In 2003, while on a research trip in Ecuador, Peter Larsen fell deathly ill. He was bedridden for days with a crushing fever, severe headache and joint pain, and exhaustion. For over two decades, he suspected he’d contracted dengue—often called "breakbone fever" because of the severity of its symptoms—but he didn’t know for sure until he began preparing for his most recent expedition to Malaysia.

"I had my antibodies checked, and the test confirmed I’d been exposed to dengue," says Larsen, an associate professor in the University of Minnesota (UMN) College of Veterinary Medicine (CVM). But contracting dengue no longer requires a trip to Ecuador or another far-flung place. 

Larsen’s experience is part of a staggering global trend. In the last 20 years, dengue cases have skyrocketed nearly tenfold, with the World Health Organization estimating that up to 400 million people are infected annually. Today, almost half of the world's population lives in areas at risk for the disease, as warming temperatures and rapid urbanization allow mosquitoes to push into regions that were once too temperate to support them.

“In the U.S., we’re starting to see it pop up in Florida and South Texas,” Larsen notes. And the implications are dire: “If you get dengue once, it’s severe. If you get it a second time, with a different serotype, it can be fatal."

The growing risks underscore why Larsen and a team of UMN researchers and graduate students from the Universiti of Malaysia, Sarawak recently spent three weeks trekking through the intense humidity of Borneo. The UMN researchers included Jon Oliver from the School of Public Health, along with wildlife epidemiologist Kendra Phelps, postdoctoral researcher Evan Kipp, and PhD student Lexi Frank—all members of Larsen’s lab at CVM. They were there to study the virus, with the ultimate aim of getting ahead of it.

It is a mission where the transmission of expertise is just as vital as tracking the transmission of the virus, ensuring that while dengue moves through the forest and around the globe, the skills to combat it are being passed to a new generation of researchers in both hemispheres.

Into the living lab

The team’s mission, funded by the UMN Center for Global Health and Social Responsibility, took them to the Sarawak state of Malaysian Borneo. To reach the primary research sites in Bako National Park, the team had to navigate the South China Sea by boat, eventually jumping into the surf at low tide to haul crates of sensitive equipment onto the beach.

"When you get into the forests there, you feel like you’re walking back into the Jurassic," Larsen says. "The sounds, the scale, the biodiversity—it all feels ancient. You feel very small because it’s this incredibly old, diverse, rich ecosystem—the mammals, birds, plants, insects, all of it."

Within that biodiversity lies a puzzle. Dengue is expanding its footprint due to climate change and increased urbanization. To stop it, scientists need to know where it hides and how it spreads when it’s not infecting humans.

Tracing the viral trail

While public health efforts often focus on the "urban cycle" of dengue—where the virus moves between people and mosquitoes in populated areas—the UMN team is looking deeper into the forest. They are investigating the "sylvatic cycle," the hidden transmission of the virus among wildlife that can act as a permanent reservoir for the disease.

To do this, they leverage the mosquito’s own biology. Instead of the difficult and invasive process of trapping and testing hundreds of individual birds or mammals, the team treats blood-fed mosquitoes as "living syringes." Using a technique pioneered in Larsen’s lab, the team collects blood-fed mosquitoes—insects that have just finished a meal. By sequencing the DNA of that blood, the researchers can identify exactly what animal the mosquito bit—whether it was a monkey, a bat, or a squirrel—effectively using the mosquito to sample the forest’s biodiversity for them.

"These methods help us identify those animal reservoirs," Larsen explains. "If we can go to a biodiversity hotspot like Borneo and identify which animals are involved in the transmission cycle, we can build predictive models. It helps us understand when the next large outbreak might happen, whether that's in Malaysia or the southern United States."

"What we're looking into now is how can we make best use of this technology to identify pathogens," says Faisal Anwarali Khan, UNIMAS researcher and dean of the Faculty of Resource Science and Technology. "It gives us so much more insight into the [animals] that we need to be concerned about... that potentially this pathogen can spread from or to."

Knowledge without borders

The expedition is the latest chapter in a nearly two-decade collaboration between Larsen and Khan, who first met as graduate students at Texas Tech University.

Today, after five research trips from the U.S to Malaysia, that friendship has blossomed into a full-circle training program that has opened up opportunities for both teams. Khan recalls when Larsen first introduced the new sequencing technology: "It was, I could say, a turning point, whereby we changed the whole direction of the lab." 

On this trip, the UMN team trained 12 UNIMAS students in the high-tech field of genomics used for mosquito identification and blood-meal analysis. The UNIMAS students, in turn, taught Larsen’s team new things about working effectively in the challenging environment—"things you could never know unless you’re living and working there day in and day out.”

"It’s about sustained engagement," Larsen says. He recalls meeting a UNIMAS student from a 2019 expedition, also funded by the Center for Global Health and Social Responsibility, who told him the training was life-changing. "He was able to leverage those skills for his dissertation and get jobs he wouldn't have been competitive for otherwise. It’s helping foster new life trajectories, and it’s bringing that knowledge into new realms."

One Health and global interconnection

For the UMN PhD students and postdocs on these trips, the experience helps deepen their data collection skills. But perhaps more importantly, it teaches them about the grueling, rewarding reality of international science.

"Our students are learning the logistics—how to pack for every 'what if,' how to teach in field conditions, and how to work with international collaborators," Larsen says. "That perspective is critical. You can’t understand global health until you’ve stood in it."

This boots-on-the-ground training is the lived reality of "One Health"—a framework that recognizes the health of people is inextricably linked to the health of animals and our shared environment.

"We saw this with the COVID-19 pandemic—how fast a virus can expand globally," says Larsen. "We’re no longer an isolated world. We are connected in ways we weren't even a few decades ago."

To Khan, the partnership is a vital exchange that empowers his students to safeguard both local and global health by unlocking the secrets of their own backyard. 

"We are very fortunate to work with the University of Minnesota," Khan says. "We really look forward to what’s next."

Scaling the impact

The Borneo expedition serves as the seed for two major initiatives that will continue to bridge the gap between Minnesota and Malaysia, between the classroom and the frontlines of global health, and between a history of reacting to outbreaks and a future of proactively preventing them.

First, the research and partnerships established in Sarawak will become a cornerstone of the UMN College of Veterinary Medicine’s new One Health minor. Those students will participate in a study abroad program on Langkawi Island, Malaysia, planned for an initial cohort in 2027. The program will allow more UMN students to witness biodiversity firsthand and work alongside international collaborators, developing the next generation of disease detectives.

On the research front, the team hopes that the data gathered this year will enable them to secure a major grant from the National Institutes of Health—comparing the transmission dynamics in Borneo to those emerging in the southern United States, with the ultimate goal of building a global early-warning system.

For Larsen, what began as a fever in Ecuador decades ago has evolved into a career-long mission to ensure the next generation of researchers is never caught off guard. By fostering these international ties and training students to look deep into the forest, the UMN team is making sure that as the world gets smaller, our ability to protect it grows larger.