In 1987, there were about 5 billion people in the world. Now, there are more than 8 billion of us, and we are developing more and more areas for human use. The sometimes porous boundary between wilderness and developed areas; where the suburbs reach into the forest; agricultural areas abut homes; and people are constantly interacting with animals, wildlife, and wild lands is known as the wildland-urban interface (WUI). Although they only compose around 5 percent of Earth's landmass, it's estimated that 3.5 billion people live in these transition zones. And they can be optimal for spreading zoonotic diseases, according to new research reported in Global Change Biology.
In this study, the investigators wanted to know more about how disease spillover is influenced by rapid urbanization in WUIs. As the populations inhabiting these areas grow, it is critical to limit animal and human interaction, to prevent the spread of disease. This is especially important in the Global South, where accelerating development and population growth will be pronounced in the coming years. As people become more connected to each other and to wildlands, there will be serious risks that we are only now beginning to understand, the researchers noted.
“The wildland-urban interface is the perfect place for diseases to emerge because you have people, livestock, and wildlife in these tightly intermixed land use arrangements,” said first study author Rohan Simkin, a graduate student at Yale University. “But there’s plenty of opportunity as cities grow, and this is particularly true in places like Africa and Asia where cities are going to grow rapidly over the next twenty or thirty years, to design cities that avoid a lot of these impacts.”
In this work, the researchers mapped the geographic distribution of around 700 mammals that have been linked to more than 100 diseases that arise in the WUI. This showed that disease-carrying mammals are quite widespread.
There are an estimated 700 million people currently living in areas where about 20 disease-carrying species live. Almost every person living in the global WUI also lives alongside a potential disease host, the study determined.
“Where there is a higher diversity of hosts, you have a diversity of pathogens and more pathways through which people might interact with them,” Simkin said.
Some WUI regions were found to be hotspots, such as large regions in the Northeastern US, or places with huge populations like parts of China. The Global South is also particularly vulnerable, with limitations in healthcare, sanitation, and housing adding to the risk of disease. Unfortunately, data collection is also often limited in this region.
“We have this real lack of knowledge around disease ecology in places where people are actually most vulnerable,” Simkin said. To try understand the threat posed by zoonotic pathogens in WUIs, we need to gather more information from this region.
“The trifecta of urban expansion into wildlands; increased connectivity of people worldwide; and urban growth in places with high pathogens will pose significant disease spillover risks that we are just starting to understand,” added study co-author Karen Seto, a Professor at Yale.
Sources: Yale University, Global Change Biology