Virginia Tech mathematical biologist works with international team to analyze rise in dengue outbreaks

What weighs just 2.5 milligrams, yet is considered the deadliest animal in the world, causing an estimated 700,000 human deaths annually?

The mosquito.

A stealthy creature that can drink twice its weight in blood with each bite, the mosquito spreads diseases such as malaria, yellow fever, Zika, West Nile virus, and chikungunya.

But one particular mosquito-borne disease – dengue – has piqued the interest of Michael Robert, assistant professor in the Virginia Tech Department of Mathematics.

Dengue, also known as break-bone fever, is a viral infection most common in tropical and subtropical climates. The incidence of dengue has risen dramatically in recent years. According to the World Health Organization, a historical high of more than 6.5 million cases of dengue were recorded worldwide in 2023.

The rise of dengue cases in the Americas has been even more marked. After a record high of 4.6 million cases in 2023, there were more than 7 million cases reported in the Americas through the end of April 2024. Additionally, areas such as Puerto Rico, Brazil, and Peru all declared health emergencies from dengue in the early months of 2024.

Regions that hadn’t previously been affected by dengue – particularly those with more moderate climates – are seeing increased cases as well. In 2009, dengue reached Córdoba, the second-largest city in Argentina as well as other central provinces in the country for the first time. Since then, the central region has seen multiple large outbreaks.

As the spread of dengue grows exponentially each year, Robert and a team of Argentinian collaborators want to know why.

All-star team

To answer the question of what is causing the rise in dengue cases, Robert, an affiliated faculty member with Virginia Tech’s Center for Emerging, Zoonotic, and Arthropod-borne Pathogens and core faculty in the newly formed Center for Mathematics of Biosytems, is working with an international team of diverse experts. While he provides expertise in mathematical modeling, other colleagues bring knowledge in areas such as epidemiology, entomology, ecology, geospatial analyses, climate science, and public health.

“The goal is that we want to use an all-hands approach,” said Robert. “It’s a very interdisciplinary approach to studying this problem.”

Working directly with Robert are two of his graduate students from Virginia Commonwealth University along with four undergraduate students and a recent graduate from Virginia Tech. Meanwhile, Elizabet Estallo, an independent investigator at the Institute of Biological and Technological Research, National Scientific and Research Council of Argentina, National University of Córdoba, heads up the team in Argentina, which currently includes a graduate student, three other faculty members at the National University of Córdoba, and three technicians. The team also is working in partnership with the local health department as well as colleagues in nearby provinces.

Climate change and the rise of the mosquitoes?

One of the most significant factors associated with the growth in global dengue transmission is climate change, which has led to increased temperatures as well as more erratic patterns in rainfall and high levels of humidity.

“The mosquito’s entire life cycle is highly regulated by temperature, and so part of what’s happening is that the mosquito species is moving farther south of the equator and farther north of the equator,” said Robert. “Environmental conditions are becoming more suitable for the mosquito species in these places, and so it’s having an easier time getting established.”

In 2023, Robert and his collaborators published an article analyzing climate trends and their relationship to dengue incidence in Argentina. The study, which looked at climate data for a period of 60 years, illustrated trends between temperature and dengue cases – as regions got warmer, dengue outbreaks increased – while relationships with precipitation were also found. However, there was not enough data in the analysis to determine that these changes in climate were significant.

Better data, better models

Now, with the help of a three-year grant – the Burroughs Wellcome Fund Climate and Health Interdisciplinary Award – Robert and his team are focusing on building the infrastructure for collecting better data to be able to create better models for predicting dengue transmission. The first two years of the grant project are focused on data collection while analysis of that data will drive the final stage.

“As a mathematical biologist and mathematical modeler, my role in this is going to be working on building predictive models, but also building models that can help us better understand why transmission has been happening and what’s driving these outbreaks,” said Robert.

Citizen scientists

Data collection for this project is taking place in two locations in central Argentina: the urban, more densely populated city of Córdoba, and the smaller, suburban city of Villa Carlos Paz. Students at six high schools — five in Córdoba and one in Villa Carlos Paz — have been enlisted to collect mosquito data for the project using ovitraps, containers in which mosquitos lay their eggs but are unable to escape.

“Getting the high school students involved in this citizen science project is really important,” said Robert. “It’s not only an introduction to science and data collection, but it’s also giving them some agency in responding to the public health problem that’s happening, which is something that we don’t always get to do.”

During the collection period, which runs from roughly October to May, students take home an ovitrap each week to place around their homes before returning it for an empty container. While the ovitraps provide information about mosquito population, nearby meteorological stations collect hourly data on conditions such as temperature, precipitation, and humidity to offer a more complete picture.

According to Robert, “With this, we can do a more robust analysis to get a sense of how climate is impacting the mosquito population and, if there are dengue outbreaks in this time, how that climate is also related to the dengue cases.”

Early warning system

One goal of Robert’s research in Argentina is to create new predictive models – more specifically, an early warning system for dengue transmission that can be turned over to a public health or vector control department.

“The idea behind an early warning system is kind of like a weather forecast,” said Robert. “We look at relationships between things like climate and disease outbreaks and we can use that information to generate a warning basically that the climate conditions are favorable for an outbreak, so we should be on the lookout over this period of time.”

The impact

While Robert’s current project focuses on just two cities in Argentina, the goal is to expand to other areas in central Argentina. He hopes to get a better sense of how different types of climate zones are being impacted, as well as how the varying climates and environments are driving disease dynamics.

Robert also notes that what is happening in central Argentina could be an indicator of what is to come closer to home.

“We need to be paying more attention to what’s happening in other places, in part because we’re not necessarily going to be safe from these issues,” said Robert. “The climate in the region we are studying is not unlike the climate in some of the southern U.S. states. From this project, I think we can learn a lot about dengue fever and the relationship between climate and why it’s sort of creeping into temperate areas, and use that to get a head start in other places.”