An infection untreated rabies is generally considered a death sentence. But a new study by scientists at the Centers for Disease Control and Prevention (CDC) in Atlanta suggests that may be wrong. In two villages in the Amazon, researchers found that 10% of those tested seems to have survived an infection.
The results are "surprising but convincing," said Hildegund Ertl, a vaccine expert at the Wistar Institute in Philadelphia. The study could be a "game changer," said Rodney Willoughby, a pediatrician at the Medical College of Wisconsin in Milwaukee. "If these results are confirmed and extended, it would show that rabies can vary in severity, rather than 100% fatal."
Rabies is supposed to kill more than 55,000 people each year in Africa and Asia alone, each after a bite of a rabid dog. In Latin America, most human cases are caused by vampire bats. Although these animals usually feed on cattle, they are known to bite sleeping humans.
A vaccine against rabies is available, but it is very expensive and usually given only to people who are at high risk, such as veterinarians in countries affected rabies. The only way to survive an infection or scientists believed-is treatment with antibodies and vaccination immediately after a bite from an infected animal.
However, there have been sporadic reports of people who survive an infection even without these measures. For example, previous studies have provided weak evidence of rabies infections in the last Inuit hunters or fox trappers, said Ertl. Some of these people seemed to have antibodies against the rabies virus in the blood, but the amount was too small to be confident about the results, she said. And in May 2011, an 8-year-old girl in California diagnosed with rabies may be contracted from a cat loose in his school survived without treatment. But Willoughby, who saved a girl infected with rabies in 04 with an experimental treatment, said he has not convinced the California girl really had rabies. "We have other laboratory tests in patients in California, which campaigns against rabies, but the methodology is being validated," he wrote in an email.
The new study suggests that survivors of rabies can be quite common. In May 2010, CDC scientists visited two villages in the Amazon region of Peru, in the west, where infections with rabies have been reported several times in recent years. They interviewed 92 people in 51 households and collected blood samples from 63 of them. The samples were frozen, shipped back to Atlanta, and then screened for antibodies that could bind and neutralize the rabies virus.
Seven of the 63 blood samples tested positive. One of these subjects had told the team he had been vaccinated, but the other six said they were not, suggesting their immune system had learned to deal with the deadly virus on its own, the reports of the team today the American Journal of Tropical Medicine and Hygiene .
Willoughby suspect that the relative strength may be unique to the remote Peruvian population. It may be genetic, nutritional, or on the basis of unknown coinfection. But although the study sampled a very isolated population, there is no evidence that the Peruvians were genetically special, Amy Gilbert said the CDC National Center for Emerging and Zoonotic Infectious Diseases and lead author of the paper. People who had protective antibodies in their blood tend to be older, however. "We believe that [likely] more explanation is that these people were exposed to low doses several times virus" by contact with bats, she said. Unlike some survivors reported cases of infection patients, Peruvians seem to have no ill at all. asymptomatic people generally go to a clinic after a bat bite only because the nearest hospital is a long distance by water so their infections can often go unnoticed, Gilbert said.
Ertl said the study results are "much stronger" than those of the Inuit people, leaving little doubt that some people can indeed survive rabies. But different animal species carry different strains of the virus. "I do not think this could happen in a person of dog rabies," warns Ertl. "To me, it looks like the bat is a little wimp."
And in all cases, Ertl warns, one should think of rabies as less dangerous after this document and any the world bitten or scratched by a bat should receive the vaccine as soon as possible.
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