Hendra virus rarely spills from animals to us. Climate change makes it a bigger threat

PO1 William "Chip" Nagel
..."Not quite 20 years ago, Raina Plowright stood in a forest in Australia's Northern Territory at dusk. She watched as hundreds of thousands of bats called little red flying foxes launched themselves into the air.

"The sky was [dark] with these huge bats taking off in this stream of animals across the landscape looking for nectar," Plowright says. "So just a deafening roar of bat sound, talking to each other, screeching at each other."

Plowright, a disease ecologist at Cornell University who studies pandemic prevention, was interested in bats because they carry a virus called Hendra. And while it's harmless to bats, they can pass it to horses through their feces and urine.

For equines it manifests as a nasty respiratory and neurological disease. They can develop a frothy nasal discharge, trouble breathing and odd behaviors, like drinking water constantly or throwing themselves against the wall of a stable. The virus kills three out of every four horses it infects. Over 100 horses have died from Hendra, though there are no known cases at the moment.

And it's not just a problem for horses. "When people treat sick horses," says Plowright, "that's when people get sick. That's when people get Hendra virus."

Fortunately, Hendra doesn't spread easily among humans. There have only been seven documented cases, but four of them were lethal. And each time a virus jumps from animals to humans — in this case, from bat to horse to person — it gets another chance at evolving and becoming more infectious.

With such a severe human fatality rate, the possibility of an outbreak could be devastating. "I mean, we're talking about a catastrophic, civilization-changing event," Plowright says.

But there are signs that Hendra can be tamed. "More recently, anyone with significant exposure to Hendra virus has been treated with monoclonal antibodies and so they have not become infected," she says."...