Publications by authors named "Sadie J Ryan"

89 Publications

The future of zoonotic risk prediction.

Philos Trans R Soc Lond B Biol Sci 2021 11 20;376(1837):20200358. Epub 2021 Sep 20.

Center for Global Health Science and Security, Georgetown University Medical Center, Washington, DC 20007, USA.

In the light of the urgency raised by the COVID-19 pandemic, global investment in wildlife virology is likely to increase, and new surveillance programmes will identify hundreds of novel viruses that might someday pose a threat to humans. To support the extensive task of laboratory characterization, scientists may increasingly rely on data-driven rubrics or machine learning models that learn from known zoonoses to identify which animal pathogens could someday pose a threat to global health. We synthesize the findings of an interdisciplinary workshop on zoonotic risk technologies to answer the following questions. What are the prerequisites, in terms of open data, equity and interdisciplinary collaboration, to the development and application of those tools? What effect could the technology have on global health? Who would control that technology, who would have access to it and who would benefit from it? Would it improve pandemic prevention? Could it create new challenges? This article is part of the theme issue 'Infectious disease macroecology: parasite diversity and dynamics across the globe'.
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http://dx.doi.org/10.1098/rstb.2020.0358DOI Listing
November 2021

Sex-Specific Elk Resource Selection during the Anthrax Risk Period.

J Wildl Manage 2021 Jan 1;85(1):145-155. Epub 2020 Oct 1.

Spatial Epidemiology and Ecology Research Laboratory, Department of Geography, Emerging Pathogens Institute, University of Florida, Gainesville, FL 32611, USA.

Anthrax, caused by the spore-forming bacterium , is a zoonosis affecting animals and humans globally. In the United States, anthrax outbreaks occur in wildlife and livestock, with frequent outbreaks in native and exotic wildlife species in Texas, livestock outbreaks in the Dakotas, and sporadic mixed outbreaks in Montana. Understanding where pathogen and host habitat selection overlap is essential for anthrax management. Resource selection and habitat use of ungulates may be sex-specific and lead to differential anthrax exposure risks across the landscape for males and females. We evaluated female elk () resource selection in the same study areas as male elk in a previous anthrax risk study to identify risk of anthrax transmission to females and compare transmission risk between females and males. We developed a generalized linear mixed-effect model to estimate resource selection for female elk in southwest Montana during the June to August anthrax transmission risk period. We then predicted habitat selection of female and male elk across the study area and compared selection with the distribution of anthrax risk to identify spatial distributions of potential anthrax exposure for the male and female elk. Female and male elk selected different resources during the anthrax risk period, which resulted in different anthrax exposure areas for females and males. The sex-specific resource selection and habitat use could infer different areas of risk for anthrax transmission, which can improve anthrax and wildlife management and have important public health and economic implications.
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http://dx.doi.org/10.1002/jwmg.21952DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8356676PMC
January 2021

Predicting temperature-dependent transmission suitability of bluetongue virus in livestock.

Parasit Vectors 2021 Jul 30;14(1):382. Epub 2021 Jul 30.

Department of Biological Sciences, Virginia Tech, Blacksburg, VA, 24061, USA.

The transmission of vector-borne diseases is governed by complex factors including pathogen characteristics, vector-host interactions, and environmental conditions. Temperature is a major driver for many vector-borne diseases including Bluetongue viral (BTV) disease, a midge-borne febrile disease of ruminants, notably livestock, whose etiology ranges from mild or asymptomatic to rapidly fatal, thus threatening animal agriculture and the economy of affected countries. Using modeling tools, we seek to predict where the transmission can occur based on suitable temperatures for BTV. We fit thermal performance curves to temperature-sensitive midge life-history traits, using a Bayesian approach. We incorporate these curves into S(T), a transmission suitability metric derived from the disease's basic reproductive number, [Formula: see text] This suitability metric encompasses all components that are known to be temperature-dependent. We use trait responses for two species of key midge vectors, Culicoides sonorensis and Culicoides variipennis present in North America. Our results show that outbreaks of BTV are more likely between 15[Formula: see text] C and [Formula: see text], with predicted peak transmission risk at 26 [Formula: see text] C. The greatest uncertainty in S(T) is associated with the following: the uncertainty in mortality and fecundity of midges near optimal temperature for transmission; midges' probability of becoming infectious post-infection at the lower edge of the thermal range; and the biting rate together with vector competence at the higher edge of the thermal range. We compare three model formulations and show that incorporating thermal curves into all three leads to similar BTV risk predictions. To demonstrate the utility of this modeling approach, we created global suitability maps indicating the areas at high and long-term risk of BTV transmission, to assess risk and to anticipate potential locations of disease establishment.
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http://dx.doi.org/10.1186/s13071-021-04826-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8323090PMC
July 2021

HIV-Related Stigma Moderates the Relation Between Perceived Susceptibility and HIV Testing Intention Among Heterosexual (but Not Sexual Minority) College Students.

Health Promot Pract 2021 Jul 7:15248399211024993. Epub 2021 Jul 7.

University of Florida, Gainesville, FL, USA.

HIV-related stigma remains a considerable barrier to engaging at-risk populations in HIV testing and prevention programs. We assessed the moderating role of HIV-related stigma on the relation between perceived susceptibility to HIV and HIV testing intention among college students. We hypothesized that the moderating role of HIV-related stigma would be differential between heterosexual and sexual minority college students. We administered a survey focused on HIV-related knowledge, attitudes, and behaviors in spring 2016 ( = 2,159). We used multigroup path analysis to analyze the hypothesized moderation. HIV-related stigma moderated the relation between perceived susceptibility and testing intention for heterosexual but not sexual minority college students. Specifically, higher HIV-related stigma decreased the association between perceived susceptibility and testing intention. These results demonstrate the importance of priority population segmentation for HIV testing campaigns.
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http://dx.doi.org/10.1177/15248399211024993DOI Listing
July 2021

Anthrax Surveillance and the Limited Overlap Between Obligate Scavengers and Endemic Anthrax Zones in the United States.

Vector Borne Zoonotic Dis 2021 Sep 1;21(9):675-684. Epub 2021 Jun 1.

Spatial Epidemiology and Ecology Research Laboratory, Department of Geography, University of Florida, Gainesville, Florida, USA.

Anthrax is a zoonosis caused by the spore-forming bacterium , with potential for high fatality rate, especially in herbivores. Upon host death, spores can enter the soil surrounding the carcass and be ingested by other animals feeding in the same location. Accordingly, surveillance to quickly identify and decontaminate anthrax carcasses is crucial to outbreak prevention. In endemic anthrax areas such as Texas and Africa, vultures are used as a surveillance tool for identifying presence and location of dead animals. However, many anthrax outbreaks in the United States have occurred in areas outside the ranges of both black and turkey vultures. Here, we used a longitudinal camera trap survey at carcass sites in southwestern Montana to investigate the utility of facultative avian scavengers on disease and carcass surveillance in a reemerging anthrax risk zone. From August 2016 to September 2018, camera traps at 11 carcass sites were triggered 1996 times by avian scavengers. While the majority were facultative avian scavengers such as corvids and eagles, our results suggest that facultative scavengers cannot replace vultures as a surveillance tool in this ecosystem due to their absence during the anthrax risk period (June to August), reduced search efficiency, or low flight patterns. We found that the conditions in Montana likely parallel systems elsewhere in the continental United States. Using ecological niche models of distribution overlaid with relative abundance maps of turkey vultures, we found that much of North Dakota, South Dakota, Minnesota, Wyoming, Nebraska, and Iowa have areas of anthrax risk, but low or absent turkey vulture populations. Without vultures in these areas, surveillance capacity is reduced, and it becomes more difficult to identify anthrax cases, meaning fewer carcasses are decontaminated, and consequently, outbreaks could become more frequent or severe.
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http://dx.doi.org/10.1089/vbz.2020.2747DOI Listing
September 2021

Trends and Opportunities in Tick-Borne Disease Geography.

J Med Entomol 2021 May 24. Epub 2021 May 24.

Center for Global Health Science and Security, Georgetown University Medical Center, Georgetown University, Washington, DC, USA.

Tick-borne diseases are a growing problem in many parts of the world, and their surveillance and control touch on challenging issues in medical entomology, agricultural health, veterinary medicine, and biosecurity. Spatial approaches can be used to synthesize the data generated by integrative One Health surveillance systems, and help stakeholders, managers, and medical geographers understand the current and future distribution of risk. Here, we performed a systematic review of over 8,000 studies and identified a total of 303 scientific publications that map tick-borne diseases using data on vectors, pathogens, and hosts (including wildlife, livestock, and human cases). We find that the field is growing rapidly, with the major Ixodes-borne diseases (Lyme disease and tick-borne encephalitis in particular) giving way to monitoring efforts that encompass a broader range of threats. We find a tremendous diversity of methods used to map tick-borne disease, but also find major gaps: data on the enzootic cycle of tick-borne pathogens is severely underutilized, and mapping efforts are mostly limited to Europe and North America. We suggest that future work can readily apply available methods to track the distributions of tick-borne diseases in Africa and Asia, following a One Health approach that combines medical and veterinary surveillance for maximum impact.
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http://dx.doi.org/10.1093/jme/tjab086DOI Listing
May 2021

Effects of changes in temperature on Zika dynamics and control.

J R Soc Interface 2021 05 5;18(178):20210165. Epub 2021 May 5.

Department of Global Health and Social Medicine, Harvard Medical School, Boston, MA 02115, USA.

When a rare pathogen emerges to cause a pandemic, it is critical to understand its dynamics and the impact of mitigation measures. We use experimental data to parametrize a temperature-dependent model of Zika virus (ZIKV) transmission dynamics and analyse the effects of temperature variability and control-related parameters on the basic reproduction number () and the final epidemic size of ZIKV. Sensitivity analyses show that these two metrics are largely driven by different parameters, with the exception of temperature, which is the dominant driver of epidemic dynamics in the models. Our estimate has a single optimum temperature (≈30°C), comparable to other published results (≈29°C). However, the final epidemic size is maximized across a wider temperature range, from 24 to 36°C. The models indicate that ZIKV is highly sensitive to seasonal temperature variation. For example, although the model predicts that ZIKV transmission cannot occur at a constant temperature below 23°C (≈ average annual temperature of Rio de Janeiro, Brazil), the model predicts substantial epidemics for areas with a mean temperature of 20°C if there is seasonal variation of 10°C (≈ average annual temperature of Tampa, Florida). This suggests that the geographical range of ZIKV is wider than indicated from static models, underscoring the importance of climate dynamics and variation in the context of broader climate change on emerging infectious diseases.
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http://dx.doi.org/10.1098/rsif.2021.0165DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8097513PMC
May 2021

Are malaria transmission-blocking vaccines acceptable to high burden communities? Results from a mixed methods study in Bo, Sierra Leone.

Malar J 2021 Apr 13;20(1):183. Epub 2021 Apr 13.

CDC Southeastern Center of Excellence in Vector Borne Diseases, Gainesville, FL, USA.

Background: Malaria transmission-blocking vaccines (TBVs) could help break the cycle of malaria transmission by conferring community rather than individual protection. When introducing new intervention strategies, uptake is dependent on acceptability, not just efficacy. In this exploratory study on acceptability of TBVs in Sierra Leone, it was hypothesized that TBVs would be largely acceptable to adults and health workers in areas with relatively few ongoing malaria interventions, and that (i) knowledge of malaria and vaccines, (ii) health behaviours associated with malaria and vaccines, and (iii) attitudes towards different vaccines types could lead to greater TBV acceptability.

Methods: This study used a mixed methods approach in Bo, Sierra Leone, to understand community knowledge, attitudes, and practices related to malaria and vaccination in general. This included: (i) a population-based cross-sectional survey (n=615 adults), (ii) 6 focus group discussions with parents, and (iii) 20 key informant interviews. The concept of a TBV was explained to participants before they were asked about their willingness to accept this vaccine modality as part of an integrated malaria elimination programme.

Results: This study found that most adults would be willing to receive a TBV vaccine. Respondents noted mostly positive past experiences with adult and childhood vaccinations for other infectious diseases and high levels of engagement in other malaria prevention behaviors such as bed nets. Perceived barriers to TBV acceptance were largely focused on general community-level distribution of a vaccine, including personal fears of vaccination and possible costs. After an explanation of the TBV mechanism, nearly all focus group and interview participants believed that community members would accept the vaccine as part of an integrated malaria control approach. Both parents and health workers offered insight on how to successfully roll-out a future TBV vaccination programme.

Conclusions: The willingness of community members in Bo, Sierra Leone to accept a TBV as part of an integrated anti-malarial strategy suggests that the atypical mechanism of TBV action might not be an obstacle to future clinical trials. This study's findings suggests that perceived general barriers to vaccination implementation, such as perceived personal fears and vaccine cost, must be addressed in future clinical and implementation research studies.
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http://dx.doi.org/10.1186/s12936-021-03723-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8045381PMC
April 2021

Exploring the utility of social-ecological and entomological risk factors for dengue infection as surveillance indicators in the dengue hyper-endemic city of Machala, Ecuador.

PLoS Negl Trop Dis 2021 03 19;15(3):e0009257. Epub 2021 Mar 19.

Quantitative Disease Ecology and Conservation (QDEC) Lab Group, Department of Geography, University of Florida, Gainesville, Florida, United States of America.

The management of mosquito-borne diseases is a challenge in southern coastal Ecuador, where dengue is hyper-endemic and co-circulates with other arboviral diseases. Prior work in the region has explored social-ecological factors, dengue case data, and entomological indices. In this study, we bring together entomological and epidemiological data to describe links between social-ecological factors associated with risk of dengue transmission at the household level in Machala, Ecuador. Households surveys were conducted from 2014-2017 to assess the presence of adult Aedes aegypti (collected via aspiration) and to enumerate housing conditions, demographics, and mosquito prevention behaviors. Household-level dengue infection status was determined by laboratory diagnostics in 2014-2015. Bivariate analyses and multivariate logistic regression models were used to identify social-ecological variables associated with household presence of female Ae. aegypti and household dengue infection status, respectively. Aedes aegypti presence was associated with interruptions in water service and weekly trash collection, and household air conditioning was protective against mosquito presence. Presence of female Ae. aegypti was not associated with household dengue infections. We identified shaded patios and head of household employment status as risk factors for household-level dengue infection, while window screening in good condition was identified as protective against dengue infection. These findings add to our understanding of the systems of mosquito-borne disease transmission in Machala, and in the larger region of southern Ecuador, aiding in the development of improved vector surveillance efforts, and targeted interventions.
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http://dx.doi.org/10.1371/journal.pntd.0009257DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8011822PMC
March 2021

Scoping review of distribution models for selected ticks and rickettsial group pathogens.

PeerJ 2021 17;9:e10596. Epub 2021 Feb 17.

Department of Geography, University of Florida, Gainesville, FL, USA.

The rising prevalence of tick-borne diseases in humans in recent decades has called attention to the need for more information on geographic risk for public health planning. Species distribution models (SDMs) are an increasingly utilized method of constructing potential geographic ranges. There are many knowledge gaps in our understanding of risk of exposure to tick-borne pathogens, particularly for those in the rickettsial group. Here, we conducted a systematic scoping review of the SDM literature for rickettsial pathogens and tick vectors in the genus . Of the 174 reviewed articles, only 24 studies used SDMs to estimate the potential extent of vector and/or pathogen ranges. The majority of studies (79%) estimated only tick distributions using vector presence as a proxy for pathogen exposure. Studies were conducted at different scales and across multiple continents. Few studies undertook original data collection, and SDMs were mostly built with presence-only datasets from public database or surveillance sources. The reliance on existing data sources, using ticks as a proxy for disease risk, may simply reflect a lag in new data acquisition and a thorough understanding of the tick-pathogen ecology involved.
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http://dx.doi.org/10.7717/peerj.10596DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7896504PMC
February 2021

Climate predicts geographic and temporal variation in mosquito-borne disease dynamics on two continents.

Nat Commun 2021 02 23;12(1):1233. Epub 2021 Feb 23.

Department of Biology, Stanford University, Stanford, CA, USA.

Climate drives population dynamics through multiple mechanisms, which can lead to seemingly context-dependent effects of climate on natural populations. For climate-sensitive diseases, such as dengue, chikungunya, and Zika, climate appears to have opposing effects in different contexts. Here we show that a model, parameterized with laboratory measured climate-driven mosquito physiology, captures three key epidemic characteristics across ecologically and culturally distinct settings in Ecuador and Kenya: the number, timing, and duration of outbreaks. The model generates a range of disease dynamics consistent with observed Aedes aegypti abundances and laboratory-confirmed arboviral incidence with variable accuracy (28-85% for vectors, 44-88% for incidence). The model predicted vector dynamics better in sites with a smaller proportion of young children in the population, lower mean temperature, and homes with piped water and made of cement. Models with limited calibration that robustly capture climate-virus relationships can help guide intervention efforts and climate change disease projections.
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http://dx.doi.org/10.1038/s41467-021-21496-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7902664PMC
February 2021

Factors influencing scavenger guilds and scavenging efficiency in Southwestern Montana.

Sci Rep 2021 Feb 19;11(1):4254. Epub 2021 Feb 19.

Spatial Epidemiology & Ecology Research Laboratory, Department of Geography, University of Florida, Gainesville, FL, USA.

Scavenging of carrion shapes ecological landscapes by influencing scavenger population demography, increasing inter- and intra-specific interactions, and generating ecosystem services such as nutrient cycling and disease moderation. Previous research found the cues promoting, or the constraints limiting, an individual's propensity or ability to scavenge vary widely, depending on anthropogenic and environmental factors. Here we investigated differences in scavenging patterns in a complex scavenger guild in Southwestern Montana. We used camera traps established at 13 carcass sites to monitor carcass detection, visitation, and consumption times, during 2016-2018 and generalized linear models to explore the influence of carcass characteristics, habitat features, and seasonality, on carcass selection and scavenging efficiency. We found that scavenger species diversity was higher at higher elevations and in grassland habitats. Scavenging efficiency was influenced inter alia by seasonality, distance to water, and elevation. We found that most carcass consumption was via facultative scavengers (bears, wolves, magpies, Corvus spp.) rather than turkey vultures, the only obligate scavengers in the study area. However, growing populations of turkey vultures may lead to increased competition with facultative scavengers over carrion, and could have cascading effects on food webs in this ecosystem.
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http://dx.doi.org/10.1038/s41598-021-83426-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7895951PMC
February 2021

Is conservation based on best available science creating an ecological trap for an imperiled lagomorph?

Ecol Evol 2021 Jan 19;11(2):912-930. Epub 2020 Dec 19.

Department of Environmental and Forest Biology SUNY College of Environmental Science and Forestry Syracuse NY USA.

Habitat quality regulates fitness and population density, making it a key driver of population size. Hence, increasing habitat quality is often a primary goal of species conservation. Yet, assessments of fitness and density are difficult and costly to obtain. Therefore, species conservation often uses "best available science," extending inferences across taxa, space, or time, and inferring habitat quality from studies of habitat selection. However, there are scenarios where habitat selection is not reflective of habitat quality, and this can lead to maladaptive management strategies. The New England cottontail () is an imperiled shrubland obligate lagomorph whose successful recovery hinges on creation of suitable habitat. Recovery of this species is also negatively impacted by the non-native eastern cottontail (), which can competitively exclude New England cottontails from preferred habitat. Herein, we evaluate habitat quality for adult and juvenile New England and eastern cottontails using survival and density as indicators. Our findings did not support selection following an ideal free distribution by New England cottontails. Instead, selected resources, which are a target of habitat management, were associated with low survival and density and pointed to a complex trade-off between density, survival, habitat, and the presence of eastern cottontails. Further, movement distance was inversely correlated with survival in both species, suggesting that habitat fragmentation limits the ability of cottontails to freely distribute based on habitat quality. While habitat did not directly regulate survival of juvenile cottontails, tick burden had a strong negative impact on juvenile cottontails in poor body condition. Given the complex interactions among New England cottontails, eastern cottontails, and habitat, directly assessing and accounting for factors that limit New England cottontail habitat quality in management plans is vital to their recovery. Our study demonstrates an example of management for possible ecological trap conditions via the application of incomplete knowledge.
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http://dx.doi.org/10.1002/ece3.7104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7820145PMC
January 2021

Implications of Insecticide-Treated Mosquito Net Fishing in Lower Income Countries.

Environ Health Perspect 2021 01 8;129(1):15001. Epub 2021 Jan 8.

Department of Environmental and Global Health and Center for Environmental and Human Toxicology, University of Florida, Gainesville, Florida, USA.

Introduction: Insecticide-treated mosquito nets (ITNs) are highly effective for the control of malaria. Yet widely distributed ITNs have been repurposed as fishing nets throughout the world.

Objectives: Herein we present a synthesis of the current knowledge of ITN fishing and the toxicity of pyrethroids and discuss the potential implications of widespread fishing with ITNs. We further review effective management strategies in tropical fisheries to explore a framework for managing potential ITN fishing impacts.

Discussion: Pyrethroids are toxic to fish and aquatic environments, and fishing with ITNs may endanger the health of fisheries. Furthermore, although human toxicity to the pyrethroid insecticides that impregnate ITNs is traditionally thought to be low, recent scientific advances have shown that pyrethroid exposure is associated with a host of human health issues, including neurocognitive developmental disorders, diabetes, and cardiovascular disease. Although it is known that ITN fishing is widespread, the implications for both fisheries and human communities is understudied and may be severe. https://doi.org/10.1289/EHP7001.
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http://dx.doi.org/10.1289/EHP7001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7793550PMC
January 2021

Exploring the Niche of Rickettsia montanensis (Rickettsiales: Rickettsiaceae) Infection of the American Dog Tick (Acari: Ixodidae), Using Multiple Species Distribution Model Approaches.

J Med Entomol 2021 05;58(3):1083-1092

Quantitative Disease Ecology and Conservation (QDEC) Lab Group, Department of Geography, University of Florida, Gainesville, FL.

The American dog tick, Dermacentor variabilis (Say) (Acari: Ixodidae), is a vector for several human disease-causing pathogens such as tularemia, Rocky Mountain spotted fever, and the understudied spotted fever group rickettsiae (SFGR) infection caused by Rickettsia montanensis. It is important for public health planning and intervention to understand the distribution of this tick and pathogen encounter risk. Risk is often described in terms of vector distribution, but greatest risk may be concentrated where more vectors are positive for a given pathogen. When assessing species distributions, the choice of modeling framework and spatial layers used to make predictions are important. We first updated the modeled distribution of D. variabilis and R. montanensis using maximum entropy (MaxEnt), refining bioclimatic data inputs, and including soil variables. We then compared geospatial predictions from five species distribution modeling frameworks. In contrast to previous work, we additionally assessed whether the R. montanensis positive D. variabilis distribution is nested within a larger overall D. variabilis distribution, representing a fitness cost hypothesis. We found that 1) adding soil layers improved the accuracy of the MaxEnt model; 2) the predicted 'infected niche' was smaller than the overall predicted niche across all models; and 3) each model predicted different sizes of suitable niche, at different levels of probability. Importantly, the models were not directly comparable in output style, which could create confusion in interpretation when developing planning tools. The random forest (RF) model had the best measured validity and fit, suggesting it may be most appropriate to these data.
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http://dx.doi.org/10.1093/jme/tjaa263DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8122238PMC
May 2021

Building resilience to mosquito-borne diseases in the Caribbean.

PLoS Biol 2020 11 24;18(11):e3000791. Epub 2020 Nov 24.

Inter-American Institute for Global Change Research, Montevideo, Department of Montevideo, Uruguay.

Small island developing states in the Caribbean are among the most vulnerable countries on the planet to climate variability and climate change. In the last 3 decades, the Caribbean region has undergone frequent and intense heat waves, storms, floods, and droughts. This has had a detrimental impact on population health and well-being, including an increase in infectious disease outbreaks. Recent advances in climate science have enhanced our ability to anticipate hydrometeorological hazards and associated public health challenges. Here, we discuss progress towards bridging the gap between climate science and public health decision-making in the Caribbean to build health system resilience to extreme climatic events. We focus on the development of climate services to help manage mosquito-transmitted disease epidemics. There are numerous areas of ongoing biological research aimed at better understanding the direct and indirect impacts of climate change on the transmission of mosquito-borne diseases. Here, we emphasise additional factors that affect our ability to operationalise this biological understanding. We highlight a lack of financial resources, technical expertise, data sharing, and formalised partnerships between climate and health communities as major limiting factors to developing sustainable climate services for health. Recommendations include investing in integrated climate, health and mosquito surveillance systems, building regional and local human resource capacities, and designing national and regional cross-sectoral policies and national action plans. This will contribute towards achieving the Sustainable Development Goals (SDGs) and maximising regional development partnerships and co-benefits for improved health and well-being in the Caribbean.
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http://dx.doi.org/10.1371/journal.pbio.3000791DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7685446PMC
November 2020

Ungulate use of locally infectious zones in a re-emerging anthrax risk area.

R Soc Open Sci 2020 Oct 21;7(10):200246. Epub 2020 Oct 21.

Spatial Epidemiology and Ecology Research Laboratory, University of Florida, Gainesville, FL, USA.

Environmentally mediated indirect pathogen transmission is linked to host movement and foraging in areas where pathogens are maintained in the environment. In the case of anthrax, spores of the causative bacterium are released into the environment following host death and create locally infectious zones (LIZs) around carcass sites; by grazing at LIZs, herbivores are potentially exposed to spores. Here, we used camera traps to assess how ungulate species use carcass sites in southwestern Montana and evaluated how these behaviours may promote indirect anthrax transmission, thus providing, to our knowledge, the first detailed documentation and study of the fine-scale mechanisms underlying foraging-based disease transmission in this ecosystem. We found that carcasses at LIZs significantly increased aboveground biomass of vegetation and concentrations of sodium and phosphorus, potentially making these sites more appealing to grazers. Host behavioural responses to LIZs varied depending on species, sex, season and carcass age; but, overall, our results demonstrated that carcasses or carcass sites serve as an attractant to herbivores in this system. Attraction to LIZs probably represents an increased risk of exposure to and, consequently, increased anthrax transmission rates. Accordingly, continued anthrax surveillance and control strategies are critical in this system.
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http://dx.doi.org/10.1098/rsos.200246DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7657905PMC
October 2020

Warming temperatures could expose more than 1.3 billion new people to Zika virus risk by 2050.

Glob Chang Biol 2021 Jan 28;27(1):84-93. Epub 2020 Oct 28.

Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, USA.

In the aftermath of the 2015 pandemic of Zika virus (ZIKV), concerns over links between climate change and emerging arboviruses have become more pressing. Given the potential that much of the world might remain at risk from the virus, we used a previously established temperature-dependent transmission model for ZIKV to project climate change impacts on transmission suitability risk by mid-century (a generation into the future). Based on these model predictions, in the worst-case scenario, over 1.3 billion new people could face suitable transmission temperatures for ZIKV by 2050. The next generation will face substantially increased ZIKV transmission temperature suitability in North America and Europe, where naïve populations might be particularly vulnerable. Mitigating climate change even to moderate emissions scenarios could significantly reduce global expansion of climates suitable for ZIKV transmission, potentially protecting around 200 million people. Given these suitability risk projections, we suggest an increased priority on research establishing the immune history of vulnerable populations, modeling when and where the next ZIKV outbreak might occur, evaluating the efficacy of conventional and novel intervention measures, and increasing surveillance efforts to prevent further expansion of ZIKV.
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http://dx.doi.org/10.1111/gcb.15384DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7756632PMC
January 2021

Climate change could shift disease burden from malaria to arboviruses in Africa.

Lancet Planet Health 2020 09;4(9):e416-e423

Department of Pediatrics, Stanford University, Stanford, CA, USA.

Malaria is a long-standing public health problem in sub-Saharan Africa, whereas arthropod-borne viruses (arboviruses) such as dengue and chikungunya cause an under-recognised burden of disease. Many human and environmental drivers affect the dynamics of vector-borne diseases. In this Personal View, we argue that the direct effects of warming temperatures are likely to promote greater environmental suitability for dengue and other arbovirus transmission by Aedes aegypti and reduce suitability for malaria transmission by Anopheles gambiae. Environmentally driven changes in disease dynamics will be complex and multifaceted, but given that current public efforts are targeted to malaria control, we highlight Ae aegypti and dengue, chikungunya, and other arboviruses as potential emerging public health threats in sub-Saharan Africa.
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http://dx.doi.org/10.1016/S2542-5196(20)30178-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7490804PMC
September 2020

Mapping Thermal Physiology of Vector-Borne Diseases in a Changing Climate: Shifts in Geographic and Demographic Risk of Suitability.

Authors:
Sadie J Ryan

Curr Environ Health Rep 2020 12;7(4):415-423

Quantitative Disease Ecology and Conservation (QDEC) Lab, Department of Geography, University of Florida, Gainesville, FL, 32611, USA.

Purpose Of Review: To describe a collection of recent work published on thermal suitability for vector-borne diseases, in which mapping approaches illustrated the geographic shifts, and spatial approaches describe the demographic impact anticipated with a changing climate.

Recent Findings: While climate change predictions of warming indicate an expansion in VBD suitability risk in some parts of the globe, while in others, optimal temperatures for transmission may be exceeded, as seen for malaria in Western Africa, resulting in declining risk. The thermal suitability of specific vector-pathogen pairs can have large impacts on geographic range of risk, and changes in human demography itself will intersect with this risk to create different vulnerability profiles over the coming century. Using a physiological approach to describe the thermal suitability of transmission for vector-borne diseases allows us to illustrate the future risk as mapped information. This in turn can be coupled with demographic projections to anticipate changing risk, and even changing vulnerability within that population change.
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http://dx.doi.org/10.1007/s40572-020-00290-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7748992PMC
December 2020

Comparing prioritization strategies for delivering indoor residual spray (IRS) implementation, using a network approach.

Malar J 2020 Sep 4;19(1):326. Epub 2020 Sep 4.

Department of Public Health, Syracuse University, Syracuse, NY, 13210, USA.

Background: Indoor residual spraying (IRS) is an effective method to control malaria-transmitting Anopheles mosquitoes and often complements insecticide-treated mosquito nets, the predominant malaria vector control intervention. With insufficient funds to cover every household, malaria control programs must balance the malaria risk to a particular human community against the financial cost of spraying that community. This study creates a framework for modelling the distance to households for targeting IRS implementation, and applies it to potential risk prioritization strategies in four provinces (Luapula, Muchinga, Eastern, and Northern) in Zambia.

Methods: Optimal network models were used to assess the travel distance of routes between operations bases and human communities identified through remote sensing. Network travel distances were compared to Euclidean distances, to demonstrate the importance of accounting for road routes. The distance to reaching communities for different risk prioritization strategies were then compared assuming sufficient funds to spray 50% of households, using four underlying malarial risk maps: (a) predicted Plasmodium falciparum parasite rate in 2-10 years olds (PfPR), or (b) predicted probability of the presence of each of three main malaria transmitting anopheline vectors (Anopheles arabiensis, Anopheles funestus, Anopheles gambiae).

Results: The estimated one-way network route distance to reach communities to deliver IRS ranged from 0.05 to 115.69 km. Euclidean distance over and under-estimated these routes by - 101.21 to 41.79 km per trip, as compared to the network route method. There was little overlap between risk map prioritization strategies, both at a district-by-district scale, and across all four provinces. At both scales, agreement for inclusion or exclusion from IRS across all four prioritization strategies occurred in less than 10% of houses. The distances to reaching prioritized communities were either lower, or not statistically different from non-prioritized communities, at both scales of strategy.

Conclusion: Variation in distance to targeted communities differed depending on risk prioritization strategy used, and higher risk prioritization did not necessarily translate into greater distances in reaching a human community. These findings from Zambia suggest that areas with higher malaria burden may not necessarily be more remote than areas with lower malaria burden.
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http://dx.doi.org/10.1186/s12936-020-03398-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7650283PMC
September 2020

Misconceptions about weather and seasonality must not misguide COVID-19 response.

Nat Commun 2020 08 27;11(1):4312. Epub 2020 Aug 27.

Quantitative Disease Ecology and Conservation (QDEC) Lab, Department of Geography and the Emerging Pathogens Institute, University of Florida, Gainesville, FL, 32610, USA.

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http://dx.doi.org/10.1038/s41467-020-18150-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7452887PMC
August 2020

Predicting the fundamental thermal niche of crop pests and diseases in a changing world: A case study on citrus greening.

J Appl Ecol 2019 Aug 1;56(8):2057-2068. Epub 2019 Jul 1.

Department of Statistics, Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, Virginia.

Predicting where crop pests and diseases can occur, both now and in the future under different climate change scenarios, is a major challenge for crop management. One solution is to estimate the fundamental thermal niche of the pest/disease to indicate where establishment is possible. Here, we develop methods for estimating and displaying the fundamental thermal niche of pests and pathogens and apply these methods to Huanglongbing (HLB), a vector-borne disease that is currently threatening the citrus industry worldwide.We derive a suitability metric based on a mathematical model of HLB transmission between tree hosts and its vector , and incorporate the effect of temperature on vectortraits using data from laboratory experiments performed at different temperatures. We validate the model using data on the historical range of HLB.Our model predicts that transmission of HLB is possible between 16 and 33°C with peak transmission at ~25°C. The greatest uncertainty in our suitability metric is associated with the mortality of the vectors at peak transmission, and fecundity at the edges of the thermal range, indicating that these parameters need further experimental work.We produce global thermal niche maps by plotting how many months each location is suitable for establishment of the pest/disease. This analysis reveals that the highest suitability for HLB occurs near the equator in large citrus-producing regions, such as Brazil and South-East Asia. Within the Northern Hemisphere, the Iberian peninsula and California are HLB suitable for up to 7 months of the year and are free of HLB currently. We create a thermal niche map which indicates the places at greatest risk of establishment should a crop disease or pest enter these regions. This indicates where surveillance should be focused to prevent establishment. Our mechanistic method can be used to predict new areas for Huanglongbing transmission under different climate change scenarios and is easily adapted to other vector-borne diseases and crop pests.
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http://dx.doi.org/10.1111/1365-2664.13455DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7367095PMC
August 2019

Spatial variation in the frequency of knockdown resistance genotypes in Florida Aedes aegypti populations.

Parasit Vectors 2020 May 11;13(1):241. Epub 2020 May 11.

Quantitative Disease Ecology and Conservation (QDEC) Lab, Department of Geography, University of Florida, Gainesville, FL, 32607, USA.

Background: The development of insecticide resistance in disease-vectoring mosquito species can lead to vector control failure and disease resurgence. However, insecticide applications remain an essential public health intervention. In Florida, insecticide resistance in Aedes aegypti, an anthropophilic mosquito species capable of transmitting dengue, chikungunya, and Zika virus, is a major concern. Understanding the location, scale, and driving factors of insecticide resistance can enhance the ability of vector control organizations to target populations effectively.

Methods: We used previously collected data on frequencies of mutations that confer resistance to commonly used pyrethroid insecticides in Ae. aegypti specimens from 62 sites distributed across 18 counties in Florida. To determine the scale of clustering for the most resistant variant, we used a Ripley's K function. We also used a spatial scanning statistic technique to identify locations of clusters where higher than expected frequencies of susceptible or resistant mosquitoes occurred. We then tested for associations between landscape, demographic, and insecticide-use factors using a beta regression modelling approach and evaluated the effect of spatial lag and spatial error terms on overall explanatory power of these models.

Results: The scale at which maximum clustering of the most resistant variant occurs is approximately 20 kilometers. We identified statistically significant clusters of genotypes associated with resistance in several coastal cities, although some of these clusters were near significant clusters of susceptible mosquitoes, indicating selection pressures vary at the local scale. Vegetation density, distance from roads, and pyrethroid-use by vector control districts were consistently significant predictors of knockdown resistance genotype frequency in the top-performing beta regression models, although pyrethroid use surprisingly had a negatively associated with resistance. The incorporation of spatial lags resulted in improvements to the fit and explanatory power of the models, indicating an underlying diffusion process likely explains some of the spatial patterns observed.

Conclusions: The genetic mutations that confer resistance to pyrethroids in Ae. aegypti mosquitoes in Florida exhibit spatial autocorrelation and patterns that can be partially explained by landscape and insecticide-use factors. Further work at local scales should be able to identify the mechanisms by which these variables influence selection for alleles associated with resistance.
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http://dx.doi.org/10.1186/s13071-020-04112-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7216362PMC
May 2020

Shifting transmission risk for malaria in Africa with climate change: a framework for planning and intervention.

Malar J 2020 May 1;19(1):170. Epub 2020 May 1.

Chemonics International, Washington, DC, USA.

Background: Malaria continues to be a disease of massive burden in Africa, and the public health resources targeted at surveillance, prevention, control, and intervention comprise large outlays of expense. Malaria transmission is largely constrained by the suitability of the climate for Anopheles mosquitoes and Plasmodium parasite development. Thus, as climate changes, shifts in geographic locations suitable for transmission, and differing lengths of seasons of suitability will occur, which will require changes in the types and amounts of resources.

Methods: The shifting geographic risk of malaria transmission was mapped, in context of changing seasonality (i.e. endemic to epidemic, and vice versa), and the number of people affected. A published temperature-dependent model of malaria transmission suitability was applied to continental gridded climate data for multiple future AR5 climate model projections. The resulting outcomes were aligned with programmatic needs to provide summaries at national and regional scales for the African continent. Model outcomes were combined with population projections to estimate the population at risk at three points in the future, 2030, 2050, and 2080, under two scenarios of greenhouse gas emissions (RCP4.5 and RCP8.5).

Results: Estimated geographic shifts in endemic and seasonal suitability for malaria transmission were observed across all future scenarios of climate change. The worst-case regional scenario (RCP8.5) of climate change predicted an additional 75.9 million people at risk from endemic (10-12 months) exposure to malaria transmission in Eastern and Southern Africa by the year 2080, with the greatest population at risk in Eastern Africa. Despite a predominance of reduction in season length, a net gain of 51.3 million additional people is predicted be put at some level of risk in Western Africa by midcentury.

Conclusions: This study provides an updated view of potential malaria geographic shifts in Africa under climate change for the more recent climate model projections (AR5), and a tool for aligning findings with programmatic needs at key scales for decision-makers. In describing shifting seasonality, it was possible to capture transitions between endemic and epidemic risk areas, to facilitate the planning for interventions aimed at year-round risk versus anticipatory surveillance and rapid response to potential outbreak locations.
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http://dx.doi.org/10.1186/s12936-020-03224-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7193356PMC
May 2020

Spatiotemporal Tools for Emerging and Endemic Disease Hotspots in Small Areas: An Analysis of Dengue and Chikungunya in Barbados, 2013-2016.

Am J Trop Med Hyg 2020 07 23;103(1):149-156. Epub 2020 Apr 23.

Emerging Pathogens Institutue, University of Florida, Gainesville, Florida.

Dengue fever and other febrile mosquito-borne diseases place considerable health and economic burdens on small island nations in the Caribbean. Here, we used two methods of cluster detection to find potential hotspots of transmission of dengue and chikungunya in Barbados, and to assess the impact of input surveillance data and methodology on observed patterns of risk. Using Moran's I and spatial scan statistics, we analyzed the geospatial and temporal distribution of disease cases and rates across Barbados for dengue fever in 2013-2016, and a chikungunya outbreak in 2014. During years with high numbers of dengue cases, hotspots for cases were found with Moran's I in the south and central regions in 2013 and 2016, respectively. Using smoothed disease rates, clustering was detected in all years for dengue. Hotspots suggesting higher rates were not detected via spatial scan statistics, but coldspots suggesting lower than expected rates of disease activity were found in southwestern Barbados during high case years of dengue. No significant spatiotemporal structure was found in cases during the chikungunya outbreak. Spatial analysis of surveillance data is useful in identifying outbreak hotspots, potentially complementing existing early warning systems. We caution that these methods should be used in a manner appropriate to available data and reflecting explicit public health goals-managing for overall case numbers or targeting anomalous rates for further investigation.
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http://dx.doi.org/10.4269/ajtmh.19-0919DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7356414PMC
July 2020

Key Findings and Comparisons From Analogous Case-Cluster Studies for Dengue Virus Infection Conducted in Machala, Ecuador, and Kamphaeng Phet, Thailand.

Front Public Health 2020 12;8. Epub 2020 Feb 12.

Department of Medicine, SUNY Upstate Medical University, Syracuse, NY, United States.

Dengue viruses (DENV) pose a significant and increasing threat to human health across broad regions of the globe. Currently, prevention, control, and treatment strategies are limited. Promising interventions are on the horizon, including multiple vaccine candidates under development and a renewed and innovative focus on controlling the vector, . However, significant gaps persist in our understanding of the similarities and differences in DENV epidemiology across regions of potential implementation and evaluation. In this manuscript, we highlight and compare findings from two analogous cluster-based studies for DENV transmission and pathogenesis conducted in Thailand and Ecuador to identify key features and questions for further pursuit. Despite a remarkably similar incidence of DENV infection among enrolled neighborhood contacts at the two sites, we note a higher occurrence of secondary infection and severe illness in Thailand compared to Ecuador. A higher force of infection in Thailand, defined as the incidence of infection among susceptible individuals, is suggested by the higher number of captured mosquitoes per household, the increasing proportion of asymptomatic infections with advancing age, and the high proportion of infections identified as secondary-type infections by serology. These observations should be confirmed in long-term, parallel prospective cohort studies conducted across regions, which would advantageously permit characterization of baseline immune status (susceptibility) and contemporaneous assessment of risks and risk factors for dengue illness.
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http://dx.doi.org/10.3389/fpubh.2020.00002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7028768PMC
May 2021

Severity Index for Suspected Arbovirus (SISA): Machine learning for accurate prediction of hospitalization in subjects suspected of arboviral infection.

PLoS Negl Trop Dis 2020 02 14;14(2):e0007969. Epub 2020 Feb 14.

Institute for Global Health and Translational Science, SUNY Upstate Medical University, Syracuse, New York, United States of America.

Background: Dengue, chikungunya, and Zika are arboviruses of major global health concern. Decisions regarding the clinical management of suspected arboviral infection are challenging in resource-limited settings, particularly when deciding on patient hospitalization. The objective of this study was to determine if hospitalization of individuals with suspected arboviral infections could be predicted using subject intake data.

Methodology/principal Findings: Two prediction models were developed using data from a surveillance study in Machala, a city in southern coastal Ecuador with a high burden of arboviral infections. Data were obtained from subjects who presented at sentinel medical centers with suspected arboviral infection (November 2013 to September 2017). The first prediction model-called the Severity Index for Suspected Arbovirus (SISA)-used only demographic and symptom data. The second prediction model-called the Severity Index for Suspected Arbovirus with Laboratory (SISAL)-incorporated laboratory data. These models were selected by comparing the prediction ability of seven machine learning algorithms; the area under the receiver operating characteristic curve from the prediction of a test dataset was used to select the final algorithm for each model. After eliminating those with missing data, the SISA dataset had 534 subjects, and the SISAL dataset had 98 subjects. For SISA, the best prediction algorithm was the generalized boosting model, with an AUC of 0.91. For SISAL, the best prediction algorithm was the elastic net with an AUC of 0.94. A sensitivity analysis revealed that SISA and SISAL are not directly comparable to one another.

Conclusions/significance: Both SISA and SISAL were able to predict arbovirus hospitalization with a high degree of accuracy in our dataset. These algorithms will need to be tested and validated on new data from future patients. Machine learning is a powerful prediction tool and provides an excellent option for new management tools and clinical assessment of arboviral infection.
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http://dx.doi.org/10.1371/journal.pntd.0007969DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7046343PMC
February 2020

A network analysis framework to improve the delivery of mosquito abatement services in Machala, Ecuador.

Int J Health Geogr 2020 02 11;19(1). Epub 2020 Feb 11.

Quantitative Disease Ecology and Conservation (QDEC) Lab Group, Department of Geography, University of Florida, Gainesville, FL, USA.

Background: Vector-borne disease places a high health and economic burden in the American tropics. Comprehensive vector control programs remain the primary method of containing local outbreaks. With limited resources, many vector control operations struggle to serve all affected communities within their districts. In the coastal city of Machala, Ecuador, vector control services, such as application of larvicides and truck-mounted fogging, are delivered through two deployment facilities managed by the Ecuadorian Ministry of Health. Public health professionals in Machala face several logistical issues when delivering mosquito abatement services, namely applying limited resources in ways that will most effectively suppress vectors of malaria, dengue, and encephalitis viruses.

Methods: Using a transportation network analysis framework, we built models of service areas and optimized delivery routes based on distance costs associated with accessing neighborhoods throughout the city. Optimized routes were used to estimate the relative cost of accessing neighborhoods for mosquito control services in Machala, creating a visual tool to guide decision makers and maximize mosquito control program efficiency. Location-allocation analyses were performed to evaluate efficiency gains of moving service deployment to other available locations with respect to distance to service hub, neighborhood population, dengue incidence, and housing condition.

Results: Using this framework, we identified different locations for targeting mosquito control efforts, dependent upon management goals and specified risk factors of interest, including human population, housing condition, and reported dengue incidence. Our models indicate that neighborhoods on the periphery of Machala with the poorest housing conditions are the most costly to access. Optimal locations of facilities for deployment of control services change depending on pre-determined management priorities, increasing the population served via inexpensive routes up to 34.9%, and reducing overall cost of accessing neighborhoods up to 12.7%.

Conclusions: Our transportation network models indicate that current locations of mosquito control facilities in Machala are not ideal for minimizing driving distances or maximizing populations served. Services may be optimized by moving vector control operations to other existing public health facilities in Machala. This work represents a first step in creating a spatial tool for planning and critically evaluating the systematic delivery of mosquito control services in Machala and elsewhere.
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http://dx.doi.org/10.1186/s12942-020-0196-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7014633PMC
February 2020

A generic arboviral model framework for exploring trade-offs between vector control and environmental concerns.

J Theor Biol 2020 04 14;490:110161. Epub 2020 Jan 14.

Department of Ecology & Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, United States; National Institute for Mathematical and Biological Synthesis (NIMBioS), University of Tennessee, Knoxville, TN 37996, United States; Department of Mathematics, University of Tennessee, Knoxville, TN 37996, United States.

Effective public health measures must balance potentially conflicting demands from populations they serve. In the case of infectious disease risks from mosquito-borne infections, such as Zika virus, public concern about the pathogen may be counterbalanced by public concern about environmental contamination from chemical agents used for vector control. Here we introduce a generic framework for modeling how the spread of an infectious pathogen might lead to varying public perceptions, and therefore tolerance, of both disease risk and pesticide use. We consider how these dynamics might impact the spread of a vector-borne disease. We tailor and parameterize our model for direct application to Zika virus as spread by Aedes aegypti mosquitoes, though the framework itself has broad applicability to any arboviral infection. We demonstrate how public risk perception of both disease and pesticides may drastically impact the spread of a mosquito-borne disease in a susceptible population. We conclude that models hoping to inform public health decision making about how best to mitigate arboviral disease risks should explicitly consider the potential public demand for, or rejection of, chemical control of mosquito populations.
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http://dx.doi.org/10.1016/j.jtbi.2020.110161DOI Listing
April 2020
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