Are all emerging viral diseases of the past 100 years zoonoses?

Most new viruses that have appeared in the last 100 years came from animals, like your pet dog or cat.

Think of it this way: when a virus moves from an animal to humans, it's kind of like sharing a toy. If a virus lives inside a bat, and then jumps into a human, that’s how some diseases start. This is called a zoonosis, which means the disease came from animals.

Sometimes, viruses hang out in one animal for years, like a bat living in a cave. If humans get close to those animals, maybe by cutting into their meat or getting bit, the virus can move into people.

Other times, the virus might even use another animal as a "middle man." For example, a bird could carry the virus from one place to another, and then give it to humans when they come near.

But not all new viruses are zoonoses. Some can start in people, like when a virus changes inside someone’s body or jumps between humans through coughs or sneezes.

So, most, but not all, of the new diseases we’ve seen in the past century started with animals sharing their germs with us.