Common belief says that a bite from a rabies-infested animal can lead to death unless immediate treatment is given. A new study has challenged this idea by finding cases where people did not receive medical treatment and have survived after being infected with rabies.

The study was conducted in a region in the Amazon, where vampire bats are known to attack humans and pass on the virus.

"The overwhelming majority of rabies exposures that proceed to infections are fatal. However, our results open the door to the idea that there may be some type of natural resistance or enhanced immune response in certain communities regularly exposed to the disease. This means there may be ways to develop effective treatments that can save lives in areas where rabies remains a persistent cause of death," said Amy Gilbert with the CDC's National Center for Emerging and Zoonotic Infectious Diseases, and the paper's lead author.

Rabies is a zoonotic disease (a disease that can be transmitted from animals to human) caused by viruses of the Lyssavirus genus. Rabies has the highest case of fatality ratio of any infectious disease if prompt PEP is not initiated.

Post-exposure prophylaxis (PEP) is the washing of the wound followed by passive immunization with rabies immune globulin, and a series of four doses of rabies vaccine.

"We all still agree that nearly everyone who is found to be experiencing clinical symptoms of rabies dies. But we may be missing cases from isolated high-risk areas where people are exposed to rabies virus and, for whatever reason, they don't develop disease," Gilbert said.

Researchers found that 11 percent of the people in a study group in this region were naturally resistant to the infections.

An estimated 55,000 people are killed by rabies each year. In the U.S., cases of rabies have been brought down from 100 annually to an average of 2 cases per year.

They say that analyzing the genetic factors that have made these people fight the disease could help find new ways to treat the disease in the general population.

The study was published in the American Journal of Tropical Medicine and Hygiene.