GAINESVILLE – In the battle against vector borne disease, mosquito control using insecticides is an essential tool. But what happens when that tool starts to fail, and how do you know it? Insecticides are regularly used by public health agencies to reduce populations of blood-sucking mosquitoes. Effective control programs are important to public health because, in addition to posing a nuisance, mosquitoes can also spread diseases to humans. Insecticide resistance, where mosquitoes adapt to survive exposure to commonly-used chemicals, has become an increasingly pressing issue for many health agencies, undermining mosquito control efforts. New research by the Quantitative Disease Ecology and Conservation (QDEC) Lab Group at the University of Florida, the Center for Research on Health in Latin America (CISeAL) at Pontificia Universidad Católica del Ecuador (PUCE), the Institute for Global Health and Translational Science at SUNY Upstate Medical University, Escuela Superior Politécnica del Litoral (ESPOL), and the Universidad Técnica de Machala is the first attempt to investigate seasonal and geographic variations of mosquito insecticide resistance in southern coastal Ecuador, a region where mosquito control is key to stopping the spread of serious diseases like Zika and dengue fever. The study was funded by the U.S. Centers for Disease Control and Prevention (CDC). The team of researchers used both genetic screening and pesticide assays to evaluate insecticide resistance in mosquitoes collected in urban locations at different seasons. Differences in the resistance status of mosquitoes to the insecticides commonly used by the local health ministry were found both across collection seasons and across the four cities in the study area. Detected resistance to Malathion, deltamethrin, and alpha-cypermethrin was particularly high in the port city of Machala, which has a long history of dengue outbreaks and insecticide use. Information on insecticide resistance status, patterns, and timing will help local public health professionals design sustainable mosquito control programs that will continue to be effective in the fight against disease.

Read Seasonal and geographic variation in insecticide resistance in Aedes aegypti in southern Ecuador, at PLoS Neglected Tropical Diseases.

La Resistencia a los Insecticidas Amenaza el Control de las Enfermedades Transmitidas por Mosquitos en Ecuador

GAINESVILLE – En la batalla contra las enfermedades transmitidas por vectores, el uso de insecticidas para el control de mosquito es una herramienta esencial. Pero ¿qué sucede cuando esa herramienta comienza a fallar y cómo lo sabe? Las agencias de salud pública utilizan regularmente los insecticidas para reducir las poblaciones de mosquitos que chupan la sangre. Los programas de control efectivos son importantes para la salud pública porque, además de ser una molestia, los mosquitos también pueden transmitir enfermedades a los humanos. La resistencia hacia los insecticidas, donde los mosquitos se adaptan para sobrevivir a la exposición a sustancias químicas de uso común, se ha convertido en un problema cada vez más urgente para muchas agencias de salud, desfavoreciendo los esfuerzos de control de mosquitos. Una nueva investigación realizada por el Grupo de Laboratorios de Ecología y Conservación de Enfermedades Cuantitativas (QDEC) en la Universidad de Florida, el Centro de Investigación para la Salud en América Latina (CISeAL) en la Pontificia Universidad Católica del Ecuador (PUCE), el Instituto de Salud Global y la Ciencia Traslacional en la Universidad Médica del Estado de SUNY, la Escuela Superior Politécnica del Litoral (ESPOL), y la Universidad Técnica de Machala es el primer intento en investigar las variaciones estacionales y geográficas sobre resistencia a insecticidas en mosquitos en la costa sur de Ecuador, una región donde el control de mosquitos es clave para detener la propagación de enfermedades graves como el Zika y el Dengue. El estudio fue financiado por los Centros para el Control y la Prevención de Enfermedades (CCPEEU). El equipo de investigación usó tanto análisis genético como los ensayos de pesticidas para evaluar la resistencia a insecticidas en los mosquitos recolectados en áreas urbanas, en diferentes estaciones. Diferencias en el estado de resistencia en mosquitos a los insecticidas comúnmente utilizados por el ministerio de salud local, se encontraron tanto en las diferentes temporadas de recolección, como en las cuatro ciudades dentro del área de estudio. La resistencia detectada al malatión, la deltametrina, y la alfa-cipermetrina fue particularmente alta en la ciudad portuaria de Machala, que tiene una larga historia de brotes de dengue y uso de insecticidas. La información sobre el estado de resistencia hacia insecticidas, los patrones y el tiempo ayudará a los profesionales de la salud pública local a diseñar programas sostenibles de control de mosquitos que continuarán siendo eficaces en la lucha contra la enfermedad.

Lee Seasonal and geographic variation in insecticide resistance in Aedes aegypti in southern Ecuador, en PLoS Neglected Tropical Diseases.

 

Media contact: Mike Ryan Simonovich

Image credit: CDC/ Prof. Frank Hadley Collins, Dir., Cntr. for Global Health and Infectious Diseases, Univ. of Notre Dame/James Gathany

GAINESVILLE – Blood sucking insects such as the Yellow fever mosquito, Aedes aegypti, are more than just a nuisance in Ecuador, they also spread diseases such as dengue fever, chikungunya and Zika. A warming world means that public health officials must decide where to direct surveillance and mosquito control efforts not only today, but also decades down the road given dramatic shifts in mosquito habitat that will take place thanks to climate change.

Ecuadorian agencies now have a powerful helping hand: a recent paper in PLoS Neglected Tropical Diseases provides detailed maps forecasting where mosquitoes – and diseases – are likely to be in a warmer future.

The new work from the University of Florida’s Quantitative Disease Ecology & Conservation Lab Group (QDEC Lab) and the Emerging Pathogens Institute assesses the current and future geographic distribution of Ae. aegypti throughout Ecuador. The study was led by PhD Candidate Ms. Cat Lippi and is the result of a long-term collaboration with SUNY Upstate Medical University and the Ecuadorian Ministry of Health. Lippi’s committee chair, EPI researcher and QDEC founder Dr. Sadie Ryan, also contributed to the project, as did EPI investigator Dr. Jason Blackburn.

The research team repurposed historic larval mosquito surveillance data collected by the Ministry of Health between 2000 and 2012 in Ecuadorian households to predict where Ae. aegypti may occur in areas that have not yet been surveyed. Aedes aegypti mosquitoes are important because they are a vector for several different mosquito-borne diseases and are able to reproduce in small quantities of standing water, making them common in urban settings. The research team used environmental and climate modeling to analyze how areas currently suitable for the mosquito may shift in the future as a result of climate change.

Maps A and E show mosquito distribution today while maps B-D and F-H show where mosquitoes can be predicted in the future given different climate change scenarios.

“We wanted to show the Ministry of Health in Ecuador where disease-carrying mosquitoes might occur in the future,” Lippi says. By analyzing the environmental and climactic characteristics associated with where mosquitoes occur in Ecuador today, the team extrapolated where mosquitoes may occur in 2050 under a range of climate change scenarios and used the presence of these mosquitoes as a proxy for where disease would occur.

The models show that Ae. aegypti are likely to expand their range into regions of transitional elevation along the Andes mountain range by midcentury. The expanded habitat includes the portion of mountainous area where valley floors give way to a mountain’s lower slopes. The higher reaches of the Andes famed peaks are expected to remain protected pockets that will still be too cool, even with extreme warming, for Ae. aegypti to survive. At the same time, changing climate will reduce the mosquito’s range in the eastern portion of the country’s Amazon.

“When there is a population that has never been exposed to pathogens like dengue or Zika, they don’t have any immunity, and that population will be vastly more susceptible to an acute outbreak,” Lippi says. “There are thousands of Ecuadorians who will be exposed to mosquitoes in the future who have never had to deal with them before.”

The team will share their results with the Ecuadorian Ministry of Health, which will use the data to prepare for the future. Previous work through the team’s collaboration with Ecuador’s Ministry of Health showed that local knowledge and attitudes are significantly associated with the risk of Ae. aegypti mosquitoes in households in Ecuador, although effects on actual dengue fever risk are less clear. Mosquito-borne diseases pose a serious threat to public health throughout Ecuador and Latin America, where dengue alone accounts for an estimated 16 million infections occurring in the Americas each year.

“Our work gives their health department good forewarning of where to focus their preparations to prevent future outbreaks, and this will help them to conserve limited resources,” Lippi says. Preparations may include educational campaigns on using insect repellent, and window and door screens, as well as how to safely store household water in covered containers. The government can also coordinate spraying efforts to reduce mosquito larvae in the environment.

“Of course we expect to see changes in habitat and species’ ranges due to future climate change,” Lippi says. “But what this study addresses is the question of where those changes will occur, and how severe those changes may be, all within the context of disease risk to people.”

Un nuevo estudio de la Universidad de Florida (Estados Unidos) sugiere que los mosquitos que transmiten enfermedades podrían infectar a poblaciones humanas en Los Andes ecuatorianos debido al cambio climático

Comunidades en Latino América tienen el desafío de reducir la exposición a mosquitos que transmiten enfermedades, como el Aedes aegypti. En Ecuador, este mosquito es más que una molestia. El Aedes aegypti trasmite víruses que causan enfermedades de alta consideración para la salud pública incluyendo dengue, chikungunya y Zika. Dónde el Ministerio de Salud Publica (MSP) podría enfocar los esfuerzos de vigilancia y control de estos mosquitos, hoy y en el futuro, tomando en cuenta el cambio climático?

Un nuevo estudio del grupo, Ecología de Enfermedades y Conservación Cuantitativa (QDEC), de la Universidad de Florida, analiza la distribución geográfica del Aedes aegypti a través de todo Ecuador. El proyecto fue dirigido por Cat Lippi, estudiante de PhD de QDEC, y es el resultado de una colaboración a largo plazo con la Universidad del Estado de New York y Universidad Médica de “Upstate” (SUNY UPSTATE) y el MSP del Ecuador. El equipo de investigadores usó datos históricos de vigilancia de mosquitos recolectados por el MSP para predecir lugares donde Aedes aegypti podría estar presente. Áreas que no se ha inspeccionado de una manera activa y áreas donde podría estar presente en el futuro bajo condiciones de cambio climático. Modelos de “nicho ecológico” fueron creados usando información sobre lugares con la presencia actual del moquito y con variables básicos del ambiente. Los modelos fueron desarrollados usando condiciones climatológicas actuales y futuras, hasta el año 2050.

Este estudio muestra que lugares con elevaciones intermedias a lo largo de Los Andes pueden convertirse en zonas mas asequibles para la presencia de Aedes aegypti en el año 2050. Este descubrimiento sugiere que la población que actualmente viven en estas zonas de transición puede correr el riesgo, en el futuro, de ser expuesto a enfermedades transmitidas por mosquitos, como resultado de cambio climático. Los autores reportan que aumentará la población con riesgo de exposición por más de 12,000 personas bajo los escenarios extremos de cambio climático. Al mismo tiempo, los investigadores identificaron áreas que pueden ser menos propicias para los mosquitos, como la cuenca de la Amazonia.

Actualmente, la mayor parte de las personas que viven en Los Andes están protegidos por las enfermedades transmitidos por mosquitos debido a las altas elevaciones, lo que produce un ambiente frio y no apto para los moquitos. En situaciones extremas de cambio climático, los mosquitos pueden invadir nuevas lugares con elevación de 900 metros más alto que los lugares en actuales condiciones climatológicas. “Las personas que vivan en esta zona de expansión de enfermedades pueden ser más susceptibles a futuros brotes de enfermedades debido a varios factores, incluyendo falta de inmunidad debido a exposición previa al patógeno y falta de conocimiento y costumbres asociados con la prevención de mosquitos y costumbres de protección personal, como el uso de repelente,” indica Lippi. Estudios previos en colaboración con el MSP del Ecuador mostraron que el conocimiento y actitudes de las poblaciones locales están asociados con el riesgo de la presencia de Aedes aegypti en hogares en Machala. Se recomienda estudios en estos nuevas áreas de futuro riesgo.

Las enfermedades transmitidas por mosquitos son una amenaza para la salud pública en toda Latinoamérica, donde dengue causa aproximadamente 16 millones de infecciones anualmente. Estudios como éstos enfatizan la importancia de incorporar la ciencia de “Geografía de la salud” dentro de los estándares de la práctica de la educación pública, proveyendo información más precisa a las agencias de salud pública para mejorar el uso de escasos recursos para el de control de estas enfermedades y para desarrollar intervenciones de control vectorial y de educación pública en lugares específicos.

Media contact: Mike Ryan Simonovich

RYANTemperature drives Zika virus transmission: evidence from empirical and mathematical models

Blanka Tesla, Leah R. Demakovsky, Erin A. Mordecai, Sadie J. Ryan, Matthew H. Bonds, Calistus N. Ngonghala, Melinda A. Brindley, Courtney C. Murdock

Article first published online: 15 AUG 2018 Proceedings of the Royal Society B

DOI: 10.1098/rspb.2018.0795

ABSTRACT: Temperature is a strong driver of vector-borne disease transmission. Yet, for emerging arboviruses we lack fundamental knowledge on the relationship between transmission and temperature. Current models rely on the untested assumption that Zika virus responds similarly to dengue virus, potentially limiting our ability to accurately predict the spread of Zika. We conducted experiments to estimate the thermal performance of Zika virus (ZIKV) in field-derived Aedes aegypti across eight constant temperatures. We observed strong, unimodal effects of temperature on vector competence, extrinsic incubation period and mosquito survival. We used thermal responses of these traits to update an existing temperature-dependent model to infer temperature effects on ZIKV transmission. ZIKV transmission was optimized at 29°C, and had a thermal range of 22.7°C–34.7°C. Thus, as temperatures move towards the predicted thermal optimum (29°C) owing to climate change, urbanization or seasonality, Zika could expand north and into longer seasons. By contrast, areas that are near the thermal optimum were predicted to experience a decrease in overall environmental suitability. We also demonstrate that the predicted thermal minimum for Zika transmission is 5°C warmer than that of dengue, and current global estimates on the environmental suitability for Zika are greatly over-predicting its possible range.

Read the full publication at Proceedings of the Royal Society B

 

 

 

 

 

Image courtesy of Proceedings of the Royal Society B. Months of transmission suitability in the Americas of dengue (left) and Zika (right).

GAINESVILLE, FL – A University of Florida Medical Geography researcher recently participated in a study that found that current estimates of Zika virus transmission vastly over predict its possible range. Temperature is a major driver of vector-borne disease transmission, but current transmission models rely on untested assumptions about life history of Zika infected Aedes aegypti mosquitoes. Previous models of Zika transmission were based on similarities between Zika and dengue fever.

The study, led by Dr. Courtney Murdock from the University of Georgia, examined the influence of temperature on Zika transmission in lab-reared Aedes mosquitoes at eight different constant temperatures. Zika transmits optimally at a temperature similar to dengue, but the lowest possible transmission temperature of Zika is 5 degrees centigrade warmer than dengue. As global average temperatures increase under climate change the range of Zika will expand north and into longer transmission seasons, but some areas that are currently suitable for Zika transmission will no longer support transmission.

UF Medical Geography professor Dr. Sadie Ryan used the temperature relationships to make updated models and maps, which she compared with previous transmission models. “These maps show that the predicted area for year round risk of Zika transmission is over 6 million square kilometers smaller than previous models would predict,” said Ryan. “This shows that Zika is not dengue and we need to have specific transmission models for specific diseases.”

The findings have been published in a paper titled Temperature drives Zika virus transmission: evidence from empirical and mathematical models in Proceedings of the Royal Society B.

The study was part of a collaboration between UF’s Dr. Sadie Ryan and Dr. Calistus Ngonghala, the CDC Southeastern Center of Excellence in Vector Borne Diseases, the University of Georgia, as well as investigators from Stanford University and Harvard Medical School.

LIPPI, RYANNonlinear and delayed impacts of climate on dengue risk in Barbados: A modelling study

Rachel Lowe, Antonio Gasparrini, Cédric J. Van Meerbeeck, Catherine A. Lippi, Roché Mahon, Adrian R. Trotman, Leslie Rollock, Avery Q. J. Hinds, Sadie J. Ryan, Anna M. Stewart-Ibarra

Article first published online: 17 JUL 2018 PLOS Medicine

DOI: 10.1371/journal.pmed.1002613

ABSTRACT:

Background
Over the last 5 years (2013–2017), the Caribbean region has faced an unprecedented crisis of co-occurring epidemics of febrile illness due to arboviruses transmitted by the Aedes sp. mosquito (dengue, chikungunya, and Zika). Since 2013, the Caribbean island of Barbados has experienced 3 dengue outbreaks, 1 chikungunya outbreak, and 1 Zika fever outbreak. Prior studies have demonstrated that climate variability influences arbovirus transmission and vector population dynamics in the region, indicating the potential to develop public health interventions using climate information. The aim of this study is to quantify the nonlinear and delayed effects of climate indicators, such as drought and extreme rainfall, on dengue risk in Barbados from 1999 to 2016.

Methods and findings
Distributed lag nonlinear models (DLNMs) coupled with a hierarchal mixed-model framework were used to understand the exposure–lag–response association between dengue relative risk and key climate indicators, including the standardised precipitation index (SPI) and minimum temperature (Tmin). The model parameters were estimated in a Bayesian framework to produce probabilistic predictions of exceeding an island-specific outbreak threshold. The ability of the model to successfully detect outbreaks was assessed and compared to a baseline model, representative of standard dengue surveillance practice. Drought conditions were found to positively influence dengue relative risk at long lead times of up to 5 months, while excess rainfall increased the risk at shorter lead times between 1 and 2 months. The SPI averaged over a 6-month period (SPI-6), designed to monitor drought and extreme rainfall, better explained variations in dengue risk than monthly precipitation data measured in millimetres. Tmin was found to be a better predictor than mean and maximum temperature. Furthermore, including bidimensional exposure–lag–response functions of these indicators—rather than linear effects for individual lags—more appropriately described the climate–disease associations than traditional modelling approaches. In prediction mode, the model was successfully able to distinguish outbreaks from nonoutbreaks for most years, with an overall proportion of correct predictions (hits and correct rejections) of 86% (81%:91%) compared with 64% (58%:71%) for the baseline model. The ability of the model to predict dengue outbreaks in recent years was complicated by the lack of data on the emergence of new arboviruses, including chikungunya and Zika.

Conclusion
We present a modelling approach to infer the risk of dengue outbreaks given the cumulative effect of climate variations in the months leading up to an outbreak. By combining the dengue prediction model with climate indicators, which are routinely monitored and forecasted by the Regional Climate Centre (RCC) at the Caribbean Institute for Meteorology and Hydrology (CIMH), probabilistic dengue outlooks could be included in the Caribbean Health-Climatic Bulletin, issued on a quarterly basis to provide climate-smart decision-making guidance for Caribbean health practitioners. This flexible modelling approach could be extended to model the risk of dengue and other arboviruses in the Caribbean region.

Read the full publication at PLOS Medicine

 

 

 

 

 

Image credit: Ms. Catherine Lippi. This study was conducted with epidemiological data collected in Barbados, an island located in the Caribbean (left). Population in Barbados (middle) and elevation on the island (right) are shown, as well as the location of the two meteorological stations that provided climate data for the study.

GAINESVILLE, FL – Medical Geography researchers from the University of Florida recently participated in a study that successfully predicted dengue fever outbreaks on the Caribbean island of Barbados, using climate data. This paper is part of a special issue of PLOS MEDICINE, focusing on the impacts of climate change on health, and is a result of an unprecedented collaborative project, funded by USAID to address climate driven health impacts in the Caribbean.

The study, led by Dr. Rachel Lowe from the London School of Hygiene and Tropical Medicine, tested whether dengue outbreaks in the Caribbean island of Barbados could be predicted using weather station data for temperature and a precipitation index (Standardized Precipitation Index- SPI) used to monitor drought and extreme rainfall. Using data from June 1999 to May 2016, researchers found that the statistical model was able to successfully predict months with dengue outbreaks versus non-outbreaks in most years.
Dengue fever is spread by Aedes sp. mosquitos and infects over 350 million people each year, resulting in 25,000 deaths globally and costing households, governments, and businesses over $45 million annually. In recent decades, the disease has emerged as a major public health threat, and as many as 2 in 5 people globally are at risk of contracting dengue fever.

UF Medical Geography professor Dr. Sadie Ryan and doctoral student Ms. Catherine Lippi collaborated on models that explored the delayed effect of climate indicators like extreme rainfall and drought on future outbreaks of dengue fever on the Caribbean island.
“This study highlights the importance of keeping long term records of climate and health data so that we can learn about how a changing climate will impact our health and well-being in the future,” said Dr. Ryan.
The model found a sharp increase in disease transmission one to two months after extreme rainfall events, but a surprising result of the model was an increase in infections four to five months after a drought event. Lippi explained “During droughts, people store water in containers near their homes,” she said, “which creates the perfect habitat for Aedes mosquitos.” Senior author, Dr Stewart-Ibarra, from SUNY Upstate Medical University said she and others working on the project had heard from locals that this was a recurring trend but it wasn’t until they studied the data that they found it to be true. “Barbados is a water-scarce country. During periods of drought, people have to store water.”

The findings have been published in a paper titled Nonlinear and delayed impacts of climate on dengue risk in Barbados: A modelling study in PLOS Medicine.

The study was part of a collaboration between UF and the Caribbean Agency for Public Health, the Pan American Health Organization, the Caribbean Institute for Meteorology and Hydrology, as well as investigators from the London School of Hygiene and Tropical Medicine, SUNY Upstate Medical University, and the Escuela Superior Politecnica del Litoral of Ecuador.

 

Aedes control – image courtesy Mr. Dany Krom

GAINESVILLE, FL – New research co-authored by UF Geography’s Dr. Sadie Ryan and Ms. Cat Lippi sheds light on the climate suitability for Aedes aegypti and Aedes albopictus mosquitos and transmission rates of Zika, chikungunya, and dengue fever.

The study, published in PLOS Neglected Tropical Diseases compares new data driven models of Zika, chikungunya, and dengue fever transmission to real world measurements of human infections caused by bites from Aedes aegypti and Ae. Albopictus mosquitoes. These models confirm that temperature is the single most important factor for predicting the rate and geographic spread of epidemics of these mosquito-borne diseases. Temperature influences transmissibility in many ways – affecting the lifespan of an individual mosquito, and determining biting frequency and the reproductive rate of the virus within the mosquito.

The collaborative research team includes experts in epidemiology, public health, ecology, mathematical modeling, and geography, and was funded by a grant from the National Science Foundation’s Ecology and Evolution of Infectious Disease program (NSF-DEB 1518681).