22 results found
Erguler K, Chandra NL, Proestos Y, et al., 2017, A large-scale stochastic spatiotemporal model for Aedes albopictus-borne chikungunya epidemiology, PLOS ONE, Vol: 12, ISSN: 1932-6203
Erguler K, Smith-Unna SE, Waldock J, et al., 2016, Large-Scale Modelling of the Environmentally-Driven Population Dynamics of Temperate Aedes albopictus (Skuse), PLOS One, Vol: 11, ISSN: 1932-6203
The Asian tiger mosquito, Aedes albopictus, is a highly invasive vector species. It is a proven vector of dengue and chikungunya viruses, with the potential to host a further 24 arboviruses. It has recently expanded its geographical range, threatening many countries in the Middle East, Mediterranean, Europe and North America. Here, we investigate the theoretical limitations of its range expansion by developing an environmentally-driven mathematical model of its population dynamics. We focus on the temperate strain of Ae. albopictus and compile a comprehensive literature-based database of physiological parameters. As a novel approach, we link its population dynamics to globally-available environmental datasets by performing inference on all parameters. We adopt a Bayesian approach using experimental data as prior knowledge and the surveillance dataset of Emilia-Romagna, Italy, as evidence. The model accounts for temperature, precipitation, human population density and photoperiod as the main environmental drivers, and, in addition, incorporates the mechanism of diapause and a simple breeding site model. The model demonstrates high predictive skill over the reference region and beyond, confirming most of the current reports of vector presence in Europe. One of the main hypotheses derived from the model is the survival of Ae. albopictus populations through harsh winter conditions. The model, constrained by the environmental datasets, requires that either diapausing eggs or adult vectors have increased cold resistance. The model also suggests that temperature and photoperiod control diapause initiation and termination differentially. We demonstrate that it is possible to account for unobserved properties and constraints, such as differences between laboratory and field conditions, to derive reliable inferences on the environmental dependence of Ae. albopictus populations.
Christiansen-Jucht C, Parham PE, Saddler A, et al., 2015, Larval and adult environmental temperatures influence the adult reproductive traits of Anopheles gambiae s.s., Parasites & Vectors, Vol: 8, ISSN: 1756-3305
BackgroundAnopheles mosquito life-history parameters and population dynamics strongly influence malaria transmission, and environmental factors, particularly temperature, strongly affect these parameters. There are currently some studies on how temperature affects Anopheles gambiae s.s. survival but very few exist examining other life-history traits. We investigate here the effect of temperature on population dynamics parameters.MethodsAnopheles gambiae s.s. immatures were reared individually at 23 ± 1 °C, 27 ± 1 °C, 31 ± 1 °C, and 35 ± 1 °C, and adults were held at their larval temperature or at one of the other temperatures. Larvae were checked every 24 h for development to the next stage and measured for size; wing length was measured as a proxy for adult size. Females were blood fed three times, and the number of females feeding and laying eggs was counted. The numbers of eggs and percentage of eggs hatched were recorded.ResultsIncreasing temperatures during the larval stages resulted in significantly smaller larvae (p = 0.005) and smaller adults (p < 0.001). Adult temperature had no effect on the time to egg laying, and the larval temperature of adults only affected the incubation period of the first egg batch. Temperature influenced the time to hatching of eggs, as well as the time to development at every stage. The number of eggs laid was highest when adults were kept at 27 °C, and lowest at 31 °C, and higher adult temperatures decreased the proportion of eggs hatching after the second and third blood meal. Higher adult temperatures significantly decreased the probability of blood feeding, but the larval temperature of adults had no influence on the probability of taking a blood meal. Differences were observed between the first, second, and third blood meal in the times to egg laying and hatching, number of eggs laid, and
Christiansen-Jucht C, Erguler K, Shek CY, et al., 2015, Modelling Anopheles gambiae s.s. Population Dynamics with Temperature- and Age-Dependent Survival, International Journal of Environmental Research and Public Health, Vol: 12, Pages: 5975-6005, ISSN: 1660-4601
Climate change and global warming are emerging as important threats to humanhealth, particularly through the potential increase in vector- and water-borne diseases.Environmental variables are known to affect substantially the population dynamics andabundance of the poikilothermic vectors of disease, but the exact extent of this sensitivity isnot well established. Focusing on malaria and its main vector in Africa, Anopheles gambiaesensu stricto, we present a set of novel mathematical models of climate-driven mosquitopopulation dynamics motivated by experimental data suggesting that in An. gambiae,mortality is temperature and age dependent. We compared the performance of these modelsto that of a ―standard‖ model ignoring age dependence. We used a longitudinal dataset ofvector abundance over 36 months in sub-Saharan Africa for comparison between modelsthat incorporate age dependence and one that does not, and observe that age-dependentmodels consistently fitted the data better than the reference model. This highlights thatincluding age dependence in the vector component of mosquito-borne disease models maybe important to predict more reliably disease transmission dynamics. Further data and studies are needed to enable improved fitting, leading to more accurate and informativemodel predictions for the An. gambiae malaria vector as well as for other disease vectors.
Parham PE, Waldock J, Christophides GK, et al., 2015, Climate, environmental and socio-economic change: weighing up the balance in vector-borne disease transmission, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 370, ISSN: 0962-8436
Medone P, Ceccarelli S, Parham PE, et al., 2015, The impact of climate change on the geographical distribution of two vectors of Chagas disease: implications for the force of infection, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 370, ISSN: 0962-8436
Parham PE, Hughes DA, 2015, Climate influences on the cost-effectiveness of vector-based interventions against malaria in elimination scenarios, Philosophical Transactions of the Royal Society B: Biological Sciences, Vol: 370, Pages: 20130557-20130557, ISSN: 0962-8436
<jats:p> Despite the dependence of mosquito population dynamics on environmental conditions, the associated impact of climate and climate change on present and future malaria remains an area of ongoing debate and uncertainty. Here, we develop a novel integration of mosquito, transmission and economic modelling to assess whether the cost-effectiveness of indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) against <jats:italic>Plasmodium falciparum</jats:italic> transmission by <jats:italic>Anopheles gambiae</jats:italic> s.s. mosquitoes depends on climatic conditions in low endemicity scenarios. We find that although temperature and rainfall affect the cost-effectiveness of IRS and/or LLIN scale-up, whether this is sufficient to influence policy depends on local endemicity, existing interventions, host immune response to infection and the emergence rate of insecticide resistance. For the scenarios considered, IRS is found to be more cost-effective than LLINs for the same level of scale-up, and both are more cost-effective at lower mean precipitation and higher variability in precipitation and temperature. We also find that the dependence of peak transmission on mean temperature translates into optimal temperatures for vector-based intervention cost-effectiveness. Further cost-effectiveness analysis that accounts for country-specific epidemiological and environmental heterogeneities is required to assess optimal intervention scale-up for elimination and better understand future transmission trends under climate change. </jats:p>
Parham PE, Waldock J, Christophides GK, et al., 2015, Climate change and vector-borne diseases of humans Preface, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 370, ISSN: 0962-8436
Christiansen-Jucht C, Parham PE, Saddler A, et al., 2014, Temperature during larval development and adult maintenance influences the survival of Anopheles gambiae s.s., PARASITES & VECTORS, Vol: 7, ISSN: 1756-3305
Waldock J, Parham PE, Lelieveld J, et al., 2013, Climate and Human Health: The Impact of Climate Change on Vector-Borne Diseases, Paphos, Cyprus (17-19 October 2012), PATHOGENS AND GLOBAL HEALTH, Vol: 107, Pages: 387-392, ISSN: 2047-7724
Waldock J, Chandra NL, Lelieveld J, et al., 2013, The role of environmental variables on Aedes albopictus biology and chikungunya epidemiology, PATHOGENS AND GLOBAL HEALTH, Vol: 107, Pages: 224-241, ISSN: 2047-7724
Slater HC, Gambhir M, Parham PE, et al., 2013, Modelling Co-Infection with Malaria and Lymphatic Filariasis, PLoS Comput Biol, Vol: 9
<title>Author Summary</title><p>Malaria and lymphatic filariasis (LF) are thought to be co-endemic in many regions of Africa. Currently, most interventions targeted at these infections do not consider the impacts of co-infection. However, there have been increasing calls to adopt integrated control programmes that can achieve synergistic effects. Malaria and LF are both vector-borne diseases transmitted by <italic>Anopheles</italic> spp. mosquitoes, suggesting that well-designed vector control strategies have the potential to affect the transmission of both infections. In this study, we develop a modelling framework incorporating the specifics of malaria-LF co-infection to investigate how the transmission of each infection is altered for a range of possible interaction scenarios. We find that a control strategy that reduces LF transmission (via mass drug administration, for example) could potentially increase malaria prevalence. This work illustrates the potential perverse effects of targeting just one infection and emphasises the need to take into account co-endemic diseases when designing control programmes. The developed modelling framework can provide the basis for exploring the mix of options for joint control of these infections. We also highlight the need for better data on how co-infection impacts hosts and vectors in order for future predictions on both co-transmission dynamics and control to become more reliable.</p>
Waldock J, Chandra NL, Lelieveld J, et al., 2012, The Role of Environmental Variables on Aedes albopictus Biology and Distribution and the Epidemiology of Chikungunya Infection, Pathogens and Global Health
Gambhir M, Parham PE, White PJ, 2012, Using Infectious Disease Models to Inform Public Health Policies: Construction, Analysis, and Evaluation, BMJ
Parham PE, Pople D, Christiansen-Jucht C, et al., 2012, Modelling the Role of Environmental Variables on the Population Dynamics of the Malaria Vector Anopheles gambiae sensu stricto, Malaria Journal, Vol: 11: 271
Parham PE, Christiansen-Jucht C, Pople D, et al., 2011, Understanding and Modelling the Impact of Climate Change on Infectious Diseases – Progress and Future Challenges, Climate Change - Socioeconomic Effects, Editors: Blanco, Kheradmand, Publisher: InTech, Pages: 43-66, ISBN: 978-953-307-411-5
Singh BK, Parham PE, Hu CK, 2011, Structural Perturbations to Population Skeletons:Transient Dynamics, Coexistence of Attractors and the Rarity of Chaos, PLoS ONE, Vol: 6(9): e24200
Parham PE, Michael E, 2011, Outbreak Properties of Epidemic Models: The Roles of Temporal Forcing and Stochasticity on Pathogen Invasion Dynamics, J THEOR BIOL, Vol: 271, Pages: 1-9
Parham PE, Michael E, 2010, Modelling the Effects of Weather and Climate Change on Malaria Transmission, Environ Health Perspect
Parham PE, Michael E, 2010, Modelling Climate Change and Malaria Transmission, Advances in Experimental Medicine and Biology, Vol: 673, Pages: 184-199, ISSN: 0065-2598
Parham PE, Singh BK, Ferguson NM, 2008, Analytic Approximation of Spatial Epidemic Models of Foot and Mouth Disease, THEOR POPUL BIOL, Vol: 73, Pages: 349-368, ISSN: 0040-5809
The effect of spatial heterogeneity in epidemic models has improved with computational advances, yet far less progress has been made in developing analytical tools for understanding such systems. Here, we develop two classes of second-order moment closure methods for approximating the dynamics of a stochastic spatial model of the spread of foot and mouth disease. We consider the performance of such 'pseudo-spatial' models as a function of R-0, the locality in disease transmission, farm distribution and geographically-targeted control when an arbitrary number of spatial kernels are incorporated. One advantage of mapping complex spatial models onto simpler deterministic approximations lies in the ability to potentially obtain a better analytical understanding of disease dynamics and the effects of control. We exploit this tractability by deriving analytical results in the invasion stages of an FMD outbreak, highlighting key principles underlying epidemic spread on contact networks and the effect of spatial correlations. (C) 2008 Elsevier Inc. All rights reserved.
Parham PE, Ferguson NM, 2006, Space and Contact Networks: Capturing the Locality of Disease Transmission, J R SOC INTERFACE, Vol: 3, Pages: 483-493, ISSN: 1742-5689
While an arbitrary level of complexity may be included in simulations of spatial epidemics, computational intensity and analytical intractability mean that such models often lack transparency into the determinants of epidemiological dynamics. Although numerous approaches attempt to resolve this complexity tractability trade-off,moment closure methods arguably offer the most promising and robust frameworks for capturing the role of the locality of contact processes on global disease dynamics. While a close analogy may be made between full stochastic spatial transmission models and dynamic network models, we consider here the special case where the dynamics of the network topology change on time-scales much longer than the epidemiological processes imposed on them; in such cases, the use of static network models are justified. We show that in such cases, static network models may provide excellent approximations to the underlying spatial contact process through an appropriate choice of the effective neighbourhood size. We also demonstrate the robustness of this mapping by examining the equivalence of deterministic approximations to the full spatial and network models derived under third-order moment closure assumptions. For systems where deviation from homogeneous mixing is limited, we show that pair equations developed for network models are at least as good an approximation to the underlying stochastic spatial model as more complex spatial moment equations, with both classes of approximation becoming less accurate only for highly localized kernels.
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