How to Stop a Virus That Goes From Bats to Horses to Humans

It's a deadly chain: Bats in Australia harbor a virus called Hendra, which doesn't hurt them but can be passed to horses via urine or feces—and those animals fare far worse. There's a 75% fatality rate, though cases are fairly rare. Even more rare is the transmission to humans, which can happen to those who treat the sick horses. NPR reports there have only been seven documented cases of humans contracting Hendra virus, but four of those people died (monoclonal antibodies have turned out to be effective in preventing infection after exposure). Still, "the possibility of an outbreak could be devastating," says Raina Plowright, a disease ecologist at Cornell who is the subject of NPR's fascinating article and the author of a new study published in Nature.

She headed to Australia with a question: Under what conditions was spillover—in which a virus moves from one species to another—more likely? As a starting point, she needed to catch bats called red flying foxes, take blood samples, and get a sense of how many harbored the Hendra virus. To her surprise, she found the bats had almost none of it. The a-ha moment came in 2006, when she struggled to find bats for testing. A cyclone had destroyed much of their nectar sources, and the lack of food decimated populations. She managed to capture and test a few dozen and found sky-high levels of Hendra virus. Further research confirmed her theory that emaciated bats "don't have enough energy to maintain an immune response to keep these viruses in check."

Deforestation and climate-related food shortages don't just lead to elevated virus levels; the lack of food also drives the bats toward places like farms in search of food—putting them in close proximity with horses. Plowright has since determined that an effort to plant a few plant species that flower in winter can make all the difference—as the Verge puts it, "Giving a bat flowers might preempt a pandemic." The New York Times' take: "The idea that deforestation can increase the risk of disease spillover is not a new one ... but the new research is an extraordinarily detailed case study ... unpacking precisely how environmental changes can drive disease risk—and how and where experts might be able to intervene." (More discoveries stories.)