That was the title of a column published under the rubric of "killer viruses" by the US National Public Radio. It focused on the Gomantong Cave in Borneo, and presumably other large caves in the world, where great numbers of bats congregate. Bats are vital for keeping the rain forest alive — they are key pollinators for more than 500 kinds of plants. But as people spread out around the globe to visit these caves, they are increasingly coming into contact with bats and the viruses they carry in their excrement — called guano. The article focuses on the potential for the appearance of unknown viruses that might cause a pandemic that could kill millions.
This is the link to the complete NPR article: The Next Pandemic Could Be Dripping On Your Head
The accompanying photo is from the NPR article.