Livestock transportation is a key factor that contributes to the spatial spread of brucellosis.To analyze the impact of sheep transportation on brucellosis transmission,we develop a human–sheep coupled brucellosis mo...Livestock transportation is a key factor that contributes to the spatial spread of brucellosis.To analyze the impact of sheep transportation on brucellosis transmission,we develop a human–sheep coupled brucellosis model within a metapopulation network framework.Theoretically,we examine the positively invariant set,the basic reproduction number,the existence,uniqueness,and stability of disease-free equilibrium and the existence of the endemic equilibrium of the model.For practical application,using Heilongjiang province as a case study,we simulate brucellosis transmission across 12 cities based on data using three network types:the BA network,the ER network,and homogeneous mixing network.The simulation results indicate that the network's average degree plays a role in the spread of brucellosis.For BA and ER networks,the basic reproduction number and cumulative incidence of brucellosis stabilize when the network's average degree reaches 4 or 5.In contrast,sheep transport in a homogeneous mixing network accelerates the cross-regional spread of brucellosis,whereas transportation in a BA network helps to control it effectively.Furthermore,the findings suggest that the movement of sheep is not always detrimental to controlling the spread of brucellosis.For cities with smaller sheep populations,such as Shuangyashan and Qitaihe,increasing the transport of sheep outward amplifies the spatial spread of the disease.In contrast,in cities with larger sheep populations,such as Qiqihar,Daqing,and Suihua,moderate sheep outflow can help reduce the spread.In addition,cities with large livestock populations play a dominant role in the overall transmission dynamics,underscoring the need for stricter supervision in these areas.展开更多
We investigate the stochastic resonance （SR） phenomenon induced by the periodic signal in a metapopulation system with colored noises. The analytical expression of signal-to-noise is derived in the adiabatic limit. ...We investigate the stochastic resonance （SR） phenomenon induced by the periodic signal in a metapopulation system with colored noises. The analytical expression of signal-to-noise is derived in the adiabatic limit. By numerical calculation, the effects of the addictive noise intensity, the multiplicative noise intensity and two noise self-correlation times on SNR are respectively discussed. It shows that： （i） in the case that the addictive noise intensity M takes a small value, a SR phenomenon for the curve of SNR appears; however, when M takes a large value, SNR turns into a monotonic function on the multiplicative noise intensity Q. （ii） The resonance peaks in the plots of the multiplicative noise intensity Q versus its self-correlation time Vl and the addictive noise intensity M versus its self-correlation time ~2 translate in parallel. Mean- while, a parallel translation also appears in the plots of vl versus Q and v2 versus M. （iii） The interactive effects between self-correlation times Vl and v2 are opposite.展开更多
Hydrobiidae is one of the most diverse taxa among limnic and estuarine mollusks. Patterns of spatial and seasonal distribution of Heleobia australis were studied in ten stations over two years, in the urban eutrophic ...Hydrobiidae is one of the most diverse taxa among limnic and estuarine mollusks. Patterns of spatial and seasonal distribution of Heleobia australis were studied in ten stations over two years, in the urban eutrophic bay of Guanabara, Rio de Janeiro, Brazil. Spatial dispersal strategies in adults of this species, analyzed in the laboratory, revealed three patterns: 1) mobility on soft sediments;2) mobility on hard substrata;and 3) the ability to lift from the bottom to the surface, to again sink down. This facilitate species movement from one location to another by surface currents or attached to floating debris. Thus, individuals are able to escape from an impacted area and further re-colonize other patches after recovering from local impacts. The hypothesis of metapopulation dynamics (source– sink) was analyzed. Two stations with high and constant numbers of individuals were grouped and tested as possible ‘sources’. The number of specimens in the remaining stations was highly variable, even with the complete disappearance and posterior highly dense re-occurrence of the mollusk, whereby these were tested as possible ‘sinks’. Results derived from nested ANOVA supported the hypothesis of metapopulation dynamics in the case of H. australis adults, ex-pressed through opportunistic-species domi- nation of a highly impacted estuarine system, such as Guanabara Bay.展开更多
The research on spatial epidemic models is a topic of considerable recent interest. In another hand, the advances in computer technology have stimulated the development of stochastic models. Metapopulation models are ...The research on spatial epidemic models is a topic of considerable recent interest. In another hand, the advances in computer technology have stimulated the development of stochastic models. Metapopulation models are spatial designs that involve movements of individuals between distinct subpopulations. The purpose of the present work has been to develop stochastic models in order to study the transmission dynamics and control of infectious diseases in metapopulations. The authors studied Susceptible-Infected-Susceptible （SIS） and Susceptible-lnfected-Recovered （SIR） epidemic schemes, using the Gillespie algorithm, Computational numerical simulations were carried in order to explore the models. The results obtained show how the dynamics of transmission and the application of control measures within each subpopulation may affect all subpopulations of the system. They also show how the distribution of control measures among subpopulations affects the efficacy of these strategies. The dynamics of the stochastic models developed in the current study follow the trends observed in the classic deterministic designs. Also, the present models exhibit fluctuating behavior. This work highlights the importance of the spatial distribution of the population in spread and control of infectious diseases. In addition, it shows how chance could play an important role in these scenarios.展开更多
Objective: To verify phylogeography and genetic structure of Acanthamoeba populations among the Iranian clinical isolates and natural/artificial environments distributed in various regions of the country.Methods: We s...Objective: To verify phylogeography and genetic structure of Acanthamoeba populations among the Iranian clinical isolates and natural/artificial environments distributed in various regions of the country.Methods: We searched electronic databases including Medline, Pub Med, Science Direct, Scopus and Google Scholar from 2005 to 2016. To explore the genetic variability of Acanthamoeba sp, 205 sequences were retrieved from keratitis patients, immunosuppressed cases and environmental sources as of various geographies of Iran.Results: T4 genotype was the predominant strain in Iran, and the rare genotypes belonged to T2, T3, T5(Acanthamoeba lenticulata), T6, T9, T11, T13 and T15(Acanthamoeba jacobsi).A total of 47 unique haplotypes of T4 were identified. A parsimonious network of the sequence haplotypes demonstrated star-like feature containing haplogroups IR6(34.1%) and IR7(31.2%) as the most common haplotypes. In accordance with the analysis of molecular variance, the high value of haplotype diversity(0.612–0.848) of Acanthamoeba T4 represented genetic variability within populations. Neutrality indices of the 18 S ribosomal RNA demonstrated negative values in all populations which represented a considerable divergence from neutrality. The majority of genetic diversity belonged to the infected contact lens and dust samples in immunodeficiency and ophthalmology wards, which indicated potential routes for exposure to a pathogenic Acanthamoeba sp. in at-risk individuals. A pairwise fixation index(FST) was from low to high values(0.024 33–0.418 92). The statistically FST points out that T4 is genetically differentiated between north-west, north-south and centralsouth metapopulations, but not differentiated between west-central, west-south, centralsouth, and north-central isolates.Conclusions: An occurrence of IR6 and IR7 displays that possibly a gene flow of Acanthamoeba T4 occurred after the founder effect or bottleneck experience through ecological changes or host mobility. This is the first systematic review and meta-analysis providing new approaches into gene migration and transmission patterns of Acanthamoeba sp, and targeting at the high-risk individuals/sources among the various regions of Iran.展开更多
The simplified incidence function model which is driven by the colored correlated noises is employed to investigate the extinction time of a metapopulation perturbed by environments. The approximate Fokker-Planck Equa...The simplified incidence function model which is driven by the colored correlated noises is employed to investigate the extinction time of a metapopulation perturbed by environments. The approximate Fokker-Planck Equation and the mean first passage time which denotes the extinction time （Tex） are obtained by virtue of the Novikov theorem and the Fox approach. After introducing a noise intensity ratio and a dimensionless parameter R = D /α （D and a are the multiplicative and additive colored noise intensities respectively）, and then performing numerical computations, the results indicate that： （i） The absolute value of correlation strength A and its correlation time τ3 play opposite roles on the Tex; （ii） For the case of 0 〈λ〈 1,α and its correlation time τ2 play opposite roles on the Tex in which R〉 1 is the best condition, and there is one-peak structure on the Tex - D plot; （iii） For the case of-1 〈 λ≤ 0, D and its correlation time τ1 play opposite roles on the Tex in which R 〈 1 is the best condition and there is one-peak structure on the Tex - τ2 plot.展开更多
We propose a metapopulation model with two geographical scales. In a regional scale, the model describes the dynamics of a collection of habitats connected by migratory movements. In a local scale, we consider some gr...We propose a metapopulation model with two geographical scales. In a regional scale, the model describes the dynamics of a collection of habitats connected by migratory movements. In a local scale, we consider some granularity within each habitat, in the sense that each habitat is itself a collection of patches linked by dispersal. The whole ensemble can be seen as a metapopulation composed by local metapopulations. We analyze the synchronization of the model in the two geographical scales. We present an analytic criterion for synchronization where only the habitats in the regional scale evolve with the same dynamics. Through numerical simulations, we discuss the different synchronization modes. It depends on how the individuals are distributed in the local patches that compose a habitat after migration takes place in the regional scale.展开更多
Emerging infectious diseases and climate change are two of the major challenges in 21st century.Although over the past decades,highly-resolved mathematical models have contributed in understanding dynamics of infectio...Emerging infectious diseases and climate change are two of the major challenges in 21st century.Although over the past decades,highly-resolved mathematical models have contributed in understanding dynamics of infectious diseases and are of great aid when it comes to finding suitable intervention measures,they may need substantial computational effort and produce significant CO_(2) emissions.Two popular modeling approaches for mitigating infectious disease dynamics are agent-based and population-based models.Agent-based models(ABMs)offer a microscopic view and are thus able to capture heterogeneous human contact behavior and mobility patterns.However,insights on individual-level dynamics come with high computational effort that scales with the number of agents.On the other hand,population-based models(PBMs)using e.g.ordinary differential equations(ODEs)are computationally efficient even for large populations due to their complexity being independent of the population size.Yet,population-based models are restricted in their granularity as they assume a(to some extent)homogeneous and well-mixed population.To manage the trade-off between computational complexity and level of detail,we propose spatial-and temporal-hybrid models that use ABMs only in an area or time frame of interest.To account for relevant influences to disease dynamics,e.g.,from outside,due to commuting activities,we use population-based models,only adding moderate computational costs.Our hybridization approach demonstrates significant reduction in computational effort by up to 98%–without losing the required depth in information in the focus frame.The hybrid models used in our numerical simulations are based on two recently proposed models,however,any suitable combination of ABM and PBM could be used,too.Concluding,hybrid epidemiological models can provide insights on the individual scale where necessary,using aggregated models where possible,thereby making a contribution to green computing.展开更多
The COVID-19 pandemic has had a tremendous impact on the transportation and tourism sectors.As vaccines were being administered and lockdowns implemented,owing to the significant social and economic impacts,travel bub...The COVID-19 pandemic has had a tremendous impact on the transportation and tourism sectors.As vaccines were being administered and lockdowns implemented,owing to the significant social and economic impacts,travel bubbles were proposed as a gradual and intermediate open policy to balance risks and economic recovery.However,the travel bubble framework and associated costs and benefits were not well-established during policy implementation.In this study,we propose a travel bubble transportation framework using a metapopulation epidemic and mobility model,and conduct a cost-benefit analysis for the decision-making process during the border reopening phase.Our model focuses on the control of domestic and international long-distance travel inside the bubble to maximize monetary returns derived from tourism benefits and pandemic costs.A sequential decision problem is proposed to make multiple decisions based on real-time observations.We conduct a case study on travel bubbles in Australia,New Zealand,and Japan to test the feasibility of the model.The simulation results show that controlled intra-bubble transportation can generate positive economic benefits while keeping the epidemic within an acceptable range of control.Our framework can assist policymakers in making informed,open decisions by considering multiple attributes during a global pandemic.展开更多
Rocky Mountain spotted fever(RMSF)is a fatal tick-borne zoonotic disease that has emerged as an epidemic in western North America since the turn of the 21st century.Along the US south-western border and across norther...Rocky Mountain spotted fever(RMSF)is a fatal tick-borne zoonotic disease that has emerged as an epidemic in western North America since the turn of the 21st century.Along the US south-western border and across northern Mexico,the brown dog tick,Rhipicephalus sanguineus,is responsible for spreading the disease between dogs and humans.The widespread nature of the disease and the ongoing epidemics contrast with historically sporadic patterns of the disease.Because dogs are amplifying hosts for the Rickettsia rickettsii bacteria,transmission dynamics between dogs and ticks are critical for understanding the epidemic.In this paper,we developed a compartment metapopulation model and used it to explore the dynamics and drivers of RMSF in dogs and brown dog ticks in a theoretical region in western North America.We discovered that there is an extended lag—as much as two years—between introduction of the pathogen to a naïve population and epidemic-level transmission,suggesting that infected ticks could disseminate extensively before disease is detected.A single large city-size population of dogs was sufficient to maintain the disease over a decade and serve as a source for disease in surrounding smaller towns.This model is a novel tool that can be used to identify high risk areas and key intervention points for epidemic RMSF spread by brown dog ticks.展开更多
India has been the latest global epicenter for COVID-19,a novel coronavirus disease that emerged in China in late 2019.We present a base mathematical model for the transmission dynamics of COVID-19 in India and its ne...India has been the latest global epicenter for COVID-19,a novel coronavirus disease that emerged in China in late 2019.We present a base mathematical model for the transmission dynamics of COVID-19 in India and its neighbor,Pakistan.The base model was rigorously analyzed and parameterized using cumulative COVID-19 mortality data from each of the two countries.The model was used to assess the population-level impact of the control and mitigation strategies implemented in the two countries(notably non-pharmaceutical interventions).Numerical simulations of the basic model indicate that,based on the current baseline levels of the control and mitigation strategies implemented,the pandemic trajectory in India is on a downward trend.This downward trend will be reversed,and India will be recording mild outbreaks,if the control and mitigation strategies are relaxed from their current levels.By early September 2021,our simulations suggest that India could record up to 460,000 cumulative deaths under baseline levels of the implemented control strategies,while Pakistan(where the pandemic is comparatively milder)could see over 24,000 cumulative deaths at current mitigation levels.The basic model was extended to assess the impact of back-and-forth mobility between the two countries.Simulations of the resulting metapopulation model show that the burden of the COVID-19 pandemic in Pakistan increases with increasing values of the average time residents of India spend in Pakistan,with daily mortality in Pakistan peaking in mid-August to mid-September of 2021.Under the respective baseline control scenarios,our simulations show that the backand-forth mobility between India and Pakistan could delay the time-to-elimination of the COVID-19 pandemic in India and Pakistan to November 2022 and July 2022,respectively.展开更多
According to investigation on two species of melitaeine butterflies in Yanjiaping Village, Chicheng County, Hebei Province, China, between 1998—2002, to-gether with the use of 1︰10000 contour map of the local area, ...According to investigation on two species of melitaeine butterflies in Yanjiaping Village, Chicheng County, Hebei Province, China, between 1998—2002, to-gether with the use of 1︰10000 contour map of the local area, some conclusions are shown by the SPSS and GIS analysis of data obained from GPS: (1) The two species of melitaeine butterflies have different metapopulation struc-tures. M. phoebe is a source-sink metapopulation, while E. aurinia is a classical metapopulation, supporting the analytic result from our former genetic research. (2) The two species of melitaeine butterflies exhibit different trends of popula-tion dynamics. M. phoebe source-sink metapopulation is very unsteady, and is always small, thus has a tendency to go ex-tinct gradually. But E. aurinia classical metapopulation is stable, and has maintained a larger population size. There-fore, it stands a better chance of long-term survival. (3) The two species of melitaeine butterflies are significantly related in both patch occupancy and local population size. (4) The effect of isolation is significant on the metapopulations of these two species of melitaeine butterflies, consistent with the classical theories, whereas the effect of patch area is not sig-nificant on the metapopulations of these two species of meli-taeine butterflies, which is inconsistent with the classical theories. Therefore, other factors, such as habitat quality, should be considered for their influences on metapopula-tions.展开更多
This article discusses the influence of phenology-related intraseasonal asynchrony on metapopulation dynamics and stability. As the part played by intraseasonal asynchrony is as yet unclear and poorly described, great...This article discusses the influence of phenology-related intraseasonal asynchrony on metapopulation dynamics and stability. As the part played by intraseasonal asynchrony is as yet unclear and poorly described, greater account of it should be taken in both metapopulation research and conservation practice. The subpopulations of the Parnassius mnemosyne metapopulation studied here are strongly isolated because of the phenological shift between them, despite the relatively small physical distances between them. This isolation is the result of a significant temporal shift in the species' flight periods in the main metapopulation centers: in som e seasons its flight times in the different subpopulations did not overlap at all. The predicted results of such strong intraseasonal asynchrony are not altogether clear. On the one hand, they reduce the vulnerability of the entire metapopulation to the effects of short-term random disasters. On the other, the ever-greater isolation of subpopulations may cause the metapopulation to becom e a nonequilibrium one, which will have a serious impact on its long-term survival.展开更多
The spread of methicillin-resistant strains of Staphylococcus aureus(MRSA)in health-care settings has become increasingly difficult to control and has since been able to spread in the general community.The prevalence ...The spread of methicillin-resistant strains of Staphylococcus aureus(MRSA)in health-care settings has become increasingly difficult to control and has since been able to spread in the general community.The prevalence of MRSA within the general public has caused outbreaks in groups of people in close quarters such as military barracks,gyms,daycare centres and correctional facilities.Correctional facilities are of particular importance for spreading MRSA,as inmates are often in close proximity and have limited access to hygienic products and clean clothing.Although these conditions are ideal for spreading MRSA,a recent study has suggested that recurrent epidemics are caused by the influx of colonized or infected individuals into the correctional facility.In this paper,we further investigate the effects of community dynamics on the spread of MRSA within the correctional facility and determine whether recidivism has a significant effect on disease dynamics.Using a simplified hotspot model ignoring disease dynamics within the correctional facility,as well as two metapopulation models,we demonstrate that outbreaks in correctional facilities can be driven by community dynamics even when spread between inmates is restricted.We also show that disease dynamics within the correctional facility and their effect on the outlying community may be ignored due to the smaller size of the incarcerated population.This will allow construction of simpler models that consider the effects of many MRSA hotspots interacting with the general community.It is suspected that the cumulative effects of hotspots for MRSA would have a stronger feedback effect in other community settings.展开更多
Two stochastic models are derived for a susceptible-infectious-susceptible epidemic spreading through a metapopulation： a continuous time Markov chain （CTMC） model and an It6 stochastic differential equation （SDE...Two stochastic models are derived for a susceptible-infectious-susceptible epidemic spreading through a metapopulation： a continuous time Markov chain （CTMC） model and an It6 stochastic differential equation （SDE） model. The stochastic models are numerically compared. Close agreement suggests that computationally intense CTMC simulations can be approximated by simpler SDE simulations. Differential equations for the moments of the SDE probability distribution are also derived, the steady states are solved numerically using a moment closure technique, and these results are compared to simulations. The moment closure technique only coarsely approximates simulation results. The effect of model parameters on stability of the disease-free equilibrium is also numerically investigated.展开更多
Behavioral research has long had an important role in the conservation of terns （Ayes： Stemidae）. Habitat management and restoration of breeding colony sites depends on knowledge of the cues used to select colony a...Behavioral research has long had an important role in the conservation of terns （Ayes： Stemidae）. Habitat management and restoration of breeding colony sites depends on knowledge of the cues used to select colony and nest sites. For example, conspecific attraction with playback and decoys is commonly used to bring terns to suitable colony sites and habitat modification is often used to increase the availability of suitable nest sites. Tern colonies are interconnected by dispersal, and a metapopulation approach is needed for effective management. Population dynamics are therefore affected by behaviors that influence the frequency of movement among colony sites： site fidelity, natal and breeding dispersal, and group adherence. The monogamous breeding system of terns should keep effective population size similar to census population size, but variation in sex ratios （likely resulting from sex differences in behavior） and in parental quality can result in a smaller than expected effective population size. In addition to the behavior of terns, knowledge of the behavior of predators on terns contributes to management plans, because predator behavior can sometimes be manipulated and predation is often performed by only a few specialized individuals. Other examples of links between tern behavior and conservation are also briefly reviewed, such as behavioral toxicology research and studies of behavioral responses to human disturbance and manmade structures. More work is needed on the behavior of migratory terns at staging sites, stopover sites and wintering grounds, and on the behavior of less well-studied species and species in less well-studied geographic regions [Current Zoology 60 （4）： 500-514, 2014].展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.12101443,12371493)the Natural Science Foundation of Shanxi Province(Grant Nos.20210302124260 and 202303021221024)。
文摘Livestock transportation is a key factor that contributes to the spatial spread of brucellosis.To analyze the impact of sheep transportation on brucellosis transmission,we develop a human–sheep coupled brucellosis model within a metapopulation network framework.Theoretically,we examine the positively invariant set,the basic reproduction number,the existence,uniqueness,and stability of disease-free equilibrium and the existence of the endemic equilibrium of the model.For practical application,using Heilongjiang province as a case study,we simulate brucellosis transmission across 12 cities based on data using three network types:the BA network,the ER network,and homogeneous mixing network.The simulation results indicate that the network's average degree plays a role in the spread of brucellosis.For BA and ER networks,the basic reproduction number and cumulative incidence of brucellosis stabilize when the network's average degree reaches 4 or 5.In contrast,sheep transport in a homogeneous mixing network accelerates the cross-regional spread of brucellosis,whereas transportation in a BA network helps to control it effectively.Furthermore,the findings suggest that the movement of sheep is not always detrimental to controlling the spread of brucellosis.For cities with smaller sheep populations,such as Shuangyashan and Qitaihe,increasing the transport of sheep outward amplifies the spatial spread of the disease.In contrast,in cities with larger sheep populations,such as Qiqihar,Daqing,and Suihua,moderate sheep outflow can help reduce the spread.In addition,cities with large livestock populations play a dominant role in the overall transmission dynamics,underscoring the need for stricter supervision in these areas.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11072107,91016022,and 11232007)the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures of Nanjing University of Aeronautics and astronautics,China(Grant No.0113G01)+1 种基金the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province,China(Grant No.13KJB110006)the Project Fund of Jiangsu University of Science and Technology,China(Grant No.633051203)
文摘We investigate the stochastic resonance （SR） phenomenon induced by the periodic signal in a metapopulation system with colored noises. The analytical expression of signal-to-noise is derived in the adiabatic limit. By numerical calculation, the effects of the addictive noise intensity, the multiplicative noise intensity and two noise self-correlation times on SNR are respectively discussed. It shows that： （i） in the case that the addictive noise intensity M takes a small value, a SR phenomenon for the curve of SNR appears; however, when M takes a large value, SNR turns into a monotonic function on the multiplicative noise intensity Q. （ii） The resonance peaks in the plots of the multiplicative noise intensity Q versus its self-correlation time Vl and the addictive noise intensity M versus its self-correlation time ~2 translate in parallel. Mean- while, a parallel translation also appears in the plots of vl versus Q and v2 versus M. （iii） The interactive effects between self-correlation times Vl and v2 are opposite.
文摘Hydrobiidae is one of the most diverse taxa among limnic and estuarine mollusks. Patterns of spatial and seasonal distribution of Heleobia australis were studied in ten stations over two years, in the urban eutrophic bay of Guanabara, Rio de Janeiro, Brazil. Spatial dispersal strategies in adults of this species, analyzed in the laboratory, revealed three patterns: 1) mobility on soft sediments;2) mobility on hard substrata;and 3) the ability to lift from the bottom to the surface, to again sink down. This facilitate species movement from one location to another by surface currents or attached to floating debris. Thus, individuals are able to escape from an impacted area and further re-colonize other patches after recovering from local impacts. The hypothesis of metapopulation dynamics (source– sink) was analyzed. Two stations with high and constant numbers of individuals were grouped and tested as possible ‘sources’. The number of specimens in the remaining stations was highly variable, even with the complete disappearance and posterior highly dense re-occurrence of the mollusk, whereby these were tested as possible ‘sinks’. Results derived from nested ANOVA supported the hypothesis of metapopulation dynamics in the case of H. australis adults, ex-pressed through opportunistic-species domi- nation of a highly impacted estuarine system, such as Guanabara Bay.
文摘The research on spatial epidemic models is a topic of considerable recent interest. In another hand, the advances in computer technology have stimulated the development of stochastic models. Metapopulation models are spatial designs that involve movements of individuals between distinct subpopulations. The purpose of the present work has been to develop stochastic models in order to study the transmission dynamics and control of infectious diseases in metapopulations. The authors studied Susceptible-Infected-Susceptible （SIS） and Susceptible-lnfected-Recovered （SIR） epidemic schemes, using the Gillespie algorithm, Computational numerical simulations were carried in order to explore the models. The results obtained show how the dynamics of transmission and the application of control measures within each subpopulation may affect all subpopulations of the system. They also show how the distribution of control measures among subpopulations affects the efficacy of these strategies. The dynamics of the stochastic models developed in the current study follow the trends observed in the classic deterministic designs. Also, the present models exhibit fluctuating behavior. This work highlights the importance of the spatial distribution of the population in spread and control of infectious diseases. In addition, it shows how chance could play an important role in these scenarios.
基金financially supported by Immunology Research Center,Tabriz University of Medical Sciences,Tabriz,Iran
文摘Objective: To verify phylogeography and genetic structure of Acanthamoeba populations among the Iranian clinical isolates and natural/artificial environments distributed in various regions of the country.Methods: We searched electronic databases including Medline, Pub Med, Science Direct, Scopus and Google Scholar from 2005 to 2016. To explore the genetic variability of Acanthamoeba sp, 205 sequences were retrieved from keratitis patients, immunosuppressed cases and environmental sources as of various geographies of Iran.Results: T4 genotype was the predominant strain in Iran, and the rare genotypes belonged to T2, T3, T5(Acanthamoeba lenticulata), T6, T9, T11, T13 and T15(Acanthamoeba jacobsi).A total of 47 unique haplotypes of T4 were identified. A parsimonious network of the sequence haplotypes demonstrated star-like feature containing haplogroups IR6(34.1%) and IR7(31.2%) as the most common haplotypes. In accordance with the analysis of molecular variance, the high value of haplotype diversity(0.612–0.848) of Acanthamoeba T4 represented genetic variability within populations. Neutrality indices of the 18 S ribosomal RNA demonstrated negative values in all populations which represented a considerable divergence from neutrality. The majority of genetic diversity belonged to the infected contact lens and dust samples in immunodeficiency and ophthalmology wards, which indicated potential routes for exposure to a pathogenic Acanthamoeba sp. in at-risk individuals. A pairwise fixation index(FST) was from low to high values(0.024 33–0.418 92). The statistically FST points out that T4 is genetically differentiated between north-west, north-south and centralsouth metapopulations, but not differentiated between west-central, west-south, centralsouth, and north-central isolates.Conclusions: An occurrence of IR6 and IR7 displays that possibly a gene flow of Acanthamoeba T4 occurred after the founder effect or bottleneck experience through ecological changes or host mobility. This is the first systematic review and meta-analysis providing new approaches into gene migration and transmission patterns of Acanthamoeba sp, and targeting at the high-risk individuals/sources among the various regions of Iran.
文摘The simplified incidence function model which is driven by the colored correlated noises is employed to investigate the extinction time of a metapopulation perturbed by environments. The approximate Fokker-Planck Equation and the mean first passage time which denotes the extinction time （Tex） are obtained by virtue of the Novikov theorem and the Fox approach. After introducing a noise intensity ratio and a dimensionless parameter R = D /α （D and a are the multiplicative and additive colored noise intensities respectively）, and then performing numerical computations, the results indicate that： （i） The absolute value of correlation strength A and its correlation time τ3 play opposite roles on the Tex; （ii） For the case of 0 〈λ〈 1,α and its correlation time τ2 play opposite roles on the Tex in which R〉 1 is the best condition, and there is one-peak structure on the Tex - D plot; （iii） For the case of-1 〈 λ≤ 0, D and its correlation time τ1 play opposite roles on the Tex in which R 〈 1 is the best condition and there is one-peak structure on the Tex - τ2 plot.
文摘We propose a metapopulation model with two geographical scales. In a regional scale, the model describes the dynamics of a collection of habitats connected by migratory movements. In a local scale, we consider some granularity within each habitat, in the sense that each habitat is itself a collection of patches linked by dispersal. The whole ensemble can be seen as a metapopulation composed by local metapopulations. We analyze the synchronization of the model in the two geographical scales. We present an analytic criterion for synchronization where only the habitats in the regional scale evolve with the same dynamics. Through numerical simulations, we discuss the different synchronization modes. It depends on how the individuals are distributed in the local patches that compose a habitat after migration takes place in the regional scale.
基金Nataša Djurdjevac Conrad and Johannes Zonker for discussions on the models initially developed in(Winkelmann et al.,2021)funding by the German Federal Ministry of Education and Research under grant agreement 031L0297B(Project INSIDe)+2 种基金funding by the German Federal Ministry for Digital and Transport under grant agreement FKZ19F2211A(Project PANDEMOS)funding by the German Federal Ministry for Digital and Transport under grant agreement FKZ19F2211B(Project PANDEMOS)funding from the Initiative and Networking Fund of the Helmholtz Association(grant agreement number KA1-Co-08,Project LOKI-Pandemics).
文摘Emerging infectious diseases and climate change are two of the major challenges in 21st century.Although over the past decades,highly-resolved mathematical models have contributed in understanding dynamics of infectious diseases and are of great aid when it comes to finding suitable intervention measures,they may need substantial computational effort and produce significant CO_(2) emissions.Two popular modeling approaches for mitigating infectious disease dynamics are agent-based and population-based models.Agent-based models(ABMs)offer a microscopic view and are thus able to capture heterogeneous human contact behavior and mobility patterns.However,insights on individual-level dynamics come with high computational effort that scales with the number of agents.On the other hand,population-based models(PBMs)using e.g.ordinary differential equations(ODEs)are computationally efficient even for large populations due to their complexity being independent of the population size.Yet,population-based models are restricted in their granularity as they assume a(to some extent)homogeneous and well-mixed population.To manage the trade-off between computational complexity and level of detail,we propose spatial-and temporal-hybrid models that use ABMs only in an area or time frame of interest.To account for relevant influences to disease dynamics,e.g.,from outside,due to commuting activities,we use population-based models,only adding moderate computational costs.Our hybridization approach demonstrates significant reduction in computational effort by up to 98%–without losing the required depth in information in the focus frame.The hybrid models used in our numerical simulations are based on two recently proposed models,however,any suitable combination of ABM and PBM could be used,too.Concluding,hybrid epidemiological models can provide insights on the individual scale where necessary,using aggregated models where possible,thereby making a contribution to green computing.
文摘The COVID-19 pandemic has had a tremendous impact on the transportation and tourism sectors.As vaccines were being administered and lockdowns implemented,owing to the significant social and economic impacts,travel bubbles were proposed as a gradual and intermediate open policy to balance risks and economic recovery.However,the travel bubble framework and associated costs and benefits were not well-established during policy implementation.In this study,we propose a travel bubble transportation framework using a metapopulation epidemic and mobility model,and conduct a cost-benefit analysis for the decision-making process during the border reopening phase.Our model focuses on the control of domestic and international long-distance travel inside the bubble to maximize monetary returns derived from tourism benefits and pandemic costs.A sequential decision problem is proposed to make multiple decisions based on real-time observations.We conduct a case study on travel bubbles in Australia,New Zealand,and Japan to test the feasibility of the model.The simulation results show that controlled intra-bubble transportation can generate positive economic benefits while keeping the epidemic within an acceptable range of control.Our framework can assist policymakers in making informed,open decisions by considering multiple attributes during a global pandemic.
基金This project was funded by the Pacific Southwest Regional Center of Excellence for Vector-borne Diseases funded by the US Centers for Disease Control and Prevention(Cooperative Agreement 1U01CK000649).
文摘Rocky Mountain spotted fever(RMSF)is a fatal tick-borne zoonotic disease that has emerged as an epidemic in western North America since the turn of the 21st century.Along the US south-western border and across northern Mexico,the brown dog tick,Rhipicephalus sanguineus,is responsible for spreading the disease between dogs and humans.The widespread nature of the disease and the ongoing epidemics contrast with historically sporadic patterns of the disease.Because dogs are amplifying hosts for the Rickettsia rickettsii bacteria,transmission dynamics between dogs and ticks are critical for understanding the epidemic.In this paper,we developed a compartment metapopulation model and used it to explore the dynamics and drivers of RMSF in dogs and brown dog ticks in a theoretical region in western North America.We discovered that there is an extended lag—as much as two years—between introduction of the pathogen to a naïve population and epidemic-level transmission,suggesting that infected ticks could disseminate extensively before disease is detected.A single large city-size population of dogs was sufficient to maintain the disease over a decade and serve as a source for disease in surrounding smaller towns.This model is a novel tool that can be used to identify high risk areas and key intervention points for epidemic RMSF spread by brown dog ticks.
基金One of the authors(ABG)acknowledge the support,in part,of the Simons Foundation(Award#585022)the National Science Foundation(Grant Number:DMS-2052363)Another author(SS)acknowledges the support of the Fulbright Scholarship.
文摘India has been the latest global epicenter for COVID-19,a novel coronavirus disease that emerged in China in late 2019.We present a base mathematical model for the transmission dynamics of COVID-19 in India and its neighbor,Pakistan.The base model was rigorously analyzed and parameterized using cumulative COVID-19 mortality data from each of the two countries.The model was used to assess the population-level impact of the control and mitigation strategies implemented in the two countries(notably non-pharmaceutical interventions).Numerical simulations of the basic model indicate that,based on the current baseline levels of the control and mitigation strategies implemented,the pandemic trajectory in India is on a downward trend.This downward trend will be reversed,and India will be recording mild outbreaks,if the control and mitigation strategies are relaxed from their current levels.By early September 2021,our simulations suggest that India could record up to 460,000 cumulative deaths under baseline levels of the implemented control strategies,while Pakistan(where the pandemic is comparatively milder)could see over 24,000 cumulative deaths at current mitigation levels.The basic model was extended to assess the impact of back-and-forth mobility between the two countries.Simulations of the resulting metapopulation model show that the burden of the COVID-19 pandemic in Pakistan increases with increasing values of the average time residents of India spend in Pakistan,with daily mortality in Pakistan peaking in mid-August to mid-September of 2021.Under the respective baseline control scenarios,our simulations show that the backand-forth mobility between India and Pakistan could delay the time-to-elimination of the COVID-19 pandemic in India and Pakistan to November 2022 and July 2022,respectively.
文摘According to investigation on two species of melitaeine butterflies in Yanjiaping Village, Chicheng County, Hebei Province, China, between 1998—2002, to-gether with the use of 1︰10000 contour map of the local area, some conclusions are shown by the SPSS and GIS analysis of data obained from GPS: (1) The two species of melitaeine butterflies have different metapopulation struc-tures. M. phoebe is a source-sink metapopulation, while E. aurinia is a classical metapopulation, supporting the analytic result from our former genetic research. (2) The two species of melitaeine butterflies exhibit different trends of popula-tion dynamics. M. phoebe source-sink metapopulation is very unsteady, and is always small, thus has a tendency to go ex-tinct gradually. But E. aurinia classical metapopulation is stable, and has maintained a larger population size. There-fore, it stands a better chance of long-term survival. (3) The two species of melitaeine butterflies are significantly related in both patch occupancy and local population size. (4) The effect of isolation is significant on the metapopulations of these two species of melitaeine butterflies, consistent with the classical theories, whereas the effect of patch area is not sig-nificant on the metapopulations of these two species of meli-taeine butterflies, which is inconsistent with the classical theories. Therefore, other factors, such as habitat quality, should be considered for their influences on metapopula-tions.
文摘This article discusses the influence of phenology-related intraseasonal asynchrony on metapopulation dynamics and stability. As the part played by intraseasonal asynchrony is as yet unclear and poorly described, greater account of it should be taken in both metapopulation research and conservation practice. The subpopulations of the Parnassius mnemosyne metapopulation studied here are strongly isolated because of the phenological shift between them, despite the relatively small physical distances between them. This isolation is the result of a significant temporal shift in the species' flight periods in the main metapopulation centers: in som e seasons its flight times in the different subpopulations did not overlap at all. The predicted results of such strong intraseasonal asynchrony are not altogether clear. On the one hand, they reduce the vulnerability of the entire metapopulation to the effects of short-term random disasters. On the other, the ever-greater isolation of subpopulations may cause the metapopulation to becom e a nonequilibrium one, which will have a serious impact on its long-term survival.
文摘The spread of methicillin-resistant strains of Staphylococcus aureus(MRSA)in health-care settings has become increasingly difficult to control and has since been able to spread in the general community.The prevalence of MRSA within the general public has caused outbreaks in groups of people in close quarters such as military barracks,gyms,daycare centres and correctional facilities.Correctional facilities are of particular importance for spreading MRSA,as inmates are often in close proximity and have limited access to hygienic products and clean clothing.Although these conditions are ideal for spreading MRSA,a recent study has suggested that recurrent epidemics are caused by the influx of colonized or infected individuals into the correctional facility.In this paper,we further investigate the effects of community dynamics on the spread of MRSA within the correctional facility and determine whether recidivism has a significant effect on disease dynamics.Using a simplified hotspot model ignoring disease dynamics within the correctional facility,as well as two metapopulation models,we demonstrate that outbreaks in correctional facilities can be driven by community dynamics even when spread between inmates is restricted.We also show that disease dynamics within the correctional facility and their effect on the outlying community may be ignored due to the smaller size of the incarcerated population.This will allow construction of simpler models that consider the effects of many MRSA hotspots interacting with the general community.It is suspected that the cumulative effects of hotspots for MRSA would have a stronger feedback effect in other community settings.
文摘Two stochastic models are derived for a susceptible-infectious-susceptible epidemic spreading through a metapopulation： a continuous time Markov chain （CTMC） model and an It6 stochastic differential equation （SDE） model. The stochastic models are numerically compared. Close agreement suggests that computationally intense CTMC simulations can be approximated by simpler SDE simulations. Differential equations for the moments of the SDE probability distribution are also derived, the steady states are solved numerically using a moment closure technique, and these results are compared to simulations. The moment closure technique only coarsely approximates simulation results. The effect of model parameters on stability of the disease-free equilibrium is also numerically investigated.
文摘Behavioral research has long had an important role in the conservation of terns （Ayes： Stemidae）. Habitat management and restoration of breeding colony sites depends on knowledge of the cues used to select colony and nest sites. For example, conspecific attraction with playback and decoys is commonly used to bring terns to suitable colony sites and habitat modification is often used to increase the availability of suitable nest sites. Tern colonies are interconnected by dispersal, and a metapopulation approach is needed for effective management. Population dynamics are therefore affected by behaviors that influence the frequency of movement among colony sites： site fidelity, natal and breeding dispersal, and group adherence. The monogamous breeding system of terns should keep effective population size similar to census population size, but variation in sex ratios （likely resulting from sex differences in behavior） and in parental quality can result in a smaller than expected effective population size. In addition to the behavior of terns, knowledge of the behavior of predators on terns contributes to management plans, because predator behavior can sometimes be manipulated and predation is often performed by only a few specialized individuals. Other examples of links between tern behavior and conservation are also briefly reviewed, such as behavioral toxicology research and studies of behavioral responses to human disturbance and manmade structures. More work is needed on the behavior of migratory terns at staging sites, stopover sites and wintering grounds, and on the behavior of less well-studied species and species in less well-studied geographic regions [Current Zoology 60 （4）： 500-514, 2014].
