Nikolaos Demiris

Influence of organic selenium supplementation on the accumulation of toxic and essential trace elements involved in the antioxidant system of chicken.

The aim of the study was to investigate the interactions between selenium (Se) and various trace elements, both toxic and essential, involved in the antioxidant system. A total of 128 day-old chicks (Gallus gallus, broilers) were used to investigate the effect of Se yeast supplementation on the accumulation of cadmium (Cd), copper (Cu) iron (Fe) and zinc (Zn). There were four replicates of four dietary treatments: T1 (basal diet with no added Se, analyzed to contain 0.21 mg kg−1), T2 (T1 with 0.15 mg kg−1 Se added), T3 (T1 with 0.3 mg kg−1 Se) and T4 (T1 with 3.0 mg kg−1 Se). At week 4 and 6, two chickens per replicate pen were sacrificed for whole blood, breast muscle and liver sampling. Samples were analyzed by ICP–MS. Supplementation with Se-yeast, not only increased Se concentration but also reduced Cd concentration in the tissues. Selenium was negatively correlated with Cd and positively correlated with Zn, Cu and Fe. Cadmium was negatively correlated with Zn and Cu. Zinc was positively correlated with Cu. Iron was negatively correlated with Cu and uncorrelated with Zn and Cd. The balance between Se, Cu, Fe and Zn is important for proper antioxidant defense since they are an integral part of various antioxidant enzymes.

Microsimulation and clinical outcomes analysis support a lower age threshold for use of biological valves

Objective To characterise contemporary results of aortic valve replacement in relation to type of prosthesis and subsequent competing hazards. Methods 5470 procedures in 5433 consecutive patients with aortic valve replacement ± coronary artery bypass grafting (CABG) were studied. Microsimulation of survival and valve-related outcomes was performed based on meta-analysis and patient data inputs, with separate models for age, gender and CABG. Survival was validated against the UK Heart Valve Registry. Results Patient survival at 1, 5 and 10 years was 90%, 78% and 57%, respectively. The crossover points at which bioprostheses and mechanical prostheses conferred similar life expectancy (LE) was 59 years for men and women (no significant difference between prosthesis types between the ages of 56 and 69 for men, and 58 an 63 for women). The improvement in event-free LE for mechanical valves was greater at younger ages with a crossover point of 66 years for men and 67 years for women. Long-term survival was independently influenced by age, male gender and concomitant CABG, but not by type of prosthesis. In bioprostheses the most common long-term occurrence was structural deterioration. For men aged 55, 65 and 75 at initial operation it had a lifetime incidence of 50%, 30% and 13%, respectively. The simulation output showed excellent agreement with registry data. Conclusion Bioprostheses can be implanted selectively in patients as young as 56 without significant adverse effects on life expectancy, although event-free life expectancy remains significantly lower with bioprostheses up to age of implant of 63.

Computation of final outcome probabilities for the generalised stochastic epidemic

This paper is concerned with methods for the numerical calculation of the final outcome distribution for a well-known stochastic epidemic model in a closed population. The model is of the SIR (Susceptible→Infected→ Removed) type, and the infectious period can have any specified distribution. The final outcome distribution is specified by the solution of a triangular system of linear equations, but the form of the distribution leads to inherent numerical problems in the solution. Here we employ multiple precision arithmetic to surmount these problems. As applications of our methodology, we assess the accuracy of two approximations that are frequently used in practice, namely an approximation for the probability of an epidemic occurring, and a Gaussian approximation to the final number infected in the event of an outbreak. We also present an example of Bayesian inference for the epidemic threshold parameter.

Life-years gained by reducing donor heart ischemic times

Background. Transplantation is limited by the number of available donor organs. Donor organ maintenance systems are a recent technological advance. These systems may increase the number of donor organs that can be used and improve outcomes by decreasing donor organ ischemic time (IT). The purpose of this study was to determine the potential life-years gained if IT in the United Kingdom were decreased for cardiac transplantation. Methods. Proportional hazards regression and extrapolation of survival rates beyond 20 years posttransplantation were used to estimate the effect of decreasing total IT on survival and the life-years gained over the lifetime of UK heart transplantation patients. Results. Median survival posttransplantation was 10.4 years (95% CI 9.9 to 10.9). For each additional hour of donor organ IT, patients had a 25% increased risk of death after heart transplantation in the first year after transplant, with a 5% increase thereafter (P<0.001). On average, a recipient surviving 10 years posttransplantation could potentially gain 0.4 (95% CI 0.1 to 0.7) life-years if IT was reduced to 1 hr. The longer the IT, the greater the potential life-years to gain; for example, a recipient of an organ that would have had an IT of 6 hr without the use of an organ maintenance system might expect to gain 2.9 life-years (95% CI −0.6 to 6.4) if IT was reduced to 1 hr. Conclusions. Use of cardiac donor organ maintenance systems has the potential to increase posttransplantation survival.

Survival extrapolation using the poly-Weibull model

Recent studies of (cost-) effectiveness in cardiothoracic transplantation have required estimation of mean survival over the lifetime of the recipients. In order to calculate mean survival, the complete survivor curve is required but is often not fully observed, so that survival extrapolation is necessary. After transplantation, the hazard function is bathtub-shaped, reflecting latent competing risks which operate additively in overlapping time periods. The poly-Weibull distribution is a flexible parametric model that may be used to extrapolate survival and has a natural competing risks interpretation. In addition, treatment effects and subgroups can be modelled separately for each component of risk. We describe the model and develop inference procedures using freely available software. The methods are applied to two problems from cardiothoracic transplantation.

Assessing the Benefit of Accepting a Single Lung Offer Now Compared With Waiting for a Subsequent Double Lung Offer

Background. Comparisons of survival after single lung transplant (SLT) and bilateral lung transplant (BLT) are useful in making policy decisions, but a more relevant comparison for an individual patient is between accepting a single lung when offered and remaining on the waiting list with the potential to subsequently receive a suitable pair of lungs. Methods. U.K. data from a cohort of 1211 adult, first lung transplant candidates diagnosed with pulmonary fibrosis (PF) or chronic obstructive pulmonary disease (COPD), listed July 1995 to July 2006 and followed up till December 2007, were analyzed. A sequentially stratified proportional hazards model was used to assess mortality after SLT relative to continued waiting for BLT. Results. For patients with PF, SLT was associated with a significant reduction in hazard relative to waiting for BLT (hazard ratio 0.81, 95% confidence interval 0.68–0.97, P=0.021), particularly for older patients with body mass index less than 20 and forced expired volume in 1 sec is less than 1 L. In contrast, our results gave no support for accepting SLT rather than waiting for BLT for patients with COPD (hazard ratio 1.08, 95% confidence interval 0.92–1.29, P=0.35). Conclusion. The high pretransplant risk of death for patients with PF, particularly older patients with low body mass index and poor lung function, suggests that they would benefit from taking an SLT if offered. However, there is no benefit of accepting SLT rather than waiting for BLT for patients with COPD; this reflects the low relative hazard in the absence of transplant for these patients.

Meta-analysis of selenium accumulation and expression of antioxidant enzymes in chicken tissues

A meta-analysis integrating results of 40 selenium (Se) supplementation experiments that originated from 35 different controlled randomized trials was carried out in an attempt to identify significant factors that affect tissue Se accumulation in chicken. Examined factors included: Se source (12 different sources examined), type of chicken (laying hens or broilers), age of birds at the beginning of supplementation, duration of supplementation, year during which the study was conducted, sex of birds, number of chickens per treatment, method of analysis, tissue type, concentration of Se determined and Se added to feed. A correlation analysis was also carried out between tissue Se concentration and glutathione peroxidase activity. Data analysis showed that the factors significantly affecting tissue Se concentration include type of chicken (P=0.006), type of tissue (P<0.001) and the analytical method used (P=0.014). Although Se source was not found to affect tissue Se concentration (overall P>0.05), certain inorganic (sodium selenite), calcium selenite, sodium selenate and organic sources (B-Traxim Se), Se-yeast, Se-malt, Se-enriched cabbage and Se-enriched garlic as well as background Se level from feed ingredients were found to significantly affect tissue Se concentration. The Se accumulation rate (estimated as linear regression coefficient of Se concentrations to Se added to feed) discriminated between the various tissues with highest values estimated in the leg muscle and lowest in blood plasma. Correlation analysis has also shown that tissue Se concentration (pooled data) was correlated to Se added to feed (r=0.529, P<0.01, log values) and to glutathione peroxidase activity (r=0.332, P=0.0478), with the latter not being correlated with Se added to feed. Although significant factors affecting Se concentration were reported in the present study, they do not necessarily indicate the in vivo function of the antioxidant system or the level of accumulated Se as other factors, not examined in the present study, may interact at the level of trace element absorption, distribution and retention.

Modeling sheep pox disease from the 1994-1998 epidemic in Evros Prefecture, Greece.

Sheep pox is a highly transmissible disease which can cause serious loss of livestock and can therefore have major economic impact. We present data from sheep pox epidemics which occurred between 1994 and 1998. The data include weekly records of infected farms as well as a number of covariates. We implement Bayesian stochastic regression models which, in addition to various explanatory variables like seasonal and environmental/meteorological factors, also contain serial correlation structure based on variants of the Ornstein-Uhlenbeck process. We take a predictive view in model selection by utilizing deviance-based measures. The results indicate that seasonality and the number of infected farms are important predictors for sheep pox incidence.

Evaluating the frequency of asymptomatic Ebola virus infection.

The potential for asymptomatic infection from Ebola viruses has long been questioned. Knowing the proportion of infections that are asymptomatic substantially changes the predictions made by mathematical models and alters the corresponding decisions based upon these models. To assess the degree of asymptomatic infection occurring during an Ebola virus disease (EVD) outbreak, we carried out a serological survey in the Djera district of the Equateur province of the Democratic Republic of the Congo affected by an Ebola outbreak in 2014. We sampled all asymptomatic residents (n = 182) of 48 households where at least one case of EVD was detected. To control for potential background seroprevalence of Ebola antibodies in the population, we also sampled 188 individuals from 92 households in an unaffected area with a similar demographic background. We tested the sera collected for anti-Ebola IgG and IgM antibodies at four different dilutions. We then developed a mixture model to estimate the likely number of asymptomatic patients who developed IgM and IgG responses to Ebola antigens in both groups. While we detected an association between medium to high titres and age, we did not detect any evidence of increased asymptomatic infection in the individuals who resided in the same household as cases. This article is part of the themed issue ‘The 2013–2016 West African Ebola epidemic: data, decision-making and disease control’.

An early warning indicator for monitoring infectious animal diseases and its application in the case of a sheep pox epidemic

We describe an early warning indicator for monitoring infectious diseases. The approach is illustrated with data from a major sheep pox epidemic, which occurred in the Evros prefecture of Greece, from August 2013 until the end of 2014. We present the epidemic data and identify factors affecting this major epidemic using a suitable methodological framework for the sequential analysis of such outbreaks. Environmental conditions and seasonality affect the spread of the epidemic: autumn seems to enhance disease occurrence and higher average temperatures facilitate disease spread. The on-line prediction of the disease potential is investigated through an early warning system that is based on the probability of the disease going extinct. The temporal stability of this indicator is extensively explored.