Amazon Study Reveals that Untreated Rabies May Not be Lethal

In an apparent reversal of a commonly held belief, people in two communities in a remote part of Peru’s Amazonian region have survived after being exposed to rabies even without being vaccinated, according to a study by the Center for Disease Control and Prevention.

The study, “Evidence of Rabies Virus Exposure among Humans in the Peruvian Amazon,” speculates that while avoiding rabid animals and receiving injections administered after a person is exposed to rabies virus are the best way to protect oneself against the fatal disease, people living in certain communities where they are regularly exposed to the virus may develop an immune response to rabies.

“Nearly all rabies virus exposures that proceed to clinical infections are fatal,” said Amy Gilbert, PhD, of CDC’s National Center for Emerging and Zoonotic Infectious Diseases. “Our results support the idea that under very unique circumstances there may be some type of enhanced immune response in certain populations regularly exposed to the virus, which could prevent onset of clinical illness.”

The CDC study, which was conducted in collaboration with the Peruvian Ministry of Health, surveyed 92 people, 50 of whom reported previous bat bites. Of the 63 people whose blood was sampled, 11 percent had “rabies virus neutralizing antibodies.”

Despite what seems like a low percentage in general, only between three and 20 percent of bats contain the rabies antibody and humans are not reconsidered "reservoirs" of rabies.

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"You wouldn't expect humans with the antibody to fall into even three percent of population," Gilbert said.

While researchers were unable to tell when people were exposed to the virus or what animals were responsible, the area is flush with vampire bats and many residents reported being exposed to multiple bat bites.

"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, according to U.S. News and World Report. "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.

Earlier this year, seven indigenous children in Peru died from rabies contracted through bat bites. In 2010, a rabies outbreak saw 20 Peruvian children succumb to the virus, while several children died last year.

The outbreak’s caused the Peru’s Health Ministry to issue a mass vaccination program, with authorities purchasing over 180,000 does of the vaccine.

In the CDC study the majority of people who had the rabies antibody were of an older age.

"Most likely its related to the exposure and the frequency of the exposure," said Dr. Brett Petersen of the CDC. "My suspicion is this would happen to anybody put into this environment."

Rabies has been recorded throughout history for over 4,000 years. The virus is most prevalent in rural areas and while dogs remain the main culprits in the spread of rabies, bats, raccoons, skunks and foxes are also known to transmit the disease.

At its onset rabies causes flu-like symptoms such as fever, headache, and general weakness before progressing to more specific symptoms such as insomnia, anxiety, confusion, slight or partial paralysis, excitation, hallucinations, agitation, hypersalivation (increase in saliva), difficulty swallowing, and hydrophobia (fear of water).

Death occurs within a few days of the onset of the more severe symptoms. Over 55,000 people a year die due to rabies, the CDC reports.

“In the United States, human deaths from rabies have declined over the past century from more than 100 annually to an average of two per year because of aggressive campaigns to vaccinate domestic animals against the disease,” according to the CDC.