Rabies is generally thought to be universally fatal, but new evidence suggests that is not always the case. A study in Peru suggests that some people -- admittedly a very small percentage of the population -- may have a natural resistance to the rabies virus that protects them from serious illness when they become infected. The results suggest that it may be possible to develop new ways to prevent and treat rabies.
Most Americans associate rabies with dogs, but the virus is most commonly carried by bats. Experts estimate that rabies kills at least 55,000 people each year in Africa and Asia alone, and the disease appears to be on the rise in China, the former Soviet republics, and Central and South America. According to the U.S. Centers for Disease Control and Prevention, U.S. deaths have declined from about 100 per year a century ago to an average of about two per year now, largely due to widespread efforts to vaccinate domestic animals against the disease.
People who have been exposed to the virus are generally advised to seek out post-exposure prophylaxis, a series of injections that activate the immune system to fight off the virus. If initiated quickly, the injections are almost 100% effective. But if the disease gets started, most treatment has proved futile. The exceptions have been two cases, one in Wisconsin and one in California, where intensive therapy pulled the victim through. In Wisconsin, physicians placed the patient in a coma, but that has not worked in subsequent cases.
A team headed by Dr. Amy T. Gilbert of the CDC's National Center for Emerging and Zoonotic Infectious Diseases decided to study residents of an area where rabies is endemic to look for clues about the virus's interactions with humans. In May 2010, they went to the communities of Truenococha and Santa Marta in the Province Datem del Maranon in the Loreto Department of Peru, a region that has suffered several outbreaks of rabies. In South America, rabies is transmitted primarily by the vampire bat, Desmodus rotundus, which lives off of mammalian blood. The bats prefer blood from cows, but if none is available, they will steal it from humans in their sleep, injecting an agent to prevent the blood from clotting. Bats carrying the rabies virus transmit it when they bite cows or humans.
The team reported Wednesday in the American Journal of Tropical Medicine and Hygiene that they detected antibodies against the rabies virus in blood from seven of 63 residents they tested. Only one of those with antibodies reported having been vaccinated, suggesting that the other six had been infected with the virus, but that the symptoms were so mild they did not notice.
"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," Gilbert said. "This means there may be ways to develop effective treatments that can save lives in areas where rabies remains a persistent cause of death."
Such studies, noted Dr. James W. Kazura, president of the American Society of Tropical Medicine and Hygiene, lend "continued support to the belief that even the most dangerous of infectious diseases may be amenable to treatment. Continued investment of resources is essential for us to protect the health and well-being of innocent people whose lives and livelihoods are needlessly threatened by infectious diseases like rabies."
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