Michaeleen Doucleff

It was a balmy Sunday evening in early 1999, and Dr. Kaw Bing Chua hadn't had lunch or dinner.

There wasn't time to eat. Chua was chasing a killer. And he thought maybe he had finally tracked it down.

He slid the slide under the microscope lens, turned on the scope's light and looked inside. "A chill went down my spine," Chua says. "The slide lit up bright green, like bright green lanterns."

Welcome to the bat cave. No, we're not talking about the secret headquarters of a superhero.

This is Gomantong — an ancient cave carved out of 20 million-year-old limestone in the middle of the Borneo rain forest in Malaysia. It's part of a vast network of tunnels and caverns. And it's the perfect hideout for bats.

Up at the top are millions of bats. Literally millions. They hang upside down all day long from the cave's ceiling, sleeping and pooping.

Pygmy elephants. Monkeys with noses the size of beer cans. And a deer so small you could cradle it like a baby.

And right there, sitting on a leaf, is the strangest bug we've ever seen.

"Check out the size of it," says virus hunter Kevin Olival as he picks up a ginormous roly-poly. "It's the size of a ping-pong ball!"

If you're a germaphobe, make sure you're sitting down.

Back in 1999, a woman in California cleaned up rodent droppings in her home. Two weeks later, her liver started failing. Then she started to bleed internally — a hemorrhagic fever that would kill her. Eventually doctors found a new virus in her body, which very likely came from a rat.

This year we've learned an amazing amount about Zika — how it damages developing brains, how it spreads through sexual contact and where in the world (and the U.S.) it's hiding out.

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