Last year a team of researchers from Peru and the U.S. made a discovery that challenged one of the most widely held assumptions about rabies—that the virus is nearly always fatal unless doctors administer a vaccine before it reaches the brain. Based on the results of blood tests, the scientists learned that half a dozen villagers in a remote part of the Peruvian Amazon had previously been infected—probably through bites from vampire bats, which are common in the area. But instead of suffering the agonizing deaths for which rabies is infamous, the villagers had recovered and apparently developed immunity to further infection.
The discovery put the Peruvians on a short list of people who have survived rabies without a vaccine. The best-known member of that select group is Jeanna Giese, a Wisconsin teenager who lived through the disease in 2004, also after contact with a bat. Out of desperation, Giese's physician improvised a risky treatment that included putting the girl into a controlled coma, which apparently allowed her body enough time to destroy the microscopic intruder. Doctors have since refined the treatment, now known as the Milwaukee protocol, and tried it on at least 39 other never vaccinated patients. Five more people have survived.
The mixed success rates, and the 2012 Peruvian study, underscore how little scientists know about rabies, despite its long history as a menace to humanity. Based on accumulating evidence, though, researchers now recognize that not all rabies infections are equal or universally fatal. Many different animals, including dogs, bats, foxes and raccoons, carry various strains of the rabies virus. The varieties hosted by bats and foxes appear to be weaker, and some people's immune systems may be able to defeat them without a vaccine. Dogs, however, carry a more virulent strain that has rarely been vanquished without medical intervention. To this day, canines remain the largest and most dangerous group of rabies carriers worldwide.
Even if doctors one day perfect a treatment for the later stages of rabies, the procedure would likely be complicated and expensive. Most public health experts think that the best way to control rabies is to vaccinate the most dangerous hosts: all domestic and stray dogs, particularly in the developing world. One such veterinary program in the Philippines has dramatically reduced deaths among humans, and others are under way in India and Tanzania.
Rabies kills about 55,000 people every year worldwide—an admittedly smaller toll than, say, AIDS or influenza. The virus's horrific reputation is nonetheless richly deserved. Symptoms emerge slowly in anywhere from a few weeks to—in rare cases—more than a year after contact with a rabid animal. The rabies virus crawls from nerve cell to nerve cell, eventually making its way from the site of the bite or wound to the brain. Fatigue, fever and chills gradually give way to hallucinations, anxiety, violent convulsions and the telltale foaming at the mouth once the virus reaches the salivary glands. Death is painful and terrifying, which is why standard medical practice calls for keeping patients sedated in the last phases of the disease.
Louis Pasteur's development of a rabies vaccine in 1885 prevented such gruesome outcomes if doctors acted quickly. (More than a century later most rabies deaths in the industrial world—including one or two each year in the U.S.—occur because a bite was not recognized or not taken seriously.) But his success had an unintended consequence: as explained in the 2012 book Rabid: A Cultural History of the World's Most Diabolical Virus (Viking Adult), rabies became a low priority for the budding field of biomedical research.
So when 15-year-old Giese entered Children's Hospital of Wisconsin in Milwaukee in 2004 with full-blown rabies, one month after a bite from a bat flitting around her church, there was still no successful treatment. She was feverish, semiconscious and jerking involuntarily.