Biology subjects

Ryan, S. J.

Publications and source records attributed to Ryan, S. J..

12 recordsLinked to original sources

bioRxiv2018

Minimum Information for Reusable Arthropod Abundance Data (MIReAAD)

Introduction Introduction Discussion Conclusion References Arthropods play a dominant role in the dynamics of practically all natural and human-modified terrestrial ecosystems1-3, and have significant economic and health effects. For example, certain insects provide significant economic benefits (e.g. pollination) exceeding $57 billion a year to the United States alone4. Meanwhile, invasive insects cost an estimated $70 billion dollars per year globally5 and insect pests may reduce agricultural harvests by up to 16%, with an equal amount of further losses of harvested goods6. Particularly noteworthy is a subset of arthropods that are disease vectors, transmitting pathogens to and between animals as well as plan ...

ecology↗

bioRxiv2018

Geographic shifts in Aedes aegypti habitat suitability in Ecuador using larval surveillance data and ecological niche modeling: implications of climate change for public health vector control

Arboviral disease transmission by Aedes mosquitoes poses a major challenge to public health systems in Ecuador, where constraints on health services and resource allocation call for spatially informed management decisions. Employing a unique dataset of larval occurrence records provided by the Ecuadorian Ministry of Health, we used ecological niche models (ENMs) to estimate the current geographic distribution of Aedes aegypti in Ecuador, using mosquito presence as a proxy for risk of disease transmission. ENMs built with the Genetic Algorithm for Rule-Set Production (GARP) algorithm and a suite of environmental variables were assessed for agreement and accuracy. The top model of larval mosquito presence was projected to the year 2050 under various combinations of greenhouse gas emissions scenarios and models of climate change. Under current climatic conditions, larval mosquitoes were not predicted in areas of high elevation in Ecuador, such as the Andes mountain range, as well as the eastern portion of the Amazon basin. However, all models projected to scenarios of future climate change demonstrated potential shifts in mosquito distribution, wherein range contractions were seen throughout most of eastern Ecuador, and areas of transitional elevation became suitable for mosquito presence. Encroachment of Ae. aegypti into mountainous terrain was estimated to affect up to 4,215 km2 under the most extreme scenario of climate change, an area which would put over 12,000 people currently living in transitional areas at risk. This distributional shift into communities at higher elevations indicates an area of concern for public health agencies, as targeted interventions may be needed to protect vulnerable populations with limited prior exposure to mosquito-borne diseases. Ultimately, the results of this study serve as a tool for informing public health policy and mosquito abatement strategies in Ecuador.\n\nAuthor summaryThe yellow fever mosquito (Aedes aegypti) is a medically important vector of arboviral diseases in Ecuador, such as dengue fever and chikungunya. Managing Ae. aegypti is a challenge to public health agencies in Latin America, where the use of limited resources must be planned in an efficient, targeted manner. The spatial distribution of Ae. aegypti can be used as a proxy for risk of disease exposure, guiding policy formation and decision-making. We used ecological niche models in this study to predict the range of Ae. aegypti in Ecuador, based on agency larval mosquito surveillance records and layers of environmental predictors (e.g. climate, altitude, and human population). The best models of current range were then projected to the year 2050 under a variety of greenhouse gas emissions scenarios and models of climate change. All modeled future scenarios predicted shifts in the range of Ae. aegypti, allowing us to assess human populations that may be at risk of becoming exposed to Aedes vectored diseases. As climate changes, we predict that communities living in areas of transitional elevation along the Andes mountain range are vulnerable to the expansion of Aedes aegypti.

epidemiology↗

bioRxiv2018

Environmental drivers of ranavirus in free living amphibians in constructed ponds.

Amphibian ranaviruses occur globally, but we are only beginning to understand mechanisms for emergence. Ranaviruses are aquatic pathogens which can cause > 90% mortality in larvae of many aquatic-breeding amphibians, making them important focal host taxa. Host susceptibilities and virulence of ranaviruses have been studied extensively in controlled laboratory settings, but research is needed to identify drivers of infection in natural environments. Constructed ponds, essential components of wetland restoration, have been associated with higher ranavirus prevalence than natural ponds, posing a conundrum for conservation efforts, and emphasizing the need to understand potential drivers. In this study, we analyzed four years of Frog virus 3 prevalence and associated environmental parameters in populations of wood frogs (Lithobates sylvaticus) and green frogs (Lithobates clamitans) in a constructed pond system. High prevalence was best predicted by low temperature, high host density, low zooplankton concentrations, and Gosner stages approaching metamorphosis. This study identified important variables to measure in assessments of ranaviral infection risk in newly constructed ponds, including effects of zooplankton, which have not been previously quantified in natural settings. Examining factors mediating diseases in natural environments, particularly in managed conservation settings, is important to both validate laboratory findings in situ, and to inform future conservation planning, particularly in the context of adaptive management.

ecology↗

bioRxiv2018

Temperature explains broad patterns of Ross River virus transmission across Australia

Temperature impacts the physiology of ectotherms, including vectors that transmit disease. While thermal biology predicts nonlinear effects of temperature on vector and pathogen traits that drive disease transmission, the empirical relationship between temperature and transmission remains unknown for most vector-borne pathogens. We built a mechanistic model to estimate the thermal response of Ross River virus, an important mosquito-borne pathogen of humans in Australia, the Pacific Islands, and potentially emerging worldwide. Transmission peaks at moderate temperatures (26.4{degrees}C) and declines to zero at low (17.0{degrees}C) and high (31.5{degrees}C) temperatures. The model predicted broad patterns of disease across Australia. First, transmission is year-round endemic in the tropics and sub-tropics but seasonal in temperate zones. Second, nationwide human cases peak seasonally as predicted from population-weighted seasonal temperatures. These results illustrate the importance of nonlinear, mechanistic models for inferring the role of temperature in disease dynamics and predicting responses to climate change.

ecology↗

bioRxiv2018

Zika Virus Outbreak, Barbados, 2015 - 2016

Barbados is a Caribbean island country of approximately 285,000 people, with a thriving tourism industry. In 2015, Zika spread rapidly throughout the Americas, and its proliferation through the Caribbean islands followed suit. Barbados reported its first confirmed autochthonous Zika transmission to the Pan American Health Organization (PAHO) in January 2016, a month before the global public health emergency was declared. Following detection of suspected Zika cases on Barbados in 2015, 926 individuals were described as suspected cases, and 147 lab confirmed cases were reported through December 2016, the end of the most recent epidemiological year. In this short report, we describe the epidemiological characteristics of 926 clinical case records which were originally suspected as cases of Zika, and which were subsequently sent for testing and confirmation; 147 were found positive for Zika, using RT-PCR methods, another 276 tested negative, and the remaining 503 were either pending results or still in the suspected category. Women were represented at about twice the rate of men in case records where sex was reported (71.9%), and confirmed cases (78.2%), and 19 of the confirmed positive cases were children under the age of 10.

epidemiology↗

bioRxiv2017

Quantifying Seasonal and Diel Variation in Anopheline and Culex Human Biting Rates in Southern Ecuador

BackgroundQuantifying mosquito biting rates for specific locations enables estimation of mosquito-borne disease risk, and can inform intervention efforts. Measuring biting itself is fraught with ethical concerns, so the landing rate of mosquitoes on humans is often used as a proxy measure. Southern coastal Ecuador was historically endemic for malaria (P. falciparum and P. vivax), although successful control efforts in the 2000s eliminated autochthonous transmission (since 2011). This study presents an analysis of data collected during the elimination period.\n\nMethodsWe examined human landing catch (HLC) data for three mosquito taxa: 2 malaria vectors, Anopheles albimanus and Anopheles punctimacula, and grouped Culex spp. These data were collected by the National Vector Control Service of the Ministry of Health over a 5-year time span (2007 - 2012) in five cities in southern coastal Ecuador, at multiple households, in all months of the year, during dusk-dawn (18:00-6:00) hours, often at both indoor and outdoor locations. Hurdle models were used to determine if biting activity was fundamentally different for the three taxa, and to identify spatial and temporal factors influencing bite rate. Due to the many different approaches to studying and quantifying bite rates in the literature, we also created a glossary of terms, to facilitate comparative studies in the future.\n\nResultsBiting trends varied significantly with species and time. All taxa exhibited exophagic feeding behavior, and outdoor locations increased both the odds and incidence of bites across taxa. An. albimanus was most frequently observed biting, with an average of 4.7 bites per hour. The highest and lowest respective months for significant biting activity were March and July for An. albimanus, July and August for An. punctimacula, and February and July for Culex spp.\n\nConclusionsFine-scale spatial and temporal differences exist in biting patterns among mosquito taxa in southern coastal Ecuador. This analysis provides detailed information for targeting vector control and household level behavioral interventions. These data were collected as part of routine vector surveillance conducted by the Ministry of Health, but such data have not been collected since. Reinstating such surveillance measures would provide important information to aid in preventing malaria re-emergence.

epidemiology↗

bioRxiv2017

Climate change drives uncertain global shifts in potential distribution and seasonal risk of Aedes-transmitted viruses

AbstractForecasting the impacts of climate change on Aedes-borne viruses--especially dengue, chikungunya, and Zika--is a key component of public health preparedness. We apply an empirically parameterized Bayesian transmission model of Aedes-borne viruses for the two vectors Aedes aegypti and Ae. albopictus as a function of temperature to predict cumulative monthly global transmission risk in current climates, and compare with projected risk in 2050 and 2080 based on general circulation models (GCMs). Our results show that if mosquito range shifts track optimal temperatures for transmission (26-29 {degrees}C), we can expect poleward shifts in Aedes-borne virus distributions. However, the differing thermal niches of the two vectors produce different patterns of shifts under climate change. More severe climate change scenarios produce proportionally worse population exposures from Ae. aegypti, but not from Ae. albopictus in the most extreme cases. Expanding risk of transmission from both mosquitoes will likely be a serious problem, even in the short term, for most of Europe; but significant reductions are also expected for Aedes albopictus, most noticeably in southeast Asia and west Africa. Within the next century, nearly a billion people are threatened with new exposure to both Aedes spp. in the worst-case scenario; but massive net losses in risk are noticeable for Ae. albopictus, especially in terms of year-round transmission, marking a global shift towards more seasonal risk across regions. Many other complicating factors (like mosquito range limits and viral evolution) exist, but overall our results indicate that while climate change will lead to both increased and new exposures to vector-borne disease, the most extreme increases in Ae. albopictus transmission are predicted to occur at intermediate climate change scenarios.\n\nAuthor SummaryThe established scientific consensus indicates that climate change will severely exacerbate the risk and burden of Aedes-transmitted viruses, including dengue, chikungunya, Zika, West Nile virus, and other significant threats to global health security. Here, we show that the story is more complicated, first and foremost due to differences between the more heat-tolerant Aedes aegypti and the more heat-limited Ae. albopictus. Almost a billion people could face their first exposure to viral transmission from either mosquito in the worst-case scenario, especially in Europe and high-elevation tropical and subtropical regions. On the other hand, while year-round transmission potential from Ae. aegypti is likely to expand (especially in south Asia and sub-Saharan Africa), Ae. albopictus loses significant ground in the tropics, marking a global shift towards seasonal risk as the tropics eventually become too hot for transmission by Ae. albopictus. Complete mitigation of climate change to a pre-industrial baseline could protect almost a billion people from arbovirus range expansions; but middle-of-the-road mitigation may actually produce the greatest expansion in the potential for viral transmission by Ae. albopictus. In any scenario, mitigating climate change also shifts the burden of both dengue and chikungunya (and potentially other Aedes transmitted viruses) from higher-income regions back onto the tropics, where transmission might otherwise start to be curbed by rising temperatures.

epidemiology↗

bioRxiv2017

Competition in the savanna: Models of species assemblages in Kruger National Park, South Africa

We examined hypotheses of spatial association arising from direct or indirect competitive interactions, using thirteen years of gridded mammal census data from Kruger National Park, South Africa. As interactions occur at different scales, we explored the data at 1, 5, 10, and 15 km2. We proposed four hypotheses structuring the mammal community: H1. direct competition between carnivores and herbivores; H2-4: indirect competition produced by each of three types of herbivore diet specialization: H2. ruminants and non-ruminants, H3. grazers and browsers, and H4. a four-way division of small and large grazers and browsers. We used the software CoOccur to implement a robus test for evidence of our hypotheses against null models of community assemblage. At 5, 10, and 15km2 scales, the results supported a competition mechanism in the majority of years for hypotheses H1, H3, and H4, and facilitation in H2. At the finest spatial scale (1km2), we saw evidence for a mixture of competitive, neutral and facilitative process. These results suggest strong, large-scale effects of interspecific interactions on distributions of African megafauna, which may not operate at a more local (1km2) scale, underscoring the importance of scale and mechanism in the guild structure of communities.

ecology↗

bioRxiv2017

Dengue fever and Aedes aegypti risk in the Galapagos Islands, Ecuador

IntroductionDengue fever is an emerging infectious disease in the Galapagos Islands of Ecuador, with the first cases reported in 2002 and periodic outbreaks since then. Here we report the results of a pilot study conducted in two cities in 2014: Puerto Ayora (PA) on Santa Cruz Island, and Puerto Baquerizo Moreno (PB) on Santa Cristobal Island. The aims of this study were to assess the social-ecological risk factors associated with dengue and mosquito presence at the household-level.\n\nMethodsIn 2014 we conducted 100 household surveys (50 on each island) in neighborhoods with prior reported dengue. Adult mosquitoes were collected inside and outside the home, larval indices were determined through container surveys, and heads of households were interviewed to determine demographics, prior dengue infections, housing conditions, and knowledge, attitudes and practices regarding dengue. Multimodel selection methods were used to derive best-fit generalized linear regression (GLM) models of prior dengue infection, and the presence of Ae. aegypti in the home.\n\nResultsWe found that 24% of PB and 14% of PA respondents self-reported a prior dengue infection, and more PB homes than PA homes had Ae. aegypti. The top-ranked model for prior dengue infection included human movement - travel between neighborhoods, between islands, and to the mainland; demographics including salary level and education of the head of household, and increase with more people per room in a house, house condition, access to water quality issues, and dengue awareness. The top-ranked model for the presence of Ae. aegypti included housing conditions, including the presence of window screens and air conditioners, mosquito control actions, and dengue risk perception.\n\nDiscussion/conclusionTo our knowledge, this is the first study of dengue risk and Aedes aegypti in the Galapagos Islands. The findings that human movement within and between islands, and to and from the mainland, were important to reported dengue cases confirms concerns of this route of introduction and repeated transmission.

epidemiology↗

bioRxiv2017

The social and spatial ecology of dengue presence and burden during an outbreak in Guayaquil, Ecuador, 2012

Dengue fever, a mosquito-borne viral disease, is an ongoing public health problem in Ecuador and throughout the tropics, yet we have a limited understanding of the disease transmission dynamics in these regions. The objective of this study was to characterize the spatial dynamics and social-ecological risk factors associated with a recent dengue outbreak in Guayaquil, Ecuador. We examined georeferenced dengue cases (n = 4,248) and block-level census data variables to identify potential social-ecological variables associated with the presence and burden of dengue fever in Guayaquil in 2012. We applied LISA and Morans I tests to analyze hotspots of dengue cases and used multimodel selection in R computing language to identify covariates associated with dengue incidence at the census zone level. Significant hotspots of dengue transmission were found near the North Central and Southern portions of Guayaquil. Significant risk factors for presence of dengue included poor housing conditions (e.g., poor condition of ceiling, floors, and walls), access to paved roads, and receipt of remittances. Counterintuitive positive correlations with dengue presence were observed with several municipal services such as garbage collection and access to piped water. Risk factors for the increased burden of dengue included poor housing conditions, garbage collection, receipt of remittances, and sharing a property with more than one household. Social factors such as education and household demographics were negatively correlated with increased dengue burden. Our findings elucidate underlying differences with dengue presence and burden and indicate the potential to develop dengue vulnerability and risk maps to inform disease prevention and control - information that is also relevant for emerging epidemics of chikungunya and zika.\n\nHighlightsO_LIIn 2012, Guayaquil, Ecuador had a large outbreak of dengue cases\nC_LIO_LIDengue case presence and burden exhibited spatial heterogeneity at the census block level\nC_LIO_LISocial-ecological drivers of case presence and burden differed in this outbreak, highlighting the need to model both types of epidemiological data\nC_LIO_LIAccess to municipal resources such as garbage collection and piped water had counterintuitive relationships with dengue presence, but poor housing, garbage collection and remittances correlated to dengue burden.\nC_LIO_LIOur findings inform risk mapping and vector control and surveillance allocation, relevant to this and other concurrent emergent epidemics such as chikungunya and zika\nC_LI

epidemiology↗

bioRxiv2017

Environmental cholera (Vibrio cholerae) dynamics in an estuarine system in southern coastal Ecuador

Cholera emergence is strongly linked to local environmental and ecological context. The 1991-2004 pandemic emerged in Peru and spread north into Ecuadors El Oro province, making this a key site for potential re-emergence. Machala, El Oro, is a port city of 250,000, near the Peruvian border. Many livelihoods depend on the estuarine system, from fishing for subsistence and trade, to domestic water use. In 2014, we conducted biweekly sampling for 10 months in five estuarine locations, across a gradient of human use, and ranging from inland to ocean. We measured water characteristics implicated in V. cholerae growth and persistence: pH, temperature, salinity, and algal concentration, and evaluated samples in five months for pathogenic and non-pathogenic Vibrio cholerae, by polymerase chain reaction (PCR). We found environmental persistence of strains O1 and O139, but no evidence for toxigene presence. V. cholerae presence was coupled to algal and salinity concentration, and sites exhibited considerable seasonal and spatial heterogeneity. This study indicates that environmental conditions in Machala are optimal for human cholera re-emergence, with risk peaking during September, and higher risk near urban periphery low-income communities. This highlights a need for surveillance of this coupled cholera- estuarine system to anticipate potential future outbreaks.

epidemiology↗

bioRxiv2017

The high burden of dengue and chikungunya in southern coastal Ecuador: Epidemiology, clinical presentation, and phylogenetics from a prospective study in Machala in 2014 and 2015

Here we report the findings from the first two years of an arbovirus surveillance study conducted in Machala, Ecuador, a dengue endemic region (2014-2015). Patients with suspected dengue virus (DENV) infections (index cases, n=324) were referred from five Ministry of Health clinical sites. A subset of DENV positive index cases (n = 44) were selected, and individuals from the index household and four neighboring homes within 200-meters were recruited (n = 400). Individuals who entered the study, other than index cases, are referred to as associates. In 2014, 70.9% of index cases and 35.6% of associates had acute or recent DENV infections. In 2015, 28.3% of index cases and 12.8% of associates had acute or recent DENV infections. For every DENV infection captured by passive surveillance, we detected an additional three acute or recent DENV infections in associates. Of associates with acute DENV infections, 68% reported dengue-like symptoms, with the highest prevalence of symptomatic acute infections in children under 10 years of age. The first chikungunya virus (CHIKV) infections were detected on epidemiological week 12 in 2015. 43.1% of index cases and 3.5% of associates had acute CHIKV infections. No Zika virus infections were detected. Phylogenetic analyses of isolates of DENV from 2014 revealed genetic relatedness and shared ancestry of DENV1, DENV2 and DENV4 genomes from Ecuador with those from Venezuela and Colombia, indicating presence of viral flow between Ecuador and surrounding countries. Enhanced surveillance studies, such as this, provide high-resolution data on symptomatic and inapparent infections across the population.

epidemiology↗