A mathematical model of the dynamics of the immune system is considered to illustrate the effect of its response to HIV infection, i.e. on viral growth and on T-cell dynamics. The specific immune response is measured by the levels of cytotoxic lymphocytes in a human body. The existence and stability analyses are performed for infected steady state and uninfected steady state. In order to keep infection under control, roles of drug therapies are analyzed in the presence (...) of efficient immune response. Numerical simulations are computed and exhibited to illustrate the support of the immune system to drug therapies, so as to ensure the decay of infection and to maintain the level of healthy cells. (shrink)

In order to understand the transmission of a disease across a population we will have to understand not only the dynamics of contact infection but the transfer of health-care beliefs and resulting health-care behaviors across that population. This paper is a first step in that direction, focusing on the contrasting role of linkage or isolation between sub-networks in (a) contact infection and (b) belief transfer. Using both analytical tools and agent-based simulations we show that it is the (...) structure of a network that is primary for predicting contact infection—whether the networks or sub-networks at issue are distributed ring networks or total networks (hubs, wheels, small world, random, or scale-free for example). Measured in terms of time to total infection, degree of linkage between sub-networks plays a minor role. The case of belief is importantly different. Using a simplified model of belief reinforcement, and measuring belief transfer in terms of time to community consensus, we show that degree of linkage between sub-networks plays a major role in social communication of beliefs. Here, in contrast to the case of contract infection, network type turns out to be of relatively minor importance. What you believe travels differently. In a final section we show that the pattern of belief transfer exhibits a classic power law regardless of the type of network involved. (shrink)

In this paper, we propose two HIV infection models with specific nonlinear incidence rate by including a class of infected cells in the eclipse phase. The first model is described by ordinary differential equations and generalizes a set of previously existing models and their results. The second model extends our ODE model by taking into account the diffusion of virus. Furthermore, the global stability of both models is investigated by constructing suitable Lyapunov functionals. Finally, we check our theoretical results (...) with numerical simulations. (shrink)

In this paper we make a simple theoretical point using a practical issue as an example. The simple theoretical point is that robustness is not 'all or nothing': in asking whether a system is robust one has to ask 'robust with respect to what property?' and 'robust over what set of changes in the system?' The practical issue used to illustrate the point is an examination of degrees of linkage between sub-networks and a pointed contrast in robustness and fragility between (...) the dynamics of (1) contact infection and (2) information transfer or belief change. Time to infection across linked sub-networks, it turns out, is fairly robust with regard to the degree of linkage between them. Time to infection is fragile and sensitive, however, with regard to the type of sub-network involved: total, ring, small world, random, or scale-free. Aspects of robustness and fragility are reversed where it is belief updating with reinforcement rather than infection that is at issue. In information dynamics, the pattern of time to consensus is robust across changes in network type but remarkably fragile with respect to degree of linkage between sub-networks. These results have important implications for public health interventions in realistic social networks, particularly with an eye to ethnic and socio-economic sub-communities, and in social networks with sub-communities changing in structure or linkage. (shrink)

We analyze the dynamics of nosocomial infections in intensive care units (ICUs) by using a Markov chain model. Since population size in the ICU is small, in contrast to previous studies, we concentrate on the analytical solution rather than using simulation. We investigate how changes in the system parameters affect to some important behavioral indicators of the spread of the pathogen. We also present an exact measure of the number of secondary cases of infection produced by one colonized (...) patient. (shrink)

Whooping cough is a highly transmitted disease around the world. According to the World Health Organization, 0.15 million cases had reported globally in 2018. Most of the Asian and African states are infected regions. Through the study, we investigated the whole population into the four classes susceptible, exposed, infected, and vaccinated or recovered. The transmission dynamics of whooping cough disease are studied analytically and numerically. Analytical analyses are positivity, boundedness, reproduction number, equilibria, and local and global stabilities. In numerical (...) analysis, we developed an implicit numerical integration scheme consistent with the biological problem’s properties. The analysis of the implicit method for the said model is dynamically consistent, positive, and bounded. Furthermore, an implicit numerical integration scheme is suitable for studying a particular epidemic model such as the whooping cough disease. (shrink)

A new multi-stage deterministic model for the transmission dynamics of syphilis, which incorporates disease transmission by individuals in the early latent stage of syphilis infection and the reversions of early latent syphilis to the primary and secondary stages, is formulated and rigorously analysed. The model is used to assess the population-level impact of preventive and therapeutic measures against the spread of the disease in a community. It is shown that the disease-free equilibrium of the model is globally-asymptotically stable (...) whenever the associated control reproduction number is less than unity. A special case of the model is shown to have a unique and globally-asymptotically stable endemic equilibrium whenever the associated reproduction number exceeds unity. Uncertainty and sensitivity analysis of the model, using parameter values and ranges relevant to syphilis transmission dynamics in Nigeria, show that the top three parameters that drive the syphilis infection are the disease transmission rate, compliance in condom use and efficacy of condom. Numerical simulations of the model show that the targeted treatment of secondary syphilis cases is more effective than the targeted treatment of individuals in the primary or early latent stage of syphilis infection. (shrink)

Beyond belief change and meme adoption, both genetics and infection have been spoken of in terms of information transfer. What we examine here, concentrating on the specific case of transfer between sub-networks, are the differences in network dynamics in these cases: the different network dynamics of germs, genes, and memes. Germs and memes, it turns out, exhibit a very different dynamics across networks. For infection, measured in terms of time to total infection, it is (...) network type rather than degree of linkage between sub-networks that is of primary importance. For belief transfer, measured in terms of time to consensus, it is degree of linkage rather than network type that is crucial. Genes model each of these other dynamics in part, but match neither in full. For genetics, like belief transfer and unlike infection, network type makes little difference. Like infection and unlike belief, on the other hand, the dynamics of genetic information transfer within single and between linked networks are much the same. In ways both surprising and intriguing, transfer of genetic information seems to be robust across network differences crucial for the other two. (shrink)

It is widely accepted that the way information transfers across networks depends importantly on the structure of the network. Here, we show that the mechanism of information transfer is crucial: in many respects the effect of the specific transfer mechanism swamps network effects. Results are demonstrated in terms of three different types of transfer mechanism: germs, genes, and memes. With an emphasis on the specific case of transfer between sub-networks, we explore both the dynamics of each of these across (...) networks and a measure of their comparative fitness. Germ and meme transfer exhibit very different dynamics across linked networks. For germs, measured in terms of time to total infection, network type rather than degree of linkage between sub-networks is the primary factor. For memes or belief transfer, measured in terms of time to consensus, it is the opposite: degree of linkage trumps network type in importance. The dynamics of genetic information transfer is unlike either germs or memes. Transfer of genetic information is robust across network differences to which both germs and memes prove sensitive. We also consider function: how well germ, gene, and meme transfer mechanisms can meet their respective objectives of infecting the population, mixing and transferring genetic information, and spreading a message. A shared formal measure of fitness is introduced for purposes of comparison, again with an emphasis on linked sub-networks. Meme transfer proves superior to transfer by genetic reproduction on that measure, with both memes and genes superior to infection dynamics across all networks types. What kinds of network structure optimize fitness also differ among the three. Both germs and genes show fairly stable fitness with added links between sub-networks, but genes show greater sensitivity to the structure of sub-networks at issue. Belief transfer, in contrast to the other two, shows a clear decline in fitness with increasingly connected networks. When it comes to understanding how information moves on networks, our results indicate that questions of information dynamics on networks cannot be answered in terms of networks alone. A primary role is played by the specific mechanism of information transfer at issue. We must first ask about how a particular type of information moves. (shrink)

We take a logical approach to threshold models, used to study the diffusion of opinions, new technologies, infections, or behaviors in social networks. Threshold models consist of a network graph of agents connected by a social relationship and a threshold value which regulates the diffusion process. Agents adopt a new behavior/product/opinion when the proportion of their neighbors who have already adopted it meets the threshold. Under this diffusion policy, threshold models develop dynamically towards a guaranteed fixed point. We construct a (...) minimal dynamic propositional logic to describe the threshold dynamics and show that the logic is sound and complete. We then extend this framework with an epistemic dimension and investigate how information about more distant neighbors’ behavior allows agents to anticipate changes in behavior of their closer neighbors. Overall, our logical formalism captures the interplay between the epistemic and social dimensions in social networks. (shrink)

The SARS‐CoV‐2 virus is responsible for the COVID‐19 pandemic the world experience since 2019. The protein responsible for the first steps of cell invasion, the spike protein, has probably received the most attention in light of its central role during infection. Computational approaches are among the tools employed by the scientific community in the enormous effort to study this new affliction. One of these methods, namely molecular dynamics (MD), has been used to characterize the function of the spike (...) protein at the atomic level and unveil its structural features from a dynamic perspective. In this review, we focus on these main findings, including spike protein flexibility, rare S protein conformational changes, cryptic epitopes, the role of glycans, drug repurposing, and the effect of spike protein variants. (shrink)

We study the SIS and SIRI epidemic models discussing different approaches to compute the thresholds that determine the appearance of an epidemic disease. The stochastic SIS model is a well known mathematical model, studied in several contexts. Here, we present recursively derivations of the dynamic equations for all the moments and we derive the stationary states of the state variables using the moment closure method. We observe that the steady states give a good approximation of the quasi-stationary states of the (...) SIS model. We present the relation between the SIS stochastic model and the contact process introducing creation and annihilation operators. For the spatial stochastic epidemic reinfection model SIRI, where susceptibles S can become infected I, then recover and remain only partial immune against reinfection R, we present the phase transition lines using the mean field and the pair approximation for the moments. We use a scaling argument that allow us to determine analytically an explicit formula for the phase transition lines in pair approximation. (shrink)

The molecular biology of viruses can be effectively described by kinetic logic as several feedback loops are implicated in all viral cycles and as viral proteins generally display several functions. We applied this method to the study of the rhabdovirus cycle.Formally, the dynamics of the model are explored on the basis of a discrete caricature (kinetic logic), with special emphasis on the role of the constitutive feedback loops to determine the essential dynamical behaviour of the viral cycle. From a (...) biological point of view, our model accounts for several stable regimes or attractors: healthy cells, acute infection and different kinds of persistent infections, a multistationarity in good agreement with the existence of several positive feedback loops in our system. (shrink)

In the real world, individual resources are crucial for patients when epidemics outbreak. Thus, the coupled dynamics of resource diffusion and epidemic spreading have been widely investigated when the recovery of diseases significantly depends on the resources from neighbors in static social networks. However, the social relationships of individuals are time-varying, which affects such coupled dynamics. For that, we propose a coupled resource-epidemic dynamic model on a time-varying multiplex network to synchronously simulate the resource diffusion and epidemic spreading (...) in dynamic social networks. The equilibrium analysis of the coupled model is conducted in a general scenario where the resource generation varies between susceptible and infected states and the recovery rate changes between resourceful and noresource states. By using the microscopic Markov chain approach and Monte Carlo simulations, we determine a probabilistic framework of the intralayer and interlayer dynamic processes of the coupled model and obtain the outbreak threshold of epidemic spreading. Meanwhile, the experimental results show the trivially asymmetric interactions between resource diffusion and epidemic spreading. They also indicate that the stronger activity heterogeneity and the larger contact capacity of individuals in the resource layer can more greatly promote resource diffusion, effectively suppressing epidemic spreading. However, these two individual characters in the epidemic layer can cause more resource depletion, which greatly promotes epidemic spreading. Furthermore, we also find that the contact capacity finitely impacts the coupled dynamics of resource diffusion and epidemic spreading. (shrink)

This paper describes a traditional SIR type epidemic model with saturated infection rate and treatment function. The dynamics of the model is studied from the point of view of stability and bifurcation. Basic reproduction number is obtained and it is shown that the model system may possess a backward bifurcation. The global asymptotic stability of the endemic equilibrium is studied with the help of a geometric approach. Optimal control problem is formulated and solved. Some numerical simulation works are (...) carried out to validate our analytical results. (shrink)

It has been demonstrated that the propagation of information and awareness regarding a disease can assist in containing the outbreak of epidemics. Previous models for this coevolving usually introduced the dependence between these two processes by setting a lower but time-independent infection rate for individuals with awareness. However, a realistic scenario can be more complicated, as individual vigilance and the adopted protective measures may depend on the extent of the discussion on the disease, whereas individuals may be irrational or (...) lack relevant knowledge, leading to improper measures being taken. These can introduce a time-varying dependence between epidemic dynamics and awareness prevalence and may weaken the effect of spreading awareness in containing a pandemic. To better understand this effect, we introduce a nonlinear dependence of the epidemic infection rate on awareness prevalence, focusing on the effect of different forms of dependence on the coevolving dynamics. We demonstrate that a positive correlation between vigilance and awareness prevalence can enhance the effect of information spreading in suppressing epidemics. However, this enhancement can be weakened if some individuals are irrational. Our results demonstrate the importance of rational behavior in the strategy of containing epidemics by propagation of disease information. (shrink)

According to Kant, justifying the application of mathematics to objects in natural science requires metaphysically constructing the concept of matter. Kant develops these constructions in the Metaphysical Foundations of Natural Science (MAdN). Kant’s specific aim is to develop a dynamic theory of matter to replace corpuscular theory. In his Preface Kant claims completely to exhaust the metaphysical doctrine of body, but in the General Remark to MAdN ch. 2, “Dynamics,” Kant admits that once matter is reconceived as basic forces, (...) it is no longer possible to construct the concept of matter. I argue that Kant’s admission is only the tip of the problem, and that none of Kant’s commentators has fully grasped the problems infecting the MAdN that underlie Kant’s admission. I show that Kant’s proof that matter consists of forces is fallacious. I then re-analyze the circularity in Kant’s definition of density, criticizing both Adickes’ formulations and his later dissolution of it. I also show that a third circularity infects the relations between Kant’s treatment of “Dynamics” and “Mechanics” (MAdN ch. 3). These three fundamental problems demonstrate the untenability of Kant’s metaphysical method, and they require the radical revision of the relation between mathematics and metaphysics Kant undertakes in his opus postumum. I show that some of Kant’s most surprising and critical later claims about the Critical philosophy are correct, and that they require the sorts of remedies Kant contemplates in the opus postumum. (I defend the essentially correct analyses offered by Burkhard Tuschling and Eckart Forster against criticisms by Michael Friedman.). (shrink)

This paper is devoted to develop a nonlocal and time-delayed reaction-diffusion model for HIV infection within host cell-to-cell viral transmissions. In a bounded spatial domain, we study threshold dynamics in terms of basic reproduction numberR0for the heterogeneous model. Our results show that ifR0 1, virus will persist in the host environment.

In this study, for COVID-19, we divide people into four categories: susceptible S t, closely contacted C t, infective I t, and removed R t according to the current epidemic situation and then investigate two models: the SCIR models with immigration and without immigration. For the former, Model 1, we obtain the condition for global stability of its disease-free equilibrium. For the latter, Model 2, we establish the local asymptotic stability of its endemic equilibrium by constructing Lyapunov function. Afterwards, by (...) the bifurcation theory, we qualitatively analyze the properties of its Hopf bifurcations of the latter. Finally, numerical simulations are given to illustrate the obtained results of two models. The results imply the importance of finding closely contacted and overseas imports on epidemic control. It indicates that not only the incubation delay τ is crucial for the containment of the COVID-19 but also the scientific and rigorous containment measures are the key factors of the success of the containment. (shrink)

Atmospheric pollution is deteriorating, which has affected the evolution of respiratory disease for the exposed human worldwide. Thus, exploring the influence of air pollution on the evolution of disease transmission dynamics is a significant issue. In this article, a stochastic susceptible-infective epidemic model in a polluted atmospheric environment is investigated. The existence and uniqueness of the global positive solution are established. In virtue of the aggregation methods and Lyapunov function, the sufficient conditions of disease extinction, persistence, and existence of (...) the stationary distribution are established, respectively. TakingPM2.5concentration as the air pollutant index, numerical simulations are carried out to support these results. Our results indicated that the disease transmission dynamics are significantly associated with the environmental atmospheric pollution and fluctuation. (shrink)

Modelling of contagious disease usually employs compartmental SEIR-like models where the waiting times in respective compartments are exponentially distributed. In this paper, we are interested in investigating how the distributions of sojourn times in infective compartments affect the dynamics and persistence of the contagious bovine pleuropneumonia, a chronic respiratory disease of cattle. Two kinds of extreme distributions of the sojourn times are considered: a Dirac delta-function and truncated Gaussian function leading to a model with (non-constant) delay and the classical (...) exponential distribution that stands for a model without delay. Expressions of the basic reproductive numbers are derived and dynamical behaviours are discussed for the three models. It is found that the spreading of disease exhibits wave-like oscillations for the time-delay dynamics. In contrast, the disease appears to last longer when the spreading is described by the classical dynamics without delay. Subsequently, the time-delay dynamics turns out to be more appropriate for the description of an experimental epidemic of CBPP. (shrink)

This paper reassesses Robert Koch’s work on tropical infections of humans and cattle as being inspired by an underlying interest in epidemiology. Such an interest was developed from the early 1890s when it became clear that an exclusive focus on pathogens was insufficient as an approach to explain the genesis and dynamics of epidemics. Koch, who had failed to do so before, now highlighted differences between infection and disease and described the role of various sub-clinical states of disease (...) in the propagation and—consequently—in the control of epidemics. Studying pathologies of men and cattle in tropical countries eventually facilitated the application of such measures in Europe through the screening of healthy carriers of typhoid, which was carried out in 1902. The concept of the carrier state can be understood as a spin-off from tropical medicine into the study and control of infectious disease in Europe. With it travelled assumptions that were typical for colonial and veterinary medicine where the health of indigenous individuals or cattle would be a secondary objective compared to the control of diseases in populations. (shrink)

Neospora caninum infection, one of the major causes of abortions in dairy cattle, has brought a huge loss to farmers worldwide. In this study, we develop a six-compartment susceptible-infected model of N. caninum transmission which is later reduced to a two-equation system. Potential controls including medication, test-and-cull, and vaccination are proposed and analyzed, and the corresponding reproduction numbers are derived. The conditions for the global stabilities of disease-free and endemic equilibria are investigated with analytical solutions and geometric approach. Furthermore, (...) uncertainty and sensitivity analysis shows that three control strategies are effective towards the varied environment, whereas the effectiveness of each measure highly depends on parameters related to control actions. Dynamics of reproduction numbers illustrate that disease elimination can be achieved by three types of controls: adopting medication with medicine efficacy higher than 0.4 to prevent vertical transmission, implementing test-and-cull with culling coverage larger than 0.3, and taking vaccine with coverage larger than 0.1. Numerical results suggest that preventive measures should at least include the prevention of access of other hosts, such as dogs, to cattle; otherwise, these control measures will lose effectiveness. Our presented study provides guidance for decision-making on N. caninum infected farm management. (shrink)

Virus and information spreading dynamics widely exist in complex systems. However, systematic study still lacks for the interacting spreading dynamics between the two types of dynamics. This paper proposes a mathematical model on multiplex networks, which considers the heterogeneous susceptibility and infectivity in two subnetworks. By using a heterogeneous mean-field theory, we studied the dynamic process and outbreak threshold of the system. Through extensive numerical simulations on artificial networks, we find that the virus’s spreading dynamics can (...) be suppressed by increasing the information spreading probability, decreasing the protection power, or decreasing the susceptibility and infectivity. (shrink)

In this paper, a nonlinear dynamical system is proposed and qualitatively analyzed to study the dynamics and effects of HIV-malaria co-infection in the workplace. Basic reproduction numbers of sub-models are derived and are shown to have LAS disease-free equilibria when their respective basic reproduction numbers are less than unity. Conditions for existence of endemic equilibria of sub-models are also derived. Unlike the HIV-only model, the malaria-only model is shown to exhibit a backward bifurcation under certain conditions. Conditions for (...) optimal control of the co-infection are derived using the Pontryagin’s maximum principle. Numerical experimentation on the resulting optimality system is performed. Using the incremental cost-effectiveness ratio, it is observed that combining preventative measures for both diseases is the best strategy for optimal control of HIV-malaria co-infection at the workplace. (shrink)

A simplified model using kinetic logic is proposed to approach the problem after Hepatitis B viral (HBV) infection. It accounts for several stable regimes or attractors corresponding to the essential dynamic behaviour of the replication of the Hepatitis B virus. Infection with the virus can result in viral clearance, fulminant hepatic failure and death, or chronic transmissible infection, that is multistationarity corresponding to the existence of the positive feedback circuit in our modelling. Another implication of this model (...) is the existence of oscillations or homeostatic mechanisms, sometimes observed in the viral cycle, consistent with the existence of the negative feedback circuit. Thus, this report shows how a simple model of kinetic logic may be used to account for the variety of manifestations of HBV infection. This model implies the presence of the Hepatitis B e antigen, whose conservation suggests that it plays an important role in the life cycle of hepadnaviruses. Its function in the viral cycle is still unknown, but our model suggests that this antigen could explain the passage from one state of the viral infection (acute or latent) to another, as well as the oscillatory behavior which may account for the intermittent symptoms of hepatitis observed in some patients. Furthermore, this model shows a virgin state. This state is also reached after recovery. The model proposed demonstrates that starting from a viral acute infection, the host's immune response, depending on the immunological status of the patient, can lead to viral clearance, or to periodic spontaneous reactivation. (shrink)

The human intestines are constantly under the influence of numerous pathological factors: enteropathogenic microorganisms, food antigens, physico‐chemical stress associated with digestion and bacterial metabolism, therefore it must be provided with a system of protection against adverse impact. Recent studies have shown that Paneth cells play a crucial role in maintaining homeostasis of the small intestines. Paneth cells perform many vital functions aimed at maintaining a homeostatic balance between normal microbiota, infectious pathogens and the human body, regulate the qualitative composition and (...) number of intestinal microorganisms, prevent the introduction of potentially pathogenic species, and protect stem cells from damage. Paneth cells take part in adaptive and protective‐inflammatory reactions. Paneth cells maintain dynamic balance between microbial populations, and the macroorganism, preventing the development of intestinal infections and cancer. They play a crucial role in gastrointestinal homeostasis and may be key factors in the etiopathological progression of intestinal diseases. (shrink)

We investigate and analyze the dynamics of hepatitis B with various infection phases and multiple routes of transmission. We formulate the model and then fractionalize it using the concept of fractional calculus. For the purpose of fractionalizing, we use the Caputo–Fabrizio operator. Once we develop the model under consideration, existence and uniqueness analysis will be discussed. We use fixed point theory for the existence and uniqueness analysis. We also prove that the model under consideration possesses a bounded and (...) positive solution. We then find the basic reproductive number to perform the steady-state analysis and to show that the fractional-order epidemiological model is locally and globally asymptotically stable under certain conditions. For the local and global analysis, we use linearization, mean value theorem, and fractional Barbalat’s lemma, respectively. Finally, we perform some numerical findings to support the analytical work with the help of graphical representations. (shrink)

The spread of epidemics, especially COVID-19, is having a significant impact on the world. If an epidemic is not properly controlled at the beginning, it is likely to spread rapidly and widely through the coexistence relationship between natural and social systems. A university community is a special, micro-self-organized social system that is densely populated. However, university authorities in such an environment seem to be less cautious in the defence of an epidemic. Currently, there is almost no quantitative research on epidemic (...) spreading and response strategies in universities. In this paper, a case study of a university community is considered for a simulation of an infection evolving after an epidemic outbreak based on the method of system dynamics of the three stages. The results show the following: By improving the speed of the initial emergency response, the total number of patients can be effectively controlled. A quarantine policy helps to slow down the evolution of infection. The higher the isolation ratio, the higher the cost; therefore, the isolation ratio should be optimized. It is important to make emergency plans for controlling epidemic spreading and carry out emergency drills and assessments regularly. According to the results of this study, we suggest an emergency management framework for public health events in university communities. (shrink)

The main objective of Zika transmission studies is to work out the simplest approach to scale back human mortality and morbidity caused by the disease. Therefore, it is essential to spot the relative importance of the various factors contributing to the transmission and prevalence of the disease. Many mathematical models have been formulated incorporating vector-to-human transmission or human-to-human transmission. However, they do not take into consideration the mixture of both sorts of transmission. It raises the question of the impact of (...) both sorts of transmission on the disease dynamics. We develop a mathematical model of Zika with the vertical transmission in the vector population and human-to-human transmission to answer this question. It includes the immature phase of mosquitoes, adult mosquitoes, and human hosts. Results show that neglecting sexual transmission results in an understatement of the proportion of the infected population. Furthermore, it reduces the speed of disease spreading. On the other hand, vertical transmission in mosquitoes has a negligible effect on the dynamics of disease spread. We perform a sensitivity analysis of the reproductive number R 0 to raise to understand the parameters driving the dynamics of the disease. It appears that the most sensitive parameters in decreasing order are as follows: the adult mosquito death rate, the sting rate, the transmission probability of mosquito to human, and, therefore, the transmission probability of human to mosquito. Furthermore, the proportion at the equilibrium of infected humans is extremely sensitive to the transition rate from the immature vector stage to the adult stage, the human-to-human transmission rate, and, therefore, the human recovery rate. These results confirm that control policies targeting the vector population and, therefore, the recovery rate of people are pretty effective solutions. To validate the model and estimate the important parameters of the model and the prediction of the disease, we consider the real cases in Colombia from 2016. In a series of graphic maps, we presented the comparative study to estimate the disease scenarios and to predict the time limit of the epidemic control measure. (shrink)

Schistosomiasis, a vector-borne chronically debilitating infectious disease, is a serious public health concern for humans and animals in the affected tropical and sub-tropical regions. We formulate and theoretically analyze a deterministic mathematical model with snail and bovine hosts. The basic reproduction number R0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R_0$$\end{document} is computed and used to investigate the local stability of the model’s steady states. Global stability of the endemic equilibrium is carried out by constructing a suitable Lyapunov function. (...) Sensitivity analysis shows that the basic reproduction number is most sensitive to the model parameters related to the contaminated environment, namely: shedding rate of cercariae by snails, cercariae to miracidia survival probability, snails-miracidia effective contact rate and natural death rate of miracidia and cercariae. Numerical results show that when no intervention measures are implemented, there is an increase of the infected classes, and a rapid decline of the number of susceptible and exposed bovines and snails. Effects of the variation of some of the key sensitive model parameters on the schistosomiasis dynamics as well as on the initial disease transmission threshold parameter R0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R_0$$\end{document} are graphically depicted. (shrink)

Malaria is a Plasmodium parasitic disease transmitted by infected female Anopheles mosquitoes. Climatic factors, such as temperature, humidity, rainfall, and wind, have significant effects on the incidence of most vector-borne diseases, including malaria. The mosquito behavior, life cycle, and overall fitness are affected by these climatic factors. This paper presents the results obtained from investigating the optimal control strategies for malaria in the presence of temperature variation using a temperature-dependent malaria model. The study further identified the temperature ranges in four (...) different geographical regions of sub-Saharan Africa, suitable for mosquitoes. The optimal control strategies in the temperature suitable ranges suggest, on average, a high usage of both larvicides and adulticides followed by a moderate usage of personal protection such as bednet. The average optimal bednet usage mimics the solution profile of the mosquitoes as the mosquitoes respond to changes in temperature. Following the results from the optimal control, this study also investigates using a temperature-dependent model with insecticide-sensitive and insecticide-resistant mosquitoes the impact of insecticide-resistant mosquitoes on disease burden when temperature varies. The results obtained indicate that optimal bednet usage on average is higher when insecticide-resistant mosquitoes are present. Besides, the average bednet usage increases as temperature increases to the optimal temperature suitable for mosquitoes, and it decreases after that, a pattern similar to earlier results involving insecticide-sensitive mosquitoes. Thus, personal protection, particularly the use of bednets, should be encouraged not only at low temperatures but particularly at high temperatures when individuals avoid the use of bednets. Furthermore, control and reduction of malaria may be possible even when mosquitoes develop resistance to insecticides. (shrink)

This manuscript considers the transmission dynamics of lymphatic filariasis with some intervention strategies in place. Unlike previously developed models, our model takes into account both the exposed and infected classes in both the human and mosquito populations, respectively. We also consider vaccinated, treated and recovered humans in the presented model. The global dynamics of the proposed model are completely determined by the basic and effective reproduction numbers. We then use Lyapunov function theory to find the sufficient conditions for (...) global stability of both the disease-free equilibrium and endemic equilibrium. The Lyapunov functions show that when the basic reproduction number is less than or equal to unity, the disease-free equilibrium is globally asymptotically stable, and when it is greater than unity then the endemic equilibrium is also globally asymptotically stable. Finally, numerical simulations are carried out to investigate the effects of the intervention strategies and key parameters to the spread of lymphatic filariasis. The numerical simulations support the analytical results and illustrate possible model behavioral scenarios. (shrink)

To date, our knowledge of Rift Valley fever disease spread and maintenance is still limited, as flooding, humid weather and presence of biting insects such as mosquitoes, have not completely explained RVF outbreaks. We propose a model that includes livestock, mosquitoes and ticks compartments structured according to their questing and feeding behaviour in order to study the possible role of ticks on the dynamics of RVF. To quantify disease transmission at the initial stage of the epidemic, we derive an (...) explicit formula of the basic reproductive number, $$R_0$$ R 0. Using the concept of Metzler matrix, we state necessary conditions for global asymptotic stability of the disease-free equilibrium. Results suggest that although host-ticks interactions may serve as disease reservoirs or disease amplifiers, the Aedes reproductive number should be kept under unity if disease post-epizootics activities are to be controlled. Results of both local and global sensitivity analysis of selected model parameters indicate that $$R_0$$ R 0 is more sensitive to the ticks attachment and detachment rates, probability of transmission from ticks to host and from host to ticks, length of infection in livestock and ticks death rate. Furthermore, when comparing the mean value of $$R_0$$ R 0 with that from previous studies which did not include ticks we found that our $$R_0$$ R 0 is very much larger resulting in an increase in the exponential phase of an outbreak. These findings suggest that if ticks are capable of transmitting the virus, they may be contributing to disease outbreaks and endemicity. (shrink)

The occurrence of a new strain of SARS-CoV-2 cannot be ruled out. Therefore, this study seeks to investigate the possible effects of a hypothetical imperfect anti-COVID-19 vaccine on the control of not only the first variant of SARS-CoV-2 but also the second variant of SARS-CoV-2. We further examine the rates and a, escape of quarantined infectious individuals from isolation centers. The control R c and basic reproduction numbers R 0 are computed which gives assess to obtain asymptotic stability of disease-free (...) equilibrium point globally and the existence of a unique persistent equilibrium solution. Numerical results reveal that people infected with the second strain who are vaccinated with an imperfect vaccine are under control but the prevalence of the second variant enhances the prevalence of the first variant. Thus, discovering a vaccine that is effective for the prevention of variant 2 is necessary for the control of COVID-19. Numerical results also reveal that increase in the rate at which individuals infected with the first variant escape the isolation center gives rise to the population infected with the first variant and lowers the peak of the population infected with the second variant. This is probably because individuals infected with the second variant appear to be more careful with their lives and get vaccinated more than individuals infected with the first variant. (shrink)

Sitting on the fine line between pathogen ‘transmissibility’ and ‘severity’, the Behavioural Immune System (BIS) is responsible for activating behaviours that minimise infection risks and maximise fitness. To achieve self-preservation, the BIS also fuels social and political attitudes. We aim to explain societal changes that may be sparked by COVID-19 by highlighting links between human evolutionary history and our psychological faculties mediated by the BIS.

Infections and deaths associated with COVID-19 show a high degree of heterogeneity across different populations. A thorough understanding of population-level predictors of such outcomes is crucial for devising better-targeted and more appropriate public health preparedness measures. While demographic, economic, and health-system capacity have featured prominently in recent work, cultural, and behavioral characteristics have largely been overlooked. However, cultural differences shape both the public policy response and individuals' behavioral responses to the crisis in ways that can impact infection dynamics (...) and key health outcomes. To address this gap, we used meta-analytic methods to explore the global variability of three public health outcomes during the first wave of the pandemic. This set of analyses identified several cultural/behavioral attributes as independent predictors of public health outcomes after adjusting for key demographic, political, economic, and health-system-related predictors; which were robust in sensitivity analyses. In conclusion, this study clearly demonstrates that cultural attributes do in fact account for some of the global disparities in COVID-19-attributed health outcomes. As a consequence, policymakers should more explicitly consider a society's cultural attributes alongside other important parameters such as demographic characteristics and health system constraints in order to develop better tailored and more effective policy responses. (shrink)

This is the first book to systemize all levels of communicative behavior of phages. Phages represent the most diverse inhabitants on this planet. Until today they are completely underestimated in their number, skills and competences and still remain the dark matter of biology. Phages have serious effects on global energy and nutrient cycles. Phages actively compete for host. They can distinguish between ‘self’ and ‘non-self’. They process and evaluate available information and then modify their behaviour accordingly. These diverse competences show (...) us that this capacity to evaluate information is possible owing to communication processes within phages, between the same, related and different phage species, and between phages and non-phage organisms. This is crucial in coordinating infection strategies and recombination in phage genomes. In 22 chapters, expert contributors review current research into the varying forms of phage biocommunication and Phagetherapy. Biocommunication of Phages aims to assess the current state of research, to orient further investigations on how phages communicate with each other to coordinate their behavioral patterns, and to inspire further investigation of the role of non-phage viruses in these highly dynamic interactional networks. (shrink)

Indigenous knowledge is the dynamic information base of a society, facilitating communication and decision-making. It is the cornerstone of many modern-day innovations in science and technology. It is also a ready and valuable resource for sustainable and resilient livelihoods, and attracts increasing public interest due to its applications in bio-technology, health, bioprospecting, pharmaceuticals, agriculture, food preparation, mathematics and astronomy. INDIGENOUS KNOWLEDGE OF NAMIBIA is a fascinating compendium aimed at a wide readership of academics and students, government officials, policy makers, and (...) development partners. The 17 chapters examine the indigenous knowledge of medicinal plants for treating HIV/AIDS, malaria, cancer, and other microbial infections of humans and livestock; indigenous foods; coping and response strategies in dealing with human-wildlife conflicts, floods, gender, climate change and the management of natural resources. A new rationalisation of adolescent customary and initiation ceremonies is recommended in response to the HIV/AIDS pandemic; and a case study of the San people of Namibia speaks to the challenges of harmonising modern education with that of indigenous people. (shrink)

The rapid dynamics of COVID-19 calls for quick and effective tracking of virus transmission chains and early detection of outbreaks, especially in the “phase 2” of the pandemic, when lockdown and other restriction measures are progressively withdrawn, in order to avoid or minimize contagion resurgence. For this purpose, contact-tracing apps are being proposed for large scale adoption by many countries. A centralized approach, where data sensed by the app are all sent to a nation-wide server, raises concerns about citizens’ (...) privacy and needlessly strong digital surveillance, thus alerting us to the need to minimize personal data collection and avoiding location tracking. We advocate the conceptual advantage of a decentralized approach, where both contact and location data are collected exclusively in individual citizens’ “personal data stores”, to be shared separately and selectively, voluntarily, only when the citizen has tested positive for COVID-19, and with a privacy preserving level of granularity. This approach better protects the personal sphere of citizens and affords multiple benefits: it allows for detailed information gathering for infected people in a privacy-preserving fashion; and, in turn this enables both contact tracing, and, the early detection of outbreak hotspots on more finely-granulated geographic scale. The decentralized approach is also scalable to large populations, in that only the data of positive patients need be handled at a central level. Our recommendation is two-fold. First to extend existing decentralized architectures with a light touch, in order to manage the collection of location data locally on the device, and allow the user to share spatio-temporal aggregates—if and when they want and for specific aims—with health authorities, for instance. Second, we favour a longer-term pursuit of realizing a Personal Data Store vision, giving users the opportunity to contribute to collective good in the measure they want, enhancing self-awareness, and cultivating collective efforts for rebuilding society. (shrink)

Throughout the Covid-19 pandemic, people have been eager to learn what factors, and especially what public health policies, cause infection rates to wax and wane. But figuring out conclusively what causes what is difficult in complex systems with nonlinear dynamics, such as pandemics. We review some of the challenges that scientists have faced in answering quantitative causal questions during the Covid-19 pandemic, and suggest that these challenges are a reason to augment the moral dimension of conversations about causal (...) inference. We take a lesson from Martha Nussbaum—who cautions us not to think we have just one question on our hands when we have at least two—and apply it to modeling for causal inference in the context of cost-benefit analysis. (shrink)

BackgroundThe outbreak of COVID-19 has been a major interrupting event, challenging how societies and individuals deal with risk. An essential determinant of the virus’ spread is a series of individual decisions, such as wearing face masks in public space. Those decisions depend on trade-offs between costs and risks, and beliefs are key to explain these.MethodsWe elicit beliefs about the COVID-19 pandemic during lockdown in France by means of surveys asking French citizens about their belief of the infection fatality ratio (...) for COVID-19, own risk to catch the disease, risk as perceived by others, and expected prevalence rate. Those self-assessments were measured twice during lockdown: about 2 weeks after lockdown started and about 2 weeks before lockdown ended. We also measured the quality of these beliefs with respect to available evidence at the time of the surveys, allowing us to assess the calibration of beliefs based on risk-related socio-demographics. Finally, comparing own risk to expected prevalence rates in the two successive surveys provides a dynamic view of comparative optimism with respect to the disease.ResultsThe risk perceptions are rather high in absolute terms and they increased between the two surveys. We found no evidence for an impact of personal experience with COVID-19 on beliefs and lower risk perceptions of the IFR when someone in the respondent’s family has been diagnosed with a disease. Answers to survey 1 confirmed this pattern with a clear indication that respondents were optimistic about their chances to catch COVID-19. However, in survey 2, respondents revealed comparative pessimism.ConclusionThe results show that respondents overestimated the probabilities to catch or die from COVID-19, which is not unusual and does not necessarily reflect a strong deviation from rational behavior. While a rational model explains why the own risk to catch COVID-19 rose between the two surveys, it does not explain why the subjective assessment of the IFR remained stable. The comparative pessimism in survey 2 was likely due to a concomitant increase in the respondents’ perceived chances to catch the disease and a decreased expected prevalence rate. (shrink)

This article argues that the fact that an action will compound a prior injustice counts as a reason against doing the action. I call this reason The Anti-Compounding Injustice principle or aci. Compounding injustice and the aci principle are likely to be relevant when analyzing the moral issues raised by “big data” and its combination with the computational power of machine learning and artificial intelligence. Past injustice can infect the data used in algorithmic decisions in two distinct ways. Sometimes prior (...) injustice undermines the accuracy of the data itself. In these contexts, improving accuracy will also help to avoid compounding injustice. Other times, past injustice produces real-world differences among people with regard to skills, health, wealth, and other traits that employers, lenders, and others seek to measure. When decisions are based on accurate data that itself results from prior injustice, these decisions can also compound injustice. This second dynamic has received less attention than the first but is especially important because improving the accuracy of data will not mitigate this unfairness. (shrink)

In response to the ubiquitous graphs and maps of COVID-19, artists, designers, data scientists, and public health officials are teaming up to create counter-plots and subaltern maps of the pandemic. In this intervention, we describe the various functions served by these projects. First, they offer tutorials and tools for both dataviz practitioners and their publics to encourage critical thinking about how COVID-19 data is sourced and modeled—and to consider which subjects are not interpellated in those data sets, and why not. (...) Second, they demonstrate how the pandemic’s spatial logics inscribe themselves in our immediate material landscapes. And third, they remind us of our capacity to personalize and participate in the creation of meaningful COVID visualizations—many of which represent other scales and dimensions of the pandemic, especially the quarantine quotidian. Together, the official maps and counter-plots acknowledge that the pandemic plays out differently across different scales: COVID-19 is about global supply chains and infection counts and TV ratings for presidential press conferences, but it is also about local dynamics and neighborhood mutual aid networks and personal geographies of mitigation and care. (shrink)

Background Ethical conflict is a problem with negative consequences, which can compromise the quality and ethical standards of the nursing profession and it is a source of stress for health care practitioners’, especially for nurses. Objectives The main aim of this study was to analyze Spanish critical care nurses’ level of exposure to ethical conflict and its association with sociodemographic, occupational, and COVID-19–related variables. Research Design, Participants, and Research context: This was a quantitative cross-sectional descriptive study conducted among 117 nurses (...) working in critical care units. Data collection tools were sociodemographic, occupational, and COVID-19–related questionnaires and previously validated Spanish version of Ethical Conflict in Nursing Questionnaire-Critical Care Version. Ethical Considerations We obtained permission from the Ethics Committee and participants' informed consent. Findings Data indicates a moderate level of exposure to ethical conflicts. The most frequent ethical conflicts were related to situations about "treatment and clinical procedures." The most intensity of ethical conflicts was related to situations about "treatment and clinical procedures" and "dynamics of the service and working environment." No statistical significance was identified between the socio-demographic variables and level of exposure to ethical conflicts. However, for critical care nurses working in ICU, nurses with perceived worked stress had a higher level of exposure to ethical conflicts. Likewise, critical care nurses whose family/friends were infected with COVID-19 had a higher level of exposure. Conclusions Critical care nurses experience a moderate level of exposure to ethical conflicts which is consistent with the results of previous studies. A deeper understanding of ethical conflicts in conflictive situations allows recognition of the situations that occur in everyday clinical practice, identification of the ethical conflicts, and facilitation of the nurses working in the challenging clinical situation. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Philosophy and Literature 27.2 (2003) 284-303 [Access article in PDF] Accidental Art:Tolstoy's Poetics of Unintentionality Michael A. Denner I ART'S ABILITY TO INFECT another with an emotion, the concept that has come to be probably the most readily identified catchphrase in What Is Art? (though it crops up in his earlier writings on art), derives from L. N. Tolstoy's dynamic identity claim about art: we know an artist has (...) created a genuine work of art when he "hands on to others feelings he has lived through, and that others are infected by these feelings and also experience them." 1 "What is art?" is then a taxonomical question, and, according to Tolstoy, art is identifiable from non-art not by some set of external characteristics—the way, say, Aristotle categorized animals in his natural history—rather art is recognizable by its function, by what it does. In this sense art is like a tool: A given thing is art because it performs a certain task, much as one might claim a screwdriver is anything that sets and removes screws, regardless of its external characteristics. Tolstoy, in fact, repeatedly refers to art as "orudie," "a tool," or even "a weapon."It is worth noting from the outset that this metaphor of contagiousness is one of sublimated violence. For its passive "perceiver" (Tolstoy's characteristic term for the consumer of art), art amounts to irresistible, surreptitious emotional manipulation by an external entity. Tolstoy is ever attentive to the underlying meanings of the words he chooses, and I think he means to emphasize the latent, etymological meaning of the zarazit', to infect, the root of which is razit', to strike, a military term that likely resonated with Tolstoy, a war veteran. 2 Etymological arguments aside, Tolstoy makes explicit the psychological violation that goes hand-in-hand [End Page 284] with the experience of a work of art in a diary entry from a period of work on an earlier variant of What Is Art?: "One must hone the artistic work so that it penetrates. To hone a work means to make it perfect artistically, in which case it will pierce through the indifference...." 3 In an earlier version of the essay, Tolstoy offers "hypnotism" as a synonym for infection (p. 53).With its ability to "penetrate" through indifference and colonize, willy-nilly, the other, art accomplishes directly and immediately what no amount of rational argument could accomplish: "Art is differentiated from the activity of rational activity, which demands preparation and a certain sequence of knowledge (so that one cannot learn trigonometry before knowing geometry), by the fact that it acts on people independently of their state of development and education, that the charm of a picture, of sounds, or of forms, infects any man whatever his plane of development" (p. 178).The effect of art does not depend on some graduated, sequential process as it does for rational activity: art's infectiousness is immediate and irresistible. According to What Is Art?, the summum bonum of art's infectiousness, its best use, but notably not its only, is bringing about the Kingdom of God by effecting a change in the psychology of all the individuals who experience it. "Religious art," Tolstoy's supreme category of art, surmounts the (ultimately illusory for Tolstoy) individuality of the perceiver by inducing in him or her an emotional union with the artist and all others who have experienced the work of art, thereby inducting all perceivers into the universal collective of humankind: "In this freeing of our personality from its separation from other people, from its isolation, in this uniting of personality with others, lies the chief characteristic and the great attractive force of art" (p. 228). Art is a sacrament and the artist a priest of sorts.It is often said, even by those who have read the work, that Tolstoy "rejected" art in the last decades of his life, and What Is Art? is often cited as evidence. Granted, much of the book excoriates much of the art of the ages, but one must not... (shrink)

In lieu of an abstract, here is a brief excerpt of the content:The “Wider View”: André Hellegers’s Passionate, Integrating Intellect and the Creation of BioethicsWarren Thomas Reich* (bio)AbstractThis article provides an account of how André Hellegers, founder and first Director of the Kennedy Institute of Ethics at Georgetown University, laid medicine open to bioethics. Hellegers’s approach to bioethics, as to morality generally and also to medicine and biomedical science, involved taking the “wider view”—a value-filled vision that integrated and gave meaning (...) to what otherwise was disparate, precarious, and conflicting. This article shows how Hellegers’s wider view of bioethics was shaped by events in his own life, his resultant sense of the precariousness of life and health, his commitment to religious inclusiveness, his research in fetal medicine, his clinical experience in obstetrics, his role in the struggle to change the teaching of the Roman Catholic Church on fertility control, and his developing concepts of health and disease. Hellegers was committed to and worked toward bioethics as a self-consciously interdisciplinary field in which the contributing disciplines adapt to each other—rather than sustain themselves as autonomous disciplines—to create a dynamic and complex intellectual, clinical, and social activity.André Hellegers’s personality and life were like that of a meteor: brief appearance on the scene; high-speed, flaming trajectory; quick burn-out; its smallest residue worth examining for ages to come. You had to watch carefully, for otherwise you might miss what he was about—what he was really about. He had an unusually probing and unflagging mind, coupled with the ability to make people think; and in a very real sense, that is what he was always about. André was an extremely effective communicator. He was like Fred Astaire: he had flair and charm, and no matter how crowded the room, you instantly knew when he entered it. Like Astaire, he had a deep intensity and striving for perfection while making his art always look like great fun. He was an engaging [End Page 25] story-teller who also knew how to stun intelligent people with his insightful, often ironic and humorous thinking that got to the bottom of things very quickly, leaving his interlocutors with a huge agenda for further reflection. Yet in spite of all this alluring talent, André never attracted attention to himself in a vain way. Even as raconteur, he was always working, getting people to think and talk.There were three great passions in Hellegers’s life that enabled him to inspire and shape bioethics as he did. He had a passionate intellect that was constantly probing for new clarity at new levels of understanding and values, and he had the ability to infect other people with his intellectual passion. André Hellegers was deeply rooted in a Catholicism scarcely imaginable in the United States—an open, historically-conscious, northern European faith that kept him free of ideology while providing him a foundation on which he built a rich ecumenicity of theological and philosophical bioethics. Finally, and perhaps most decisively for his founding work in bioethics, Hellegers pushed and probed to get a world that was almost totally unaccustomed to communicating over disciplinary lines (incredibly, virtually no interdisciplinary conferences had taken place before his day) to dialogue and collaborate across the barriers of medicine, politics, and religion.IntroductionThe customary way of writing a history of someone’s involvement in the origins of something—say, the origins of a nation or, I suppose, the origins of bioethics—certainly would not customarily start with the foregoing type of vignette. It would have as its purpose to discuss such things as issues, events that raised issues, methods pursued and applied, and outcomes achieved. However, in this modest account of some of the major contributions of the late André E. Hellegers, M.D., to the development of the field of bioethics, I intend to focus on a different level of historical inquiry, one that portrays and explains the person, his world-view, and his motivation, as well as the cultural forces and events that conspired to make Hellegers and the people with whom he came into contact vibrant with a sense of innovative and creative—not to mention urgent—inquiry. I believe that... (shrink)

The susceptible-transmissible-removed (STR) model is a deterministic compartment model, based on the susceptible-infected-removed (SIR) prototype. The STR replaces 2 SIR assumptions. SIR assumes that the emigration rate (due to death or recovery) is directly proportional to the infected compartment’s size. The STR replaces this assumption with the biologically appropriate assumption that the emigration rate is the same as the immigration rate one infected period ago. This results in a unique delay differential equation epidemic model with the delay equal to the (...) infected period. Hamer’s mass action law for epidemiology is modified to resemble its chemistry precursor—the law of mass action. Constructing the model for an isolated population that exists on a surface bounded by the extent of the population’s movements permits compartment density to replace compartment size. The STR reduces to a SIR model in a timescale that negates the delay—the transmissible timescale. This establishes that the SIR model applies to an isolated population in the disease’s transmissible timescale. Cyclical social interactions will define a rhythmic timescale. It is demonstrated that the geometric mean maps transmissible timescale properties to their rhythmic timescale equivalents. This mapping defines the hybrid incidence (HI). The model validation demonstrates that the HI-STR can be constructed directly from the disease’s transmission dynamics. The basic reproduction number (R0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathcal{R}}_0$$\end{document}) is an epidemic impact property. The HI-STR model predicts that R0∝ρnB\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathcal{R}}_0 \propto \root \mathfrak{B} \of {\rho_n}$$\end{document} where ρn\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\rho_n$$\end{document} is the population density, and B\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathfrak{B}}$$\end{document} is the ratio of time increments in the transmissible- and rhythmic timescales. The model is validated by experimentally verifying the relationship. R0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathcal{R}}_0$$\end{document}’s dependence on ρn\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\rho_n$$\end{document} is demonstrated for droplet-spread SARS in Asian cities, aerosol-spread measles in Europe and non-airborne Ebola in Africa. (shrink)

A two strain HIV/AIDS model with treatment which allows AIDS patients with sensitive HIV-strain to undergo amelioration is presented as a system of non-linear ordinary differential equations. The disease-free equilibrium is shown to be globally asymptotically stable when the associated epidemic threshold known as the basic reproduction number for the model is less than unity. The centre manifold theory is used to show that the sensitive HIV-strain only and resistant HIV-strain only endemic equilibria are locally asymptotically stable when the associated (...) reproduction numbers are greater than unity. Qualitative analysis of the model including positivity, boundedness and persistence of solutions are presented. The model is numerically analysed to assess the effects of treatment with amelioration on the dynamics of a two strain HIV/AIDS model. Numerical simulations of the model show that the two strains co-exist whenever the reproduction numbers exceed unity. Further, treatment with amelioration may result in an increase in the total number of infective individuals (asymptomatic) but results in a decrease in the number of AIDS patients. Further, analysis of the reproduction numbers show that antiretroviral resistance increases with increase in antiretroviral use. (shrink)

Autonomous transposable elements, generally considered as junk and selfish, encode transposition proteins that can bind, copy, break, join or degrade nucleic acids as well as process or interact with other proteins. Such a repertoire of activities might be of interest for the host cell. There is indeed substantial evidence that mobile DNA can serve as a dynamic reservoir for new cellular functions. Transposable element genes encoding transposase, integrase, reverse transcriptase as well as structural and envelope proteins have been repeatedly recruited (...) by their host during evolution in most eukaryotic lineages. Such domesticated sequences protect us against infections, are necessary for our reproduction, allow the replication of our chromosomes and control cell proliferation and death; others are essential for plant development. Many new candidates for domesticated sequences have been revealed by sequencing projects. Their functional analysis will uncover new aspects of evolutionary alchemy, the turning of junk into gold within genomes. BioEssays 28: 913–922, 2006. © 2006 Wiley periodicals, Inc. (shrink)