April 25, 2019: New research by EPI and College of Liberal Arts and Sciences medical geographers offers Ecuadorian health officials a sneak preview of where mosquito-borne diseases may shift into the Andean mountain foothills as our planet’s climate warms into the midcentury.
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: detailed maps recently published in PLoS Neglected Tropical Diseases which offer a sneak preview of where mosquitoes are likely to be in a warmer future – and therefore, where diseases will follow.
The new work comes from UF’s Quantitative Disease Ecology and Conservation Lab, along with the Emerging Pathogens Institute and College of Liberal Arts and Sciences, and assesses the current and future geographic distribution of Ae. aegypti throughout Ecuador. The study was led by CLAS geography department doctoral candidate Cat Lippi. It 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 Sadie Ryan, also contributed to the project, as did EPI investigator 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. (See map above.) Aedes aegypti is important because it is a vector for several different mosquito-borne diseases, but it is also highly tied to urban areas due to its ability to reproduce in small quantities of standing water – a habit that places it in contact more frequently with people. The research team then used high-powered environmental and climate modeling to analyze how areas currently suitable for the mosquito may shift in the future as a result of climate change. See below, maps A and E show estimated 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 then 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.
Study results show that Ae. aegypti is likely to expand its 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, this mosquito’s range will contract in the eastern portion of the country’s Amazon basin.
Under the more extreme scenarios of climate change, mosquitoes may invade new locations more than 900 meters higher in elevation than current climatic conditions permit. This means that about 12,000 or more people living in the foothills of the Andes may be at future risk of exposure to mosquito-borne diseases.
“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 repellant, 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.”
Cowritten by Cat Lippi and DeLene Beeland. Photo of Aedes aegypti (top), courtesy of CDC/Prof. Frank Hadley Collins, Dir., Cntr. for Global Health and Infectious Diseases at the Univ. of Notre Dame/James Gathany; Maps courtesy of Lippi et al.
Read their science paper here.
Read Sadie Ryan’s EPI profile here.
Read Jason Blackburn's EPI profile here.
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