When the COVID-19 pandemic shut down international travel in 2020, Michigan State University researcher Eric Benbow faced a problem.
A $2.5 million research project designed to study an environmental pathogen in South America was suddenly on hold. With fieldwork canceled and uncertainty surrounding when travel might resume, Benbow and his collaborators needed a new plan.
That unexpected detour led to a surprising discovery — and new insights into a disease that has puzzled scientists for decades.
In a study published in Communications Medicine, an international team of researchers examined the environmental and human factors that influence the distribution of Buruli ulcer, a neglected tropical disease caused by the bacterium Mycobacterium ulcerans. The work helps explain how ecosystems, climate, land use and human activities interact to shape disease risk.
“People often think about infectious diseases in terms of person-to-person transmission,” said Benbow, professor in the Department of Entomology in the College Agriculture and Natural Resources and in the Department of Osteopathic Medical Specialties in the College of Osteopathic Medicine. “But this pathogen lives in the environment. To understand the disease, we have to understand the ecosystem.”
Buruli ulcer is most common in parts of West and Central Africa and can cause severe skin ulcers, scarring and disability. Yet despite decades of study, scientists still do not fully understand how people become infected.
“It’s been called the ‘mysterious disease’ for decades because no one really knew how it was transmitted,” Benbow said.
Using hundreds of environmental variables, researchers identified patterns linking disease occurrence to factors such as flooding, land disturbance, agriculture, invasive plant species and climate conditions.
The findings support a growing body of research showing that environmental change can influence where pathogens persist and where people are most likely to encounter them.
“We’ve been taking a One Health approach to this disease for more than 15 years,” Benbow said. “You can’t separate human health from environmental health.”
The study also builds on an unexpected discovery made during the pandemic.
Unable to travel to South America, Benbow’s team shifted its attention to the southeastern United States after uncovering an old study suggesting the pathogen might exist there. Using newer molecular tools, the researchers sampled aquatic habitats across the region and confirmed the bacterium’s presence.
“We found it,” Benbow said.
The researchers later found other areas in the U.S. that are favorable and, therefore, were able to expand the known environmental range of the pathogen. Combined with the study’s global modeling results, the findings suggest that suitable environmental conditions for Mycobacterium ulcerans may exist in more places than previously recognized, even where human cases of Buruli ulcer have not been reported.
That discovery aligned with the new global modeling work, which identified portions of the southeastern United States as environmentally suitable for the pathogen, despite no known locally acquired human cases of Buruli ulcer.
The question now is why.
“Why are people getting the disease in some places and not others?” Benbow said. “That’s one of the major questions we’re trying to answer.”
While the study focuses on Buruli ulcer, Benbow says the broader implications extend far beyond a single disease.
“We’re using Buruli ulcer as a model system,” he said. “The larger question is how environmental change influences disease risk.”
Researchers increasingly recognize that human health is connected to the health of ecosystems. Changes such as agricultural expansion, invasive species, urban growth, mining and shifting climate conditions can alter where pathogens persist, how they disperse and how people encounter them.
By identifying the environmental conditions associated with disease-causing organisms, scientists can better anticipate future risks, improve surveillance efforts and help public health officials focus resources in areas where disease emergence may be more likely.
“The goal isn’t just to understand where a disease is today,” Benbow said. “It’s to understand the conditions that allow it to emerge so we can be better prepared for what’s coming next. These pathogens don’t suddenly appear out of nowhere. Many are already part of the natural environment. The challenge is understanding what conditions allow them to become a threat. When we alter landscapes, we can sometimes wake sleeping giants.”
The study included researchers from Michigan State University, Mississippi State University, the University of Montpellier and several international institutions.
