the main sequence we find evidence for a flat initial mass function and for mass segregation due to the dynamical evolution of the cluster.Comment: 18 pages, 13 figures. ApJ, in pres

Association between stringency of lockdown measures and emergency department visits during the COVID-19 pandemic:A Dutch multicentre study

Introduction The COVID-19 outbreak disrupted regular health care, including the Emergency Department (ED), and resulted in insufficient ICU capacity. Lockdown measures were taken to prevent disease spread and hospital overcrowding. Little is known about the relationship of stringency of lockdown measures on ED utilization. Objective This study aimed to compare the frequency and characteristics of ED visits during the COVID-19 outbreak in 2020 to 2019, and their relation to stringency of lockdown measures. Material and methods A retrospective multicentre study among five Dutch hospitals was performed. The primary outcome was the absolute number of ED visits (year 2018 and 2019 compared to 2020). Secondary outcomes were age, sex, triage category, way of transportation, referral, disposition, and treating medical specialty. The relation between stringency of lockdown measures, measured with the Oxford Stringency Index (OSI) and number and characteristics of ED visits was analysed. Results The total number of ED visits in the five hospitals in 2019 was 165,894, whereas the total number of visits in 2020 was 135,762, which was a decrease of 18.2% (range per hospital: 10.5%-30.7%). The reduction in ED visits was greater during periods of high stringency lockdown measures, as indicated by OSI. Conclusion The number of ED visits in the Netherlands has significantly dropped during the first year of the COVID-19 pandemic, with a clear association between decreasing ED visits and increasing lockdown measures. The OSI could be used as an indicator in the management of ED visits during a future pandemic.</p