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.
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.
GAINESVILLE, FL – Researchers and clinicians in Ecuador face a challenging environment: this biodiverse country is home to many disease hosts and vectors. Particularly, the mosquitoes in Ecuador carry and transmit arboviruses (arthropod-borne viruses). This group includes diseases like dengue, chikungunya, Mayaro virus, yellow fever, and Zika, among others. All are spread by overlapping mosquito species. Aedes aegypti and Aedes albopictus transmit dengue, chikungunya, Zika, Mayaro virus, and yellow fever. Haemagogus and Sabethes mosquitoes are additional vectors of Mayaro virus and yellow fever.
These diseases can have similar symptoms and can result in a variety of complex medical problems, including death. Because Ecuadorians are coming in frequent contact with mosquitoes, they are at high risk of developing one or more of these diseases in their lifetime. Fortunately, there is a lot of research into these viruses, their vectors, and their epidemiology in Ecuador. Researchers at the University of Florida recently published a synthesis paper, entitled “Endemic and Emerging Arboviruses of Mosquitoes in Ecuador” in a special Tropical Medicine issue of the Ecuadorian journal Practica Familiar Rural. The article covers the history of these diseases, vectors, viruses, transmission cycles, clinical presentation, epidemiology, and ongoing research on mosquito-borne arboviruses within the context of Ecuador.
“It can be really challenging for researchers and clinicians in Ecuador to stay up-to-date on the latest research findings” says Dr. Rachel Sippy, lead author on the paper. “The majority of the medical and research literature is published in English and usually is not accessible through paywalls”. The team hope that by providing an extensive review of the literature, in a local journal, in Spanish, they can help the scientific community in Ecuador and South America stay up-to-date on recent findings in this area of research. “Dissemination of information in local communities is one of our primary goals as researchers” says Dr. Sippy. “We host outreach events for the general public, but publishing hard data for the scientific community in the local language is another important part of that goal.”
RESUMEN SOBRE LAS BRECHAS EN LA INVESTIGACIÓN Y EL CONOCIMIENTO SOBRE LOS ARBOVIRUS TRANSMITIDOS POR MOSQUITOS EN ECUADOR
Los investigadores y médicos de Ecuador se enfrentan a un entorno desafiante: este país de biodiversidad es hogar de muchos portadores y vectores de enfermedades. En particular, los mosquitos en Ecuador portan y transmiten arbovirus (virus transmitidos por artrópodos). Este grupo incluye enfermedades como el dengue, chikungunya, virus Mayaro, fiebre amarilla y Zika, entre otras. Todos se propagan por la superposición de especies de mosquitos. Aedes aegypti y Aedes albopictus transmiten dengue, chikungunya, Zika, virus Mayaro y fiebre amarilla. Los mosquitos Haemagogus y Sabethes son vectores adicionales del virus Mayaro y la fiebre amarilla.
Estas enfermedades pueden tener síntomas similares y pueden resultar en una variedad de problemas médicos complejos, incluida la muerte. Debido a que los ecuatorianos entran en contacto frecuente con los mosquitos, corren un alto riesgo de desarrollar una o más de estas enfermedades en su vida. Afortunadamente, hay mucha investigación sobre estos virus, sus vectores y su epidemiología en Ecuador. Investigadores de la Universidad de Florida publicaron recientemente un artículo de síntesis, titulado “Arbovirus endémicos y emergentes de mosquitos en Ecuador” en un número especial de Medicina Tropical de la revista ecuatoriana Practica Familiar Rural. El artículo cubre la historia de estas enfermedades, vectores, virus, ciclos de transmisión, presentación clínica, epidemiología e investigación en curso sobre arbovirus transmitidos por mosquitos en el contexto de Ecuador.
“Puede ser realmente un desafío para los investigadores y los médicos en Ecuador mantenerse al día con los últimos hallazgos de la investigación”, dice la Dra. Rachel Sippy, autora principal del artículo. “La mayor parte de la literatura médica y de investigación se publica en inglés y, por lo general, no se puede acceder a ella mediante paywalls”. El equipo espera que al proporcionar una revisión extensa de la literatura, en una revista local, en español, puedan ayudar a la comunidad científica en Ecuador y Sudamérica a mantenerse actualizada sobre los hallazgos recientes en esta área de investigación. “La difusión de información en las comunidades locales es uno de nuestros principales objetivos como investigadores”, dice la Dra. Sippy. “Organizamos eventos de divulgación para el público en general, pero la publicación de datos concretos para la comunidad científica en el idioma local es otra parte importante de ese objetivo”.
ABSTRACT: Models predicting disease transmission are vital tools for long-term planning of malaria reduction efforts, particularly for mitigating impacts of climate change. We compared temperature-dependent malaria transmission models when mosquito life-history traits were estimated from a truncated portion of the lifespan (a common practice) versus traits measured across the full lifespan. We conducted an experiment on adult female Anopheles stephensi, the Asian urban malaria mosquito, to generate daily per capita values for mortality, egg production and biting rate at six constant temperatures. Both temperature and age significantly affected trait values. Further, we found quantitative and qualitative differences between temperature–trait relationships estimated from truncated data versus observed lifetime values. Incorporating these temperature–trait relationships into an expression governing the thermal suitability of transmission, relative R0(T), resulted in minor differences in the breadth of suitable temperatures for Plasmodium falciparum transmission between the two models constructed from only An. stephensi trait data. However, we found a substantial increase in thermal niche breadth compared with a previously published model consisting of trait data from multiple Anopheles mosquito species. Overall, this work highlights the importance of considering how mosquito trait values vary with mosquito age and mosquito species when generating temperature-based suitability predictions of transmission.
Research Statement: I am broadly interested in vector-borne diseases, public health vector control, and investigating the social and ecological factors that affect mosquito-borne disease transmission. My graduate research is focused on arthropod-borne viruses (arboviruses) transmitted by mosquitoes in Ecuador, such as dengue, chikungunya, and Zika viruses. I conduct spatial and statistical analyses on entomological and public health surveillance data, the results of which are shared with the Ministry of Health, Ecuador to inform decision making and guide future research.
Who is she? Cat Lippi is a fifth year PhD candidate in the Geography Department. Born in Louisiana, she has spent most of her life in Florida. She earned her B.S. in Wildlife Ecology and Conservation and M.F.A.S. in Fisheries and Aquatic Sciences at the University of Florida, before returning to UF to pursue her PhD in the Quantitative Disease Ecology & Conservation Lab (QDEC Lab) and has served as a Graduate Representative for the 2019/2020 academic year.
How did she get here?
Cat was born in Louisiana, but her family moved to Jacksonville, FL when she was 4 years old. As a child, she dreamed of becoming a wildlife veterinarian.
As a first step toward that goal, Cat pursued a B.S. in Wildlife Ecology and Conservation at the University of Florida. As an undergrad, Lippi worked in the Herpetology collection at the Florida Museum of Natural History and during the summer she worked at a small animal clinic in Jacksonville. While at the FLMNH, Cat researched the phylogeography of the eastern indigo snake in Florida – a federally protected species. Cat’s interests gradually shifted towards wildlife research. “I felt like I could make more of a difference in the world by applying research to solving conservation problems.”
After attaining her Bachelor’s degree, Cat took a job as a reptile zookeeper at St. Augustine Alligator Farm Zoological Park. After a (non-work related) accident that left her on crutches, she came to the realization that “It turns out you can’t work with gators and crocs when you’re on crutches,” and she took a job at the Jacksonville Zoo and Gardens working with marine invertebrates and stingrays (“The Stingwrangler”).
After working as a zookeeper, Cat eventually missed research, so she returned to UF to pursue a MFAS in Fisheries and Aquatic Sciences. Once she had completed her coursework for the Master’s, she nearly ran away with the circus (literally! She interviewed with Ringling Bros), but decided to take a job as a Museum Collections Assistant in the Division of Vertebrate Zoology at Yale Peabody Museum in New Haven CT, where she was able to work with both fish and herps (reptiles and amphibians). While in New Haven, she conducted her Master’s fieldwork in Long Island Sound on a National Oceanic and Atmospheric Administration (NOAA) project where she explored the role of predatory species on winter flounder, a commercially important fish species.
After completing her Master’s degree, Cat returned to St. Augustine, FL (fun fact- the oldest continuously occupied European settlement in North America) and went to work at UF’s Whitney Lab for Marine Biosciences in Marineland, FL as a lab tech in fish neurobiology and flow mechanics. After her time at Whitney Lab concluded, Cat noticed that most local science jobs required specialized statistical experience, typically centered on human health problems. Seeking to expand her quantitative skills, Cat decided to go back to school and study epidemiology and graduate level statistical analysis as she pursued a Graduate Certificate in Applied Biostatistics from the Department of Epidemiology and Biostatistics at the University of South Florida.
Once she was studying remotely at USF, she realized that specializing in public health opened a lot of doors to other jobs where she could make a positive impact in the local community. While completing her public health coursework, Cat also worked in Health Education Support at the Baker County Department of Health, as an Environmental Health Specialist at the St. Johns County Health Department, and as an Adjunct Professor of Biology at Flagler College in St. Augustine.
Cat had to fulfill a field requirement for her new public health graduate program, and most students would typically apply at a local health department. Cat, however, found a three month research opportunity as a Graduate Research Intern in Public Health Vector Control at the Anastasia Mosquito Control District in St. Augustine, allowing her to pursue a budding interest in infectious diseases. “I learned so much there in such a short amount of time!” says Cat. She was immediately hooked on mosquitoes, and the internship eventually led to an invitation to continue on a six month project. During her studies, Cat began to learn and understand the importance of arthropod-borne diseases in public health. Vector control and the study of mosquito-borne diseases was an almost perfect overlap with her ecology background and more recent training in epidemiology and public health, and she completed her graduate internship with a new focus on vector-borne infectious diseases.
When Cat earned her Graduate Certificate, she briefly considered staying on for a Master of Public Health at USF, but soon realized that working full time while completing another Master’s degree would actually take longer than just earning a PhD. After exploring different doctoral programs, Cat found a great match with Dr. Sadie Ryan at UF, and applied to join the Quantitative Disease Ecology & Conservation Lab. The research projects in QDEC were a perfect fit for Cat. She would be studying mosquito-borne disease systems in Ecuador, which was serendipitous (her husband is half Ecuadorian, and they make regular trips to visit family).
Cat’s path has been anything but linear – the things she’s done in life have been based on trying lots of things and seeing what works. Her advice, “Many students (especially undergrads) have anxiety about what they’re going to do with themselves – I would never discourage a student from working a job or getting experience to help them figure out where their place might be.”
What’s she been doing at UF?
Since joining the Department as a PhD student (and pursuing a PhD minor in Entomology), Cat has been incredibly prolific, taking courses, teaching courses, winning awards, authoring or coauthoring at least 17 papers, and serving as a Graduate Representative for the 2019/2020 academic year.
The single most influential course she’s taken was Dr. Blackburn’s Applications of GIS for Disease Ecology and Zoonosis. At the end of her fourth year as a PhD student, she regularly uses the concepts, principles, and techniques she learned in that class. The class helped make up for her lack of experience in Geography upon entering the graduate program, and helped frame her epidemiological knowledge in a geographic context. She still consults the coffee stained notes from the class on a regular basis.
All of this work has not gone unrewarded – Cat received the 2019 American Committee on Arthropod-borne Viruses (ACAV) Student Award and the 2019 Ryan Poehling Fellowship, UF Geography.
How has she been holding up during the pandemic?
In addition to working on research projects, Cat has been spending a lot of time outdoors and doing a lot birding. As part of the Alachua County Audubon Society June Challenge, Cat observed 99 different species of birds in the month of June within the county – one shy of her goal.
Just before the pandemic, Cat bought an historic home that was badly in need of renovation, which has not been going as quickly as she hoped – she’s looking forward to hosting parties, once that becomes a thing again. As if that wasn’t enough Cat has been teaching herself how to play a secondhand theremin, and has been running virtual social events for the Gainesville Roller Rebels – our local roller derby team – trying to stay connected and keep people engaged, even when they can’t skate together.
Research Statement: My research interests are in the application of GIS to understand vector-borne transmission. My past work has focused on range expansions of Ae. aegypti and Ae. albopictus, two mosquito vectors of dengue, chikungunya, and Zika virus. Moving forward, I plan to study spatial factors affecting vector distributions, insecticide resistance, and virus transmission in order to build spatial models of current and future arthropod-borne disease transmission.
How did she get here?
Growing up in Harvard, Illinois with high school teachers for parents, Stephanie was steeped in the value of education. Although Harvard is a small town (population of 9,447 at the 2010 census), it is remarkably cosmopolitan – hosting many international students through the AFS program which is committed to the idea that fostering international relationships fosters peace. Stephanie’s parents have hosted students from Spain, Norway, Thailand, and Hong Kong and, while in High School, Stephanie was able to spend a year abroad in Temuco, Chile.
Stephanie started a B.A. in Anthropology at the University of Illinois at Urbana-Champaign in Fall 2010. When she took an introductory course on the geography of developing countries, she was hooked and decided to add Geography as a second major. She liked using GIS and saw geography as a field that used both qualitative and quantitative methods to investigate an important and diverse array of questions. While an undergrad, she started studying socio-cultural anthropology, but became interested in physical anthropology when she worked in a human genetics lab that focused on Native American population genetics looking into the peopling of the Americas. She also began to study medical geography in a lab looking at West Nile Virus with GeoGator alumna Marilyn O’Hara. Combining her interests in genetics and geospatial science, Stephanie also spent a summer in the Genomics Research Laboratory designing a geodatabase that used genetics to determine the provenance of illegal elephant ivory. Her undergraduate thesis involved GIS and genetics – exploring the spatial relationships between different indigenous communities in Central and South America.
After completing her undergraduate studies, Stephanie took a year off school, and worked on mosquito control, as a laboratory technician in a medical entomology lab as a tech and did a 3 month GIS technician internship.
With some practical experience in hand, Stephanie was ready to move to Las Cruces, NM and enroll in a Master’s program at New Mexico State University. She was initially pursuing an interdisciplinary Master’s degree, but wound up earning a M.S. in Biology and a Master of Applied Geography on the strength of a single thesis, exploring the species distribution of Aedes aegypti mosquitoes in New Mexico. She was working with a species distribution model of data from the southern ¾ of the state – asking where are the mosquitoes and where might they be in different climate change scenarios. While pursuing her Master’s degree, Stephanie coauthored a paper looking at mosquito composition in different land cover types in Borneo based on land surface temperature.
Since the beginning of her undergrad, Stephanie has wanted to be a professor. She brings that passion to the (now virtual) classroom, teaching sections of Introduction to Medical Geography as well as the Introduction to Physical Geography Lab.
As part of her work with the CDC Southeastern Center of Excellence in Vector Borne Diseases, Stephanie has been able to get into the field, studying local scale variability of insecticide resistance in Aedes aegypti with the Orange County Mosquito Control District. This fieldwork has come to a halt with the COVID-19 pandemic, but she continues to work with data from Orange County, working on a local scale project studying mosquito abundance and climate, using data that has already been collected from sentinel chickens in Orange County.
Stephanie has also received the T.W. Miller Scholarship from the Florida Mosquito Control Association as well as a US Geospatial Intelligence Foundation Graduate Student for an essay exploring how mosquito borne disease is a threat to health and security.
How has she been holding up during the pandemic?
As an introvert, Stephanie is happy to not leave her house – it’s her favorite place. She has been okay with staying home as much as possible, spending time reading, cooking, and going for walks with her dogs.
We need a national tick strategy, UF Medical Geography researcher Dr. Claudia Ganser argued in a recent paper.
“Historically in the U.S., public health has focused more on mosquitoes versus ticks,” Ganser says. “A lot of the public health infrastructure of surveillance programs that is already in place focuses on mosquitoes rather than ticks,” Ganser says. “The idea behind this project was to take inventory of what we know, to gather what information exists in the regions that have ticks, and to identify the gaps in making things more uniform.”
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.
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.
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.
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.
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.
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.
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%.
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.
Associate Professor, Department of Geography, University of Florida
Thursday, January 16, 2020
2:50-3:50 PM (Period 8)
Turlington Hall Room 3018
University of Florida
All are welcome to attend.
Forecasting the impacts of climate change on vector-borne diseases (VBDs)—especially those under current public scrutiny and concern, such as malaria, dengue, chikungunya, and Zika—is a key component of global public health preparedness, and a key component of the ongoing issue of climate change preparedness. In this talk, I will showcase a strategy for applying ecophysiological models of temperature-dependent transmission to current and future climate models at large scales. I will demonstrate how our collaborative team have used these models to explore future scenarios for malaria, and for Aedes spp transmitted diseases, and how we can use mapping approaches as useful visualization tools, and how we tackle describing the multiple potential outcomes. I will also describe some local-scale, city and province level approaches to understanding vectorborne disease dynamics and management, and explore issues of how these two scales come together (or don’t) for decision making on the ground and in the boardroom.
Bio: Sadie J. Ryan is an Associate Professor of Medical Geography in the Department of Geography and in the Emerging Pathogens Institute (EPI) at the University of Florida, and PI of the Quantitative Disease Ecology and Conservation (QDEC) Lab group (www.sadieryan.net).
Ryan’s training is in Ecology and Evolutionary Biology (BA, Princeton), with an emphasis on conservation biology, quantitative ecology, and particularly, disease ecology. Ryan’s PhD work (UC Berkeley) centered on African buffalo spatial ecology in their savanna environment, in the context of an epidemic of Bovine Tuberculosis. Ryan’s postdoctoral work in Anthropological Science (Stanford, McGill), Ecology (NCEAS) and Geography (UCSB), launched her interdisciplinary work looking at the anthropogenic impacts of land use change, climate change, and conservation management goals in African parks landscapes, and the role of socioecological systems in disease transmission in Africa and Latin America.
This research continues today, investigating the multiscale issues of climate-health relationships in and on landscapes, and interactions with livelihoods, sustainability, parks management goals, the urban environment, and local perceptions. QDEC Lab is home to multiple projects in ecology at the human interface, spanning socioecological systems of vector borne and environmental disease ecology, climate-health modeling, insecticide resistance, and wildlife conservation, from Florida to the Old and New World tropics.