The big bats have been common in that part of Australia for twenty million years. But as the rain forests that were their natural habitat were fragmented by roads, logging, and farms, and their food sources became more and more difficult to locate due to a changing climate, they moved into civilization. They roosted in the trees in the pasture, contaminating the grass with their urine, which was laced with a virus that nobody had ever seen before—it would become known as Hendra virus. It leapt to the horses, which had grazed on the grass, and then to the humans who cared for them.
