Untreated Rabies May Not Be Lethal for All, Study Says

Some have natural resistance to infection from bat bites, researchers report

August 1, 2012

By Maureen Salamon
HealthDay Reporter

WEDNESDAY, Aug. 1 (HealthDay News) -- Bucking the notion that untreated rabies always proves lethal to humans, scientists studying the virus in isolated pockets of the world have found evidence that either natural resistance or an immune response may stave off certain death for some.

Traveling to the Peruvian Amazon, where outbreaks of rabies infections are spurred by highly common vampire bats, researchers from the U.S. Centers for Disease Control and Prevention learned that 10 percent of natives appeared to have survived exposure to the virus without any medical intervention. Another 11 percent were found to have antibodies in their blood that would neutralize rabies.

"This is a potential game-changer if the study is repeated successfully," said Dr. Rodney Willoughby Jr., a pediatric infectious disease specialist at Children's Hospital of Wisconsin and the author of an editorial accompanying the research. "It suggests either that rabies is not universally severe or fatal [HIV used to be thought of this way] or that there are ways of conferring relative resistance to rabies in humans. If the latter could be identified -- these days, probably through genetic sequencing -- then that might afford insights into prevention or treatment."

The study is published Aug. 1 in the American Journal of Tropical Medicine and Hygiene.

An average of two to four people die in the United States each year of rabies after bites from animals such as bats, dogs or raccoons. Though nearly wiped out in the United States due to domestic animal vaccinations, the infection kills about 55,000 annually in Africa and Asia alone. For those who believe they're infected, a series of shots are 100 percent effective at preventing death.

In Peru, vampire bats regularly seek out meals of mammalian blood from livestock and humans, using extremely sharp teeth and a blood thinner in their saliva aptly known as draculin to feed on sleeping people without awakening them.

CDC researchers interviewed 92 people, 50 of whom reported previous bat bites. Blood samples were taken from 63 participants, with seven found to have rabies virus-neutralizing antibodies. Only one of the seven reported receiving a rabies vaccination, which would generate such antibodies, but no evidence existed that the rest had sought either a vaccination or treatment for a bat bite.

Study author Amy Gilbert, a postdoctoral fellow with the CDC's National Center for Emerging and Zoonotic Infectious Diseases, said the research suggests the rabies virus is not invariably fatal to people.

"Generally, most folks presume we don't develop antibodies to respond to rabies exposures," she said, "but this was a scenario where clearly there were exposures to the virus that did not lead to disease. I think the same recommendations and advice still hold -- that anyone with a bite exposure to a bat or other carnivore needs to seek out post-exposure [injections]."

In his editorial, Willoughby noted two recent cases in the United States (in Texas and California) where children recovered from rabies without intensive treatment after suspected bat bites.

"Knowing that there is a continuum of disease, even for infectious diseases like rabies, should push us harder to try for cures when confronted by so-called untreatable infectious diseases," he wrote. "Modern therapeutics can move us . . . toward greater survival, even when specific cures or antidotes remain undiscovered."