Animals of all kinds mix and mingle in underground burrows, offering troubling opportunities for diseases to jump species.
In theory, it would take just one of these monkeys to bring Paris to a standstill. Or New York City. Or, for that matter, Belgium, thought Belgian ecologist Cédric Vermeulen as he watched recent video footage of patas monkeys, vervet monkeys, and a host of other animals navigating the entrances to aardvark burrows in Senegal’s Niokolo-Koba National Park.
“It was incredible how many species were coming inside, outside, and around the burrow,” Vermeulen says. Predators and prey were practically rubbing shoulders as they shuttled in and out of the burrows; warthogs, guinea fowl, leopards, partridges, pythons, porcupines, honey badgers, and baboons all made appearances. But what really caught Vermeulen’s attention in the footage he had acquired from remote cameras was the sight of bats and monkeys using the same burrow. Certain bat species are reservoirs for well-documented zoonoses — diseases that jump from animals to humans. Given the close relationship between monkeys and people, the overlap with bats raises the possibility that aardvark burrows are overlooked epicenters of pathogens spilling over from the wild to the human world.
Vermeulen is a professor at Belgium’s University of Liège, but he grew up in the Democratic Republic of the Congo and has spent years researching forest habitats in Cameroon, Gabon, and elsewhere in West Africa. To him, the number of animals visiting the burrow on a daily basis was astonishing. With the Covid-19 pandemic scarcely over, seeing so many species in such close contact also raised the specter of something sinister: the possibility that these burrows, and others like them, are incubators of disease.
At 3,525 square miles, Senegal’s Niokolo-Koba National Park is roughly the size of the Island of Hawaii. The park, listed as a World Heritage Site in Danger by UNESCO, is a biodiversity hotspot with expansive wetlands, savanna, and woodland ecosystems that attract ecotourists and researchers alike. Aardvarks are one of the most common burrowers in the region, and during the dry season of 2023 and 2024, Vermeulen and four graduate students set up cameras to monitor 105 entrances to 92 different burrows.
That animals are borrowing each other’s burrows is nothing new. In the park’s scorching savanna, where temperatures can reach 118 degrees Fahrenheit (48 degrees Celsius), some animals will seek shelter underground wherever they can find it. Aardvark burrows are also havens for insects, so some animals, including primates, are likely lured in by the small packages of protein they can find lurking in the darkness.
Though earlier research has shown that in arid climates aardvark burrows are regularly visited by various mammals, birds, and reptiles, scientists in general have spent little time studying how animals mingle in underground habitats. And as Vermeulen says, some visitor pairings are more worrisome than others. One of the species spotted swooping into Niokolo-Koba park’s aardvark burrows, for instance, was the large-eared slit-faced bat (Nycteris macrotis), which is a known carrier of coronaviruses that can infect both primates and humans.
Scientists have known for decades that bats are natural hosts for common viruses, including rabies, measles, mumps, and canine distemper. But over the past 25 years, bats have caught the attention of epidemiologists for carrying emerging viruses like Nipah, Marburg, and many coronaviruses, which can all cause severe infectious disease. Ebola is a formidable virus that likely moved from bats to primates to humans. The problem is not the bats themselves, which are invaluable to ecosystems, but the chain of infection they set off: A monkey may eat an infected bat and then itself end up as a bush meat meal for a person. Or, a fruit-eating bat may contaminate a mango, which is then picked up and eaten by a person.
Though we don’t typically think of monkeys as burrow dwellers, they do venture up to 6 feet inside, Vermeulen says. “And after that they go to the tourist camp or into the fields to eat human crops.” The park-run tourist camp, Niokolodge, is within 4 miles of the burrows studied, offering an opportunity for pathogens to hop from bats, monkeys, or other infected animals to people.
Alaina MacDonald is a veterinarian and doctoral candidate studying epidemiology under the One Health perspective at the University of Guelph in Ontario. One Health is a global scientific initiative that takes a broad view on health, exploring how humans, animals, ecosystems, and diseases are all interconnected. MacDonald says mixed-species mingling spots, such as aardvark burrows, are something that disease researchers should be paying more attention to.
Vermeulen’s analysis of animal interactions in Niokolo-Koba park’s aardvark burrows, recently published in 2025, also raises questions that need deeper examination, says MacDonald. For instance, does the combination of animals mingling in the burrows change depending on the season? “It probably does between the rain and the dry seasons,” MacDonald says. But “what does that tell us about risk and monitoring?”
With enough ecological knowledge, she says, it could become easier to surveil emergent diseases and the animals that carry them, and to find ways to prevent them from spilling over into human populations. “It’s really challenging but so important to understand the bigger picture,” MacDonald says.
Already, Vermeulen and his students are digging in to better understand what kinds of pathogens might dwell in the burrows. One project includes collecting ticks from the burrows to identify the species and to analyze their blood for infectious diseases that could be transmitted to humans. Another is assessing how the size and layout of a burrow, as well as differences in the vegetation and soil it’s found in, affects which animal visitors stop by.
The paper, Vermeulen says, is a warning from ecologists to epidemiologists: “We’ve shown there is a potential problem — a One Health problem.” To avert a new pandemic, ignoring the interconnection between environment, animals, and people is not an option.
ALSO ON YALE E360
In the Yucatan, the High Cost of a Boom in Factory Hog Farms
