Bats Incredible: The Mystery of Rabies Survivorship Deepens

Until recently, a human rabies infection was considered inescapably fatal. But a teenage girl who defied this death sentence eight years ago has had doctors and scientists debating how she survived ever since. And now a surprising report from remote Amazonia is adding to the mystery.

In our feature for Wired this month, we explore the controversy over the Milwaukee Protocol: an experimental treatment regimen for rabies that may have saved the teenage girl in 2004 and five more patients since then. But many top rabies scientists still doubt whether the treatment method, which involves inducing a medical coma, is the best way to treat rabies patients.

Central to their doubts is the question of whether some humans might well have been surviving rabies without treatment all along. No other disease kills every single human it afflicts, after all. And studies in dogs and bats have shown that those rabies carriers, who almost always die from the infection, nevertheless will occasionally survive.

Now a new study provides more ammunition for the idea that humans might survive rabies on their own.

A research team led by Amy Gilbert of the U.S. Centers for Disease Control and Prevention studied two communities in Peru where vampire bat attacks on cattle are common. Of 63 people tested, seven of them came back positive for virus-neutralizing antibodies against rabies — and only one of them had ever received rabies vaccination, which would induce the immune system to create the antibodies. That fact strongly suggests that the other six produced the antibodies after being exposed to rabies but failed to die from the illness. And indeed, most of the seropositive Peruvians reported that they had been bitten by a vampiro at least once.

As the authors note, this is one of the first (and definitely the strongest) study to show that humans can naturally develop rabies antibodies without dying from the disease. But does this settle the debate over rabies survival? Probably not.

Since the 19th century, it’s been known that not everyone who gets bit by a rabid animal will come down with the deadly brain infection. In many cases — probably in most cases — of a rabid bite, the virus never actually gets to the brain. It might be that virus replication occurs at the site of the bite but the immune system clears the infection. Or it might be that the immune system is exposed to defective or incomplete virus particles that are able to provoke antibodies against rabies but unable to replicate.

Almost certainly those seven Peruvians were bit by rabid vampire bats, and developed an immune response against rabies as a result. But the study doesn’t investigate whether they experienced any of the neurologic symptoms of the disease, which progress from fevers and malaise to hallucinations, difficulty in swallowing, and worse. And absent a report of those symptoms, it’s impossible to say whether they ever developed the brain infection that doctors generally mean when they say a patient “has” rabies.

Read more at Wired Science