City-dwelling mammals no likelier than wild mammals to harbor human diseases

Monkey on stupa at Swayambhunath temple iconic landmark Kathmandu Nepal
Rhesus Macaques monkeys on the ancient stupas of Swayambhunath temple high above Kathmandu, Nepal. (iStock)

As our world becomes über urbanized, researchers have suggested there may be an increasing risk of urban-adapted mammals passing their viral pathogens to people.

This assumes that mammals adapted to living in urban environments carry more viral pathogens capable of infecting people than their wild counterparts, and that they have more opportunity to pass these zoonotic pathogens to their human neighbors.

But what does the evidence say?

A group of researchers with VERENA—the Viral Emergence Research Initiative, a global virtual consortium focused on predicting the next disease outbreak from animals to people—decided to take a closer look. Members of VERENA span disease, community, viral, and evolutionary ecology; computational and veterinary biology, immunology, and arbovirology. University of Florida College of Liberal Arts and Sciences professor Sadie Ryan contributes her expertise as a medical geographer. Ryan is a faculty member in the UF Emerging Pathogens Institute.

The group set out to test the idea that urban-adapted mammals carry more pathogens capable of being transmitted to people than wild animals. They scoured major open-access databases for information about 3,000 mammal species, including their phylogenies and geographic data.

In new works published in Nature Ecology and Evolution, the team found that urban mammals had more pathogens than wild mammals, and that they were better studied than their wild counterparts—especially in Europe and North America. 

“We found that urban areas are worse for pathogens, but many of these pathogens are not necessarily zoonotic ones that can harm people,” Ryan said.

Because urban mammals were over-represented in the data compared to wild mammals, the team used statistical methods to correct for sampling bias. When this adjustment was made, urban and wild mammals carried roughly the same amount of viruses. But one difference that remained had to do with the variety of pathogen species present, what ecologists term species richness.  

Urban mammals were found to have more pathogen species richness than wild mammals, but – and this is key – they did not have comparatively more zoonotic richness. In other words, urban mammals were not found to pose any greater risk than wild mammals when it came to transmitting viruses capable of infecting people.

“We thought urban mammals would have more pathogens and more zoonotic ones,” Ryan said. “But it turns out the data does not support that. It’s not the results we thought we would find!”

And maybe that’s a good thing for global public health.

By: DeLene Beeland