As climate change contributes to a surge in disease outbreaks across the world, scientists warn that current rates of environmental degradation and biodiversity loss will lead to more deadly pandemics like the coronavirus.
The total number of disease outbreaks has more than tripled each decade since the 1980s. More than two thirds of the diseases originated in animals and most of those were directly transmitted from wildlife to people.
Habitat destruction like deforestation and agricultural development on wildland are increasingly forcing disease-carrying wild animals closer to humans, allowing new strains of infectious diseases to thrive.
"When you cut down trees and remove the forest, you eliminate the natural environment of some species. But those species don't just disappear," said Roger Frutos, an infectious diseases researcher at the University of Montpellier in France.
"We instead create a patchwork, a mosaic of their environment that's closer to ours, with houses that attract insects or sheds where bats can rest and find shelter," he said.
Scientists say the coronavirus pandemic is the most recent instance of how human degradation of wildlife habitats is linked to the spread of infectious diseases. Research has found that Covid-19 likely originated in a horseshoe bat and was then transmitted through another animal.
Bats are less likely to transmit viruses to humans when they are in wild habitats, but land conversion has increased their exposure to humans and upped the chances of virus transmission. There's now a higher density of bat-borne viruses and pathogens near human dwellings worldwide, according to Frutos.
Some researchers estimate that more than 3,000 strains of coronavirus could already exist in bats and could be transmitted to humans.
"When you're building human homes right up on forest edges, you're destroying wildlife habitats and squeezing animal habitats into smaller areas," leading to a more likely transmission of disease to humans, according to Tierra Smiley Evans, an epidemiologist at the One Health Institute at the University of California.
Only about 15% of the world's forests, which are key to maintaining biodiversity, remain intact after degradation from logging, fires and agricultural expansion, according to the World Resources Institute. Millions of animal and plant species currently face extinction because of habitat destruction.
South America is a prime area of concern over infectious disease spread due to rapid deforestation of the Amazon rainforest from logging and mining, which researchers say will aggravate wildfires and Covid-19 spread in the region.
"Preserving habitats for wildlife and preserving our world is a human health issue, not just a wildlife or environmental issue," said Smiley, who studies deforestation and virus spread in Myanmar.
Scott Weaver, director of the Institute for Human Infections and Immunity at the University of Texas Medical Branch in Galveston, said deforestation will increase the risk of many mosquito-borne viruses in areas like the tropics, Latin America and Southeast Asia.
Poorer countries will suffer the most from diseases made worse by climate change, since warmer temperatures will increase the spread of viruses like dengue fever in places where people can't afford air conditioning and general protections against disease exposure, Weaver said.
For instance, the West Nile virus, a mosquito-borne disease, replicates a lot faster in hotter climates. Researchers believe that global warming is allowing the virus to spread more efficiently in wild birds, who then infect people.
"We're in this predicament with the coronavirus because we've under invested in public health across the world and we haven't taken scientific information into account in political decisions," Weaver said.
There are more than 3.8 million confirmed Covid-19 cases across the world and at least 269,881 people have died from the disease, according to data by Johns Hopkins University.
"Hopefully the awakening from this Covid-19 pandemic will get people paying more attention to scientists telling us about these risks that could spill over into vector-borne diseases," Weaver added.