On estimating the basic reproduction number in distinct stages of a contagious disease spreading

In epidemiology, the basic reproduction number R-0 is usually defined as the average number of new infections caused by a single infective individual introduced into a completely susceptible population. According to this definition. R-0 is related to the initial stage of the spreading of a contagious disease. However, from epidemiological models based on ordinary differential equations (ODE), R-0 is commonly derived from a linear stability analysis and interpreted as a bifurcation parameter: typically, when R-0 >1, the contagious disease tends to persist in the population because the endemic stationary solution is asymptotically stable: when R-0 <1, the corresponding pathogen tends to naturally disappear because the disease-free stationary solution is asymptotically stable. Here we intend to answer the following question: Do these two different approaches for calculating R-0 give the same numerical values? In other words, is the number of secondary infections caused by a unique sick individual equal to the threshold obtained from stability analysis of steady states of ODE? For finding the answer, we use a susceptibleinfective-recovered (SIR) model described in terms of ODE and also in terms of a probabilistic cellular automaton (PCA), where each individual (corresponding to a cell of the PCA lattice) is connected to others by a random network favoring local contacts. The values of R-0 obtained from both approaches are compared, showing good agreement. (C) 2012 Elsevier B.V. All rights reserved.

Optimal Code Set Selection and Security Issues in Spectral Phase-Encoded Time Spreading (SPECTS) OCDMA Systems

In this paper, we perform a thorough analysis of a spectral phase-encoded time spreading optical code division multiple access (SPECTS-OCDMA) system based on Walsh-Hadamard (W-H) codes aiming not only at finding optimal code-set selections but also at assessing its loss of security due to crosstalk. We prove that an inadequate choice of codes can make the crosstalk between active users to become large enough so as to cause the data from the user of interest to be detected by other user. The proposed algorithm for code optimization targets code sets that produce minimum bit error rate (BER) among all codes for a specific number of simultaneous users. This methodology allows us to find optimal code sets for any OCDMA system, regardless the code family used and the number of active users. This procedure is crucial for circumventing the unexpected lack of security due to crosstalk. We also show that a SPECTS-OCDMA system based on W-H 32(64) fundamentally limits the number of simultaneous users to 4(8) with no security violation due to crosstalk. More importantly, we prove that only a small fraction of the available code sets is actually immune to crosstalk with acceptable BER (<10(-9)) i.e., approximately 0.5% for W-H 32 with four simultaneous users, and about 1 x 10(-4)% for W-H 64 with eight simultaneous users.

Speckle patterns during the spreading of lung surfactant.

Pulmonary surfactant is a very important product in the medical treatment of the syndrome of insufficiency respiratory in neonates. The synthesis of this surfactant in labs need to optimize the rate of spreading in the alveolar interstitial liquid obtaining a monolayer of the phospholipids membrane base capable to maintains several of the dynamical properties of the respiratory system during breathing. The recover of theses mechanical properties has to be archived using the minimal quantities of product and with the optimal proteins composition (SP-B in special). In this paper we show our results of obtaining and process speckle pattern images of the spreading of phospholipids membrane composed the matrix of this product (DPPC) when physiologic interstitial liquid are presented.

The effects of river discharge and seasonal winds on the shelf off southeastern South America

The Rio de la Plata waters form a low salinity tongue that affects the circulation, stratification and the distributions of nutrients and biological species over a wide extent of the adjacent continental shelf. The plume of coastal waters presents a seasonal meridional displacement reaching lower latitudes (28,S) during austral winter and 32 degrees S during summer. Historical data suggests that the wind causes the alongshore shift, with southwesterly (SW) winds forcing the plume to lower latitudes in winter while summer dominant northeasterly (NE) winds force its southward retreat. To establish the connection between wind and outflow variations on the distribution of the coastal waters, we conducted two quasi-synoptic surveys in the region of Plata influence on the continental shelf and slope of southeastern South America, between Mar del Plata, Argentina and the northern coast of Santa Catarina, Brazil. We observed that: (A) SW winds dominating in winter force the northward spreading of the plume to low latitudes even during low river discharge periods; (B) NE winds displace the plume southward and spread the low salinity waters offshore over the entire width of the continental shelf east of the Plata estuary. The southward retreat of the plume in summer leads to a volume decrease of low salinity waters over the shelf. This volume is compensated by an increase of Tropical waters, which dominate the northern shelf. The subsurface transition between Subantarctic and Subtropical Shelf Waters, the Subtropical Shelf Front, and the subsurface water mass distribution, however, present minor seasonal variations. Along shore winds also influence the dynamics and water mass variations along the continental shelf area. In areas under the influence of river discharge, Subtropical Shelf Waters are kept away from the coastal region. When low salinity waters retreat southward, NE winds induce a coastal upwelling system near Santa Marta Cape. In summer, solar radiation promotes the establishment of a strong thermocline that increases buoyancy and further enhances the offshore displacement of low salinity waters under the action of NE winds. (C) 2008 Elsevier Ltd. All rights reserved.

Predicting epidemic outbreak from individual features of the spreaders

Knowing which individuals can be more efficient in spreading a pathogen throughout a determinate environment is a fundamental question in disease control. Indeed, over recent years the spread of epidemic diseases and its relationship with the topology of the involved system have been a recurrent topic in complex network theory, taking into account both network models and real-world data. In this paper we explore possible correlations between the heterogeneous spread of an epidemic disease governed by the susceptible-infected-recovered (SIR) model, and several attributes of the originating vertices, considering Erdos-Renyi (ER), Barabasi-Albert (BA) and random geometric graphs (RGG), as well as a real case study, the US air transportation network, which comprises the 500 busiest airports in the US along with inter-connections. Initially, the heterogeneity of the spreading is achieved by considering the RGG networks, in which we analytically derive an expression for the distribution of the spreading rates among the established contacts, by assuming that such rates decay exponentially with the distance that separates the individuals. Such a distribution is also considered for the ER and BA models, where we observe topological effects on the correlations. In the case of the airport network, the spreading rates are empirically defined, assumed to be directly proportional to the seat availability. Among both the theoretical and real networks considered, we observe a high correlation between the total epidemic prevalence and the degree, as well as the strength and the accessibility of the epidemic sources. For attributes such as the betweenness centrality and the k-shell index, however, the correlation depends on the topology considered.

Particle Competition and Cooperation in Networks for Semi-Supervised Learning

Semi-supervised learning is one of the important topics in machine learning, concerning with pattern classification where only a small subset of data is labeled. In this paper, a new network-based (or graph-based) semi-supervised classification model is proposed. It employs a combined random-greedy walk of particles, with competition and cooperation mechanisms, to propagate class labels to the whole network. Due to the competition mechanism, the proposed model has a local label spreading fashion, i.e., each particle only visits a portion of nodes potentially belonging to it, while it is not allowed to visit those nodes definitely occupied by particles of other classes. In this way, a "divide-and-conquer" effect is naturally embedded in the model. As a result, the proposed model can achieve a good classification rate while exhibiting low computational complexity order in comparison to other network-based semi-supervised algorithms. Computer simulations carried out for synthetic and real-world data sets provide a numeric quantification of the performance of the method.

Phylogeography of Rift Valley Fever Virus in Africa Reveals Multiple Introductions in Senegal and Mauritania

Rift Valley Fever (RVF) virus (Family Bunyaviridae) is an arthropod-borne RNA virus that infects primarily domestic ruminants and occasionally humans. RVF epizootics are characterized by numerous abortions and mortality among young animals. In humans, the illness is usually characterized by a mild self-limited febrile illness, which could progress to more serious complications. RVF virus is widespread and endemic in many regions of Africa. In Western Africa, several outbreaks have been reported since 1987 when the first major one occurred at the frontier of Senegal and Mauritania. Aiming to evaluate the spreading and molecular epidemiology in these countries, RVFV isolates from 1944 to 2008 obtained from 18 localities in Senegal and Mauritania and 15 other countries were investigated. Our results suggest that a more intense viral activity possibly took place during the last century compared to the recent past and that at least 5 introductions of RVFV took place in Senegal and Mauritania from distant African regions. Moreover, Barkedji in Senegal was possibly a hub associated with the three distinct entries of RVFV in West Africa.

Spiroplasma in Drosophila melanogaster Populations: Prevalence, Male-Killing, Molecular Identification, and No Association with Wolbachia

Spiroplasma endosymbionts are maternally transmitted bacteria that may kill infected sons resulting in the production of female-biased broods. The prevalence of male killers varies considerably both between and within species. Here, we evaluate the spatial and temporal status of male-killing and non-male-killing Spiroplasma infection in three Brazilian populations of Drosophila melanogaster, nearly a decade after the first occurrence report for this species. The incidence of the male-killing Spiroplasma ranged from close to 0 to 17.7 % (so far the highest estimate for a Drosophila species) with a suggestion of temporal decline in a population. We also found non-male-killing Spiroplasma coexisting in one population at lower prevalence (3-5 %), and we did not detect it in the other two. This may be taken as a suggestion of a spreading advantage conferred by the male-killing strategy. Sequencing two loci, we identified the phylogenetic position of Spiroplasma strains from the three localities, showing that all strains group closely in the poulsonii clade. Due to intensive sampling effort, we were able to test the association between Spiroplasma infections and another widespread endosymbiont, Wolbachia, whose prevalence ranged from 81.8 to 100 %. The prevalence of Wolbachia did not differ between Spiroplasma-infected and uninfected strains in our largest sample nor were the prevalences of the two endosymbionts associated across localities.

Neurogenic neuroprotection: Future perspectives

Neurogenic neuroprotection elicited by deep brain stimulation is emerging as a promising approach for treating patients with ischemic brain lesions. In rats, stimulation of the fastigial nucleus, but not dentate nucleus, has been shown to reduce the volume of focal infarction. Protection of neural tissue is a rapid intervention that has a relatively long-lasting effect, rendering fastigial nucleus stimulation (FNS) a potentially valuable method for clinical application. We review some of the main findings of animal experimental research from a clinical perspective. Results: Although the complete mechanisms of neuroprotection induced by FNS remain unclear, important data has been presented in the last two decades. The acute effect of electrical stimulation of the fastigial nucleus is likely mediated by a prolonged opening of potassium channels, and the sustained effect appears to be linked to inhibition of the apoptotic cascade. A better understanding of the cellular and molecular mechanisms underlying neurogenic neuroprotection by stimulation of deep brain nuclei, with special attention to the fastigial nucleus, can contribute toward improving neurological outcomes in ischemic brain insults.

Late entry into HIV care: lessons from Brazil, 2003 to 2006

Background: To ascertain the population rates and proportion of late entry into HIV care, as well as to determine whether such late entry correlates with individual and contextual factors. Methods: Data for the 2003-2006 period in Brazil were obtained from public health records. A case of late entry into HIV care was defined as one in which HIV infection was diagnosed at death, one in which HIV infection was diagnosed after the condition of the patient had already been aggravated by AIDS-related diseases, or one in which the CD4(+) T-cell count was <= 200 cells/mm(3) at the time of diagnosis. We also considered extended and stricter sets of criteria (in which the final criterion was <= 350 cells/mm(3) and <= 100 cells/mm(3), respectively). The estimated risk ratio was used in assessing the effects of correlates, and the population rates (per 100,000 population) were calculated on an annual basis. Results: Records of 115,369 HIV-infected adults were retrieved, and 43.6% (50,358) met the standard criteria for late entry into care. Diagnosis at death accounted for 29% (14,457) of these cases. Late entry into HIV care (standard criterion) was associated with certain individual factors (sex, age, and transmission category) and contextual factors (region with less economic development/increasing incidence of AIDS, lower local HIV testing rate, and smaller municipal population). Use of the extended criteria increased the proportion of late entry by 34% but did not substantially alter the correlations analyzed. The overall population rate of late entry was 9.9/100,000 population, specific rates being highest for individuals in the 30-59 year age bracket, for men, and for individuals living in regions with greater economic development/higher HIV testing rates, collectively accounting for more than half of the cases observed. Conclusions: Although the high proportion of late entry might contribute to spreading the AIDS epidemic in less developed regions, most cases occurred in large cities, with broader availability of HIV testing, and in economically developed regions.

Toll-like receptor 9 activation in neutrophils impairs chemotaxis and reduces sepsis outcome

Objectives: To investigate the role of toll-like receptor 9 on sepsis-induced failure of neutrophil recruitment to the site of infection. Design: Prospective experimental study. Setting: University research laboratory. Interventions: Model of polymicrobial sepsis induced by cecal ligation and puncture in wild-type and toll-like receptor 9-deficient mice. Measurements and Main Results: Toll-like receptor 9-deficient mice with cecal ligation and puncture-induced severe sepsis did not demonstrate failure of neutrophil migration and consequently had a low systemic inflammatory response and a high survival rate. Upon investigating the mechanism by which toll-like receptor 9-deficiency prevents the failure of neutrophil migration, it was found that neutrophils derived from toll-like receptor 9-deficient mice with cecal ligation and puncture induced severe sepsis expressed high levels of chemokine C-X-C motif receptor 2 (CXCR2) and had reduced induction of G-protein-coupled receptor kinase 2. Conclusions: These findings suggest that the poor outcome of severe sepsis is associated with toll-like receptor 9 activation in neutrophils, which triggers G-protein-coupled receptor kinase 2 expression and CXCR2 downregulation. These events account for the reduction of neutrophil migration to the site of infection, with consequent spreading of the infection, onset of the systemic inflammatory response, and a decrease in survival. (Crit Care Med 2012; 40:2631-2637)

Transplant-Associated and Blood Transfusion-Associated Tropical and Parasitic Infections

Blood transfusion and transplantation may represent efficient mechanisms of spreading infectious agents to naive populations. In the developed countries, as a consequence of globalization, several factors such as international commerce, tourism, and immigration have acted as important features for the emergence or reemergence of infectious diseases previously referred to as tropical. This article reviews the relevant bacterial, protozoan and viral infections that are more frequently associated with blood transfusion and/or solid organ or marrow transplantation and may affect susceptible populations worldwide.

Controlling chaos in wave-particle interactions

We analyze the behavior of a relativistic particle moving under the influence of a uniform magnetic field and a stationary electrostatic wave. We work with a set of pulsed waves that allows us to obtain an exact map for the system. We also use a method of control for near-integrable Hamiltonians that consists of the addition of a small and simple control term to the system. This control term creates invariant tori in phase space that prevent chaos from spreading to large regions, making the controlled dynamics more regular. We show numerically that the control term just slightly modifies the system but is able to drastically reduce chaos with a low additional cost of energy. Moreover, we discuss how the control of chaos and the consequent recovery of regular trajectories in phase space are useful to improve regular particle acceleration.

Interannual variation in commercial oyster (Crassostrea gigas) farming in the sea (Florianopolis, Brazil, 27 degrees 44 ' S; 48 degrees 33 ' W) in relation to temperature, chlorophyll a and associated oceanographic conditions

Aquaculture of filter-feeding bivalve mollusks involves the fruitful conversion of marine particulate organic matter into premium protein of high nutritive value. Culture performance of bivalves is largely dependent on hydrological conditions and directly affected by e. g. temperature and chlorophyll levels. Accordingly, these parameters may be related with seasonality but also with oceanographic features combined with climate events. Yields of Pacific cupped oyster (Crassostrea gigas) reared at commercial procedures in suspended structures (long-lines) in a sheltered bay in Southern Brazil (Santa Catarina State, 27S 43'; 48 W 30') were evaluated in relation to local environmental conditions: sea surface temperature, chlorophyll a concentration, and associate effects of cold fronts events and El Nino and La Nina periods. Outputs from four consecutive commercial crop years were analyzed (2005/06, 2006/07, 2007/08, 2008/09) in terms of oyster survival and development time during the following grow-out phases of the culture cycle: seed to juvenile, juvenile to adult, adult to marketable. Since culture management and genetics were standardized significant differences verified among crop performance could be mostly related to environmental effects. Time series of temperature and chlorophyll a (remote sensing data) from crop periods displayed significant seasonal and interannual variation. As expected, performance during initial grow-out stages (seed to juvenile) was critical for final crop yield. Temperature was the main factor affecting survival in these initial stages with a trend of negative correlation, though not statistically significant. On the other hand, oyster development rate was significantly and positively affected by chlorophyll a concentration. Chlorophyll a values could be increased by upwelled cold nutrient-rich South Atlantic Central Water (SACW, related to predominant Northern winds) though further dependent on occurrence of Southern winds (cold fronts) to assist seawater penetration into the sheltered farming area. Lower salinity nutrient-rich northward drifted waters from La Plata River discharge may also result in chlorophyll a rise in the farming area. The El Nino period (July 2006 to February 2007) coincided with lower chlorophyll a levels in the farming site that may be related to both decreased number of cold fronts as well as predominance of Northern winds that retain northward spreading of La Plata River discharge waters. In contrast, the La Nina period (August 2007 to June 2008) corresponded to higher chlorophyll a values in the farming area by both upwelling of SACW and penetration of La Plata River discharge water assisted by increased occurrence of Southern winds and cold fronts. The recognition of the potentially changing climate and effects upon the environment will be an important step in planning future development of bivalve aquaculture.

Crotoxin, a rattlesnake toxin, induces a long-lasting inhibitory effect on phagocytosis by neutrophils

Crotalus durissus terrificus snake venom (CdtV) has long-lasting anti-inflammatory properties and inhibits the spreading and phagocytic activity of macrophages. Crotoxin (CTX), the main component of CdtV, is responsible for these effects. Considering the role of neutrophils in the inflammatory response and the lack of information about the effect of CdtV on neutrophils, the aim of this study was to investigate the effect of CdtV and CTX on two functions of neutrophils, namely phagocytosis and production of reactive oxygen species, and on the intracellular signaling involved in phagocytosis, particularly on tyrosine phosphorylation and rearrangements of the actin cytoskeleton. Our results showed that the incubation of neutrophils with CdtV or CTX, at different concentrations, or the subcutaneous injection of CdtV or CTX in rats two hours or one, four or 14 days before or one hour after the induction of inflammation inhibited the phagocytic activity of neutrophils. Furthermore, these in vitro and in vivo effects were associated with CdtV and CTX inhibition of tyrosine phosphorylation and consequently actin polymerization. Despite the inhibitory effect on phagocytosis, this study demonstrated that CdtV and CTX did not alter the production of the main reactive oxygen species. Therefore, this study characterized, for the first time, the actions of CdtV on neutrophils and demonstrated that CTX induces a long-lasting inhibition of tyrosine phosphorylation and consequently phagocytosis. We suggest that CTX represents a potential natural product in controlling inflammatory diseases, since a single dose exerts a long-lasting effect on intracellular signaling involved in phagocytosis by neutrophils.