Suzanne L. Robertson
Virginia Commonwealth University
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Featured researches published by Suzanne L. Robertson.
Journal of Theoretical Biology | 2013
Marisa C. Eisenberg; Suzanne L. Robertson; Joseph H. Tien
Cholera and many waterborne diseases exhibit multiple characteristic timescales or pathways of infection, which can be modeled as direct and indirect transmission. A major public health issue for waterborne diseases involves understanding the modes of transmission in order to improve control and prevention strategies. An important epidemiological question is: given data for an outbreak, can we determine the role and relative importance of direct vs. environmental/waterborne routes of transmission? We examine whether parameters for a differential equation model of waterborne disease transmission dynamics can be identified, both in the ideal setting of noise-free data (structural identifiability) and in the more realistic setting in the presence of noise (practical identifiability). We used a differential algebra approach together with several numerical approaches, with a particular emphasis on identifiability of the transmission rates. To examine these issues in a practical public health context, we apply the model to a recent cholera outbreak in Angola (2006). Our results show that the model parameters-including both water and person-to-person transmission routes-are globally structurally identifiable, although they become unidentifiable when the environmental transmission timescale is fast. Even for water dynamics within the identifiable range, when noisy data are considered, only a combination of the water transmission parameters can practically be estimated. This makes the waterborne transmission parameters difficult to estimate, leading to inaccurate estimates of important epidemiological parameters such as the basic reproduction number (R0). However, measurements of pathogen persistence time in environmental water sources or measurements of pathogen concentration in the water can improve model identifiability and allow for more accurate estimation of waterborne transmission pathway parameters as well as R0. Parameter estimates for the Angola outbreak suggest that both transmission pathways are needed to explain the observed cholera dynamics. These results highlight the importance of incorporating environmental data when examining waterborne disease.
Journal of Biological Dynamics | 2013
Suzanne L. Robertson; Marisa C. Eisenberg; Joseph H. Tien
Many factors influencing disease transmission vary throughout and across populations. For diseases spread through multiple transmission pathways, sources of variation may affect each transmission pathway differently. In this paper we consider a disease that can be spread via direct and indirect transmission, such as the waterborne disease cholera. Specifically, we consider a system of multiple patches with direct transmission occurring entirely within patch and indirect transmission via a single shared water source. We investigate the effect of heterogeneity in dual transmission pathways on the spread of the disease. We first present a 2-patch model for which we examine the effect of variation in each pathway separately and propose a measure of heterogeneity that incorporates both transmission mechanisms and is predictive of R0. We also explore how heterogeneity affects the final outbreak size and the efficacy of intervention measures. We conclude by extending several results to a more general n-patch setting.
Journal of Biological Dynamics | 2011
Suzanne L. Robertson; J. M. Cushing
Spatial segregation among life-cycle stages has been observed in many stage-structured species, including species of the flour beetle Tribolium. We investigate density-dependent dispersal of life-cycle stages as a possible mechanism responsible for this separation. We explore this hypothesis using stage-structured, integrodifference equation (IDE) models that incorporate density-dependent dispersal kernels. We first investigate mechanisms that can lead to spatial patterns in juvenile–adult IDE models. We show, via numerical simulation, that density-dependent dispersal can lead to the spatial segregation of life-cycle stages in the sense that each stage peaks in a different spatial location. We then construct a three-stage spatial model to describe the population dynamics of Tribolium castaneum and Tribolium confusum and assess density-dependent dispersal mechanisms that are able to explain spatial patterns that have been experimentally observed in these species.
Journal of Theoretical Biology | 2016
Suzanne L. Robertson; Kevin A. Caillouët
Though seasonal West Nile virus (WNV) outbreaks have been widely observed to be associated with the end of the avian nesting season, specific ecological mechanisms accounting for this synchronicity remain poorly understood. In this paper we develop and evaluate a novel mathematical model of enzootic WNV transmission to gain insight into the mechanisms responsible for structuring WNV dynamics. We incorporate avian (host) stage-structure (nestling, fledgling, and adult) and within-species heterogeneity in the form of stage-specific mosquito (vector) biting rates. We determine the extent to which temporal fluctuations in host stage and vector abundance throughout the season, along with the differential exposure of these stages to mosquito bites, affect the timing and magnitude of WNV outbreaks in the vector population. We find heterogeneity in avian stage exposure, particularly an increase in juvenile exposure, to result in earlier, more intense transmission. The effects of differential exposure are dependent upon vector abundance, both at carrying capacity as well as during initial stages of nestling production.
Siam Journal on Applied Dynamical Systems | 2003
Shandelle M. Henson; James R. Reilly; Suzanne L. Robertson; Matthew C. Schu; Eric William Davis Rozier; J. M. Cushing
Oscillating population data often exhibit cycle irregularities such as episodes of damped oscillation and abrupt changes of cycle phase. The prediction of such irregularities is of interest in applications ranging from food production to wildlife management. We use concepts from dynamical systems theory to present a model-based method for quantifying the risk of impending cycle irregularity.
Bellman Prize in Mathematical Biosciences | 2015
O.C. Collins; Suzanne L. Robertson; Keshlan S. Govinder
Waterborne diseases such as cholera continue to pose serious public health problems in the world today. Transmission parameters can vary greatly with socioeconomic class (SEC) and the availability of clean water. We formulate a multi-patch waterborne disease model such that each patch represents a particular SEC with its own water source, allowing individuals to move between SECs. For a 2-SEC model, we investigate the conditions under which each SEC is responsible for driving a cholera outbreak. We determine the effect of SECs on disease transmission dynamics by comparing the basic reproduction number of the 2-SEC model to that of a homogeneous model that does not take SECs into account. We conclude by extending several results of the 2-SEC model to an n-SEC model.
Letters in Biomathematics | 2017
Taylor A. Beebe; Suzanne L. Robertson
We develop a host–vector model of West Nile virus (WNV) transmission that incorporates multiple avian host species as well as host stage-structure (juvenile and adult stages), allowing for both species-specific and stage-specific biting rates of vectors on hosts. We use this ordinary differential equation model to explore WNV transmission dynamics that occur between vectors and multiple structured host populations as a result of heterogeneous biting rates on species and/or life stages. Our analysis shows that increased exposure of juvenile hosts generally results in larger outbreaks of WNV infectious vectors when compared to differential host species exposure. We also find that increased juvenile exposure is an important mechanism for determining the effect of species diversity on the disease risk of a community.
Archive | 2017
Arietta Fleming-Davies; Sara Jabbari; Suzanne L. Robertson; Tri Sri Noor Asih; Cristina Lanzas; Suzanne Lenhart; Casey M. Theriot
Clostridium difficile is the leading cause of infectious diarrhea in hospitals and one of the most common healthcare associated infections. Antibiotics alter the normal gut microbiota and facilitate the colonization of enteric pathogens such as C. difficile. Our objective is to elucidate the role of bile acids and other mechanisms in providing colonization resistance against C. difficile. We formulated and analyzed differential equation models for microbial interactions in the gut and bile acid dynamics, as well as a combined model including both mechanisms. Our analysis indicates that bile acids do not prevent C. difficile colonization, but they regulate the onset of C. difficile colonization and growth after antibiotic perturbation. These results have implications in the development of novel ways to inhibit C. difficile infection.
Methods of Molecular Biology | 2016
Kevin A. Caillouët; Suzanne L. Robertson
Interpretation of enzootic West Nile virus (WNV) surveillance indicators requires little advanced mathematical skill, but greatly enhances the ability of public health officials to prescribe effective WNV management tactics. Stepwise procedures for the calculation of mosquito infection rates (IR) and vector index (VI) are presented alongside statistical tools that require additional computation. A brief review of advantages and important considerations for each statistics use is provided.
Bulletin of Mathematical Biology | 2012
Suzanne L. Robertson; J. M. Cushing; Robert F. Costantino
In many stage-structured species, different life stages often occupy separate spatial niches in a heterogeneous environment. Life stages of the giant flour beetle Tribolium brevicornis (Leconte), in particular adults and pupae, occupy different locations in a homogeneous habitat. This unique spatial pattern does not occur in the well-studied stored grain pests T. castaneum (Herbst) and T. confusum (Duval). We propose density dependent dispersal as a causal mechanism for this spatial pattern. We model and explore the spatial dynamics of T. brevicornis with a set of four density dependent integrodifference and difference equations. The spatial model exhibits multiple attractors: a spatially uniform attractor and a patchy attractor with pupae and adults spatially separated. The model attractors are consistent with experimental observations.