Experimental pig-to-pig transmission dynamics for African swine fever virus, Georgia 2007/1 strain

African swine fever virus (ASFV) continues to cause outbreaks in domestic pigs and wild boar in Eastern European countries. To gain insights into its transmission dynamics, we estimated the pig-to-pig basic reproduction number (R 0) for the Georgia 2007/1 ASFV strain using a stochastic susceptible-exposed-infectious-recovered (SEIR) model with parameters estimated from transmission experiments. Models showed that R 0 is 2·8 [95% confidence interval (CI) 1·3–4·8] within a pen and 1·4 (95% CI 0·6–2·4) between pens. The results furthermore suggest that ASFV genome detection in oronasal samples is an effective diagnostic tool for early detection of infection. This study provides quantitative information on transmission parameters for ASFV in domestic pigs, which are required to more effectively assess the potential impact of strategies for the control of between-farm epidemic spread in European countries.ISSN:0950-2688ISSN:1469-440

Bone intake by vultures in Namibia

The use of bones by vultures was assessed during early 2005 in the Otjiwarongo area in north-central Namibia. Bone fragments were utilized by all species, especially by the African White-backed Vulture Gyps africanus and the Lappet-faced Vulture Torgos tracheliotos. There was an overall increase in bone fragment consumption from May onwards (taken as the beginning of the breeding period). A rough estimate of bone fragment use for all vultures of 2.49 g/vulture (consumption/total number of vultures observed) and 60.31 g/vulture (consumption/individuals of vultures observed) was determined. The results suggest that bone fragments should be added as a supplement at vulture restaurants.Vulture News Vol. 57 2007: pp. 17-2

Behavior of susceptible-infected-susceptible epidemics on heterogeneous networks with saturation

We investigate saturation effects in susceptible-infected-susceptible (SIS) models of the spread of epidemics in heterogeneous populations. The structure of interactions in the population is represented by networks with connectivity distribution $P(k)$,including scale-free(SF) networks with power law distributions $P(k)\sim k^{-\gamma}$. Considering cases where the transmission of infection between nodes depends on their connectivity, we introduce a saturation function $C(k)$ which reduces the infection transmission rate $\lambda$ across an edge going from a node with high connectivity $k$. A mean field approximation with the neglect of degree-degree correlation then leads to a finite threshold $\lambda_{c}>0$ for SF networks with $2<\gamma \leq 3$. We also find, in this approximation, the fraction of infected individuals among those with degree $k$ for $\lambda$ close to $\lambda_{c}$. We investigate via computer simulation the contact process on a heterogeneous regular lattice and compare the results with those obtained from mean field theory with and without neglect of degree-degree correlations.Comment: 6 figure

Effects of aging and links removal on epidemic dynamics in scale-free networks

We study the combined effects of aging and links removal on epidemic dynamics in the Barab\'{a}si-Albert scale-free networks. The epidemic is described by a susceptible-infected-refractory (SIR) model. The aging effect of a node introduced at time $t_{i}$ is described by an aging factor of the form $(t-t_{i})^{-\beta}$ in the probability of being connected to newly added nodes in a growing network under the preferential attachment scheme based on popularity of the existing nodes. SIR dynamics is studied in networks with a fraction $1-p$ of the links removed. Extensive numerical simulations reveal that there exists a threshold $p_{c}$ such that for $p \geq p_{c}$, epidemic breaks out in the network. For $p < p_{c}$, only a local spread results. The dependence of $p_{c}$ on $\beta$ is studied in detail. The function $p_{c}(\beta)$ separates the space formed by $\beta$ and $p$ into regions corresponding to local and global spreads, respectively.Comment: 8 pages, 3 figures, revtex, corrected Ref.[11

Immunization for complex network based on the effective degree of vertex

The basic idea of many effective immunization strategies is first to rank the importance of vertices according to the degrees of vertices and then remove the vertices from highest importance to lowest until the network becomes disconnected. Here we define the effective degrees of vertex, i.e., the number of its connections linking to un-immunized nodes in current network during the immunization procedure, to rank the importance of vertex, and modify these strategies by using the effective degrees of vertices. Simulations on both the scale-free network models with various degree correlations and two real networks have revealed that the immunization strategies based on the effective degrees are often more effective than those based on the degrees in the initial network.Comment: 16 pages, 5 figure

Synthetic curved DNA sequences can act as transcriptional activators in Escherichia coli.

Can a transcriptional activator known to bend DNA be functionally replaced by a sequence-directed bend in Escherichia coli? To investigate this question, a partially truncated promoter was used, deleted of its -35 region and of its CRP binding site, leaving only two Pribnow boxes as functional elements. Synthetic and naturally occurring curved DNA sequences introduced upstream from these elements could restore transcription at either one of the two natural starts. Some of these hybrid promoters turned out to be more efficient than the CRP activated wild-type gal promoter in vivo. Control experiments performed with very similar sequences devoid of any curvature produced weak promoters only. Minimal changes in the location of the centre of curvature or perturbation in the amount of curvature strongly affected the level of expression. No significant stimulation of transcription could be detected in vitro. Furthermore, both gal P1 and P2 starts could be activated in vivo but also in vitro via a properly positioned CRP binding site. This partial analogy suggests that bending induced by the cAMP-CRP complex upon binding to its site may be biologically relevant to the mechanism of transcriptional activation

Population Dynamics in Spatially Heterogeneous Systems with Drift: the generalized contact process

We investigate the time evolution and stationary states of a stochastic, spatially discrete, population model (contact process) with spatial heterogeneity and imposed drift (wind) in one- and two-dimensions. We consider in particular a situation in which space is divided into two regions: an oasis and a desert (low and high death rates). Carrying out computer simulations we find that the population in the (quasi) stationary state will be zero, localized, or delocalized, depending on the values of the drift and other parameters. The phase diagram is similar to that obtained by Nelson and coworkers from a deterministic, spatially continuous model of a bacterial population undergoing convection in a heterogeneous medium.Comment: 8 papes, 12 figure

Epidemic threshold in structured scale-free networks

We analyze the spreading of viruses in scale-free networks with high clustering and degree correlations, as found in the Internet graph. For the Suscetible-Infected-Susceptible model of epidemics the prevalence undergoes a phase transition at a finite threshold of the transmission probability. Comparing with the absence of a finite threshold in networks with purely random wiring, our result suggests that high clustering and degree correlations protect scale-free networks against the spreading of viruses. We introduce and verify a quantitative description of the epidemic threshold based on the connectivity of the neighborhoods of the hubs.Comment: 4 pages, 4 figure

Conversion to sirolimus for chronic renal allograft dysfunction: risk factors for graft loss and severe side effects

We retrospectively reviewed our experience with 45 kidney transplant recipients (KTR) that were switched from CNI to SRL, mainly for chronic allograft dysfunction (CAD) (41/45). The mean serum creatinine at switch was 2.5 ± 0.8 mg/dl. At 1 year, patient survival was 93%. Death-censored graft survival was 67% at 1 year and 54% at 2 years. SRL was stopped because of severe side effects in 15 patients. Among these, eight patients developed ‘de novo’ high-grade proteinuria. Univariate analysis revealed that (1) a higher SRL level at 1 month was a predictor of SRL withdrawal due to severe side effects (P = 0.006), and (2) predictors of graft failure after SRL conversion were low SRL loading dose (P = 0.03) and a higher creatinine level at conversion (P = 0.003)