While the exact source of COVID-19 remains unclear, zoonotic diseases like COVID-19 — diseases that originated in animals — are a stark reminder of how people and nature are interconnected. Other serious outbreaks, such as SARS, avian flu, and MERS, were all zoonotic in origin. Animals aren’t to blame for these outbreaks. It’s human activities that encroach unsustainably into wild places and risky interactions with wildlife that create increased risk.

Zoonotic disease spillovers like this occur when a disease jumps from animals—wild or domestic—to humans. Any number of interactions can lead to spillover events: a hunter transporting the meat of a wild animal shot in a forest near home, a farmer tending to the family's livestock at forest’s edge, or a vendor selling goods in an urban market.

The “spillover” of a zoonotic disease to a person can occur when a person is bitten by a wild animal; when someone is exposed to feces, blood, or saliva of a wild animal or of a domesticated animal that has been exposed to a wild animal; or simply from breathing aerosolized virus coming from sick animals in a wildlife market or elsewhere.

Most pathogens that inhabit animals pose a minor threat to people. However, novel zoonoses—meaning those which have not been previously identified—are emerging with increasing frequency.

Experts define pandemic hotspots as places where higher concentration of conditions come together to create greater risk for spillover events. [2] This field of scientific research is still evolving, but research suggests greater risk for zoonotic spillover happens in:

Places with high levels of biodiversity, like the tropics, where large scale deforestation is happening. [3] [4]

Places where the trade and farming of wild animals is common, putting people and domestic animals in sustained, close contact with wildlife.

Places where the trade and farming of wild animals is common, putting people and domestic animals in sustained, close contact with wildlife. [5]

Why does there seem to be an occurence of almost 3x more of such spillover events happening in the last 20 to 30 years? What is different now?

The answer to this question may be found by better understanding our changing relationship with nature. As humans push into the last blocks of natural habitats, especially tropical forests, we encounter more and more novel viruses and pathogens that may be a risk to people. People settling and working in newly opened forests interact with these new diseases.

Expanding agriculture, expanding human settlements, and global market pressures are leading to increasing deforestation and conversion of habitats. And, deforestation and conversion are more likely to occur in places where there is a growing expansion of road networks. [10]