While enjoying a night boat ride on New Hampshire's Lake Winnipesaukee with friends, Adam Giroux suddenly felt something crawling up his leg. He jumped up, frantically trying to get whatever it was in his pants out of his pants.
"I finally got it out, and we saw that it was a bat," said Giroux, 27. "I wasn't sure if it had bitten me because there weren't really any bite marks. But to play it safe, I went to the emergency room."
Giroux explained his bat debacle to hospital staff. Moments later, doctors began administering rabies post-exposure prophylaxis.
"I got two shots in each arm and four shots directly into my stomach muscles, and then two months later, I was getting follow-up shots every other week," said Giroux. "It was pretty serious, but it was better than the alternative."
While cumbersome and certainly uncomfortable, the shots allowed Giroux to walk away from his bat encounter unscathed.
While most people think of dogs, raccoons or skunks as potential rabies carriers, bats are a major source of the disease in the United States, experts say. And on Thursday, the Centers for Disease Control and Prevention announced that a Mexican teenager had become the first person on U.S. soil to die from rabies after getting bit by a vampire bat.
According to the CDC's Morbidity and Mortality Weekly Report, the 19-year-old man arrived to work on a Louisiana sugar cane plantation in July 2010. After one of day working in the field, he began to experience fatigue, pain in his left shoulder and numbness in his left hand. His condition gradually worsened, and on Aug. 21, he died of rabies. After public health officials interviewed friends and family, they figured out that he had been bitten by a vampire bat in Mexico, 10 days before arriving in the U.S.
"This ... highlights the importance of a global perspective for human rabies prevention and the changing epizootiology of rabies," the Centers for Disease Control and Prevention wrote in the report. "Since 2000, eight of the 32 human rabies cases reported in the United States (including the case described in this report) were acquired from exposures abroad."
The rabies virus has an average incubation period of 85 days. In this case, symptoms showed within 15 days.
Once exposed, the rabies virus makes its way to broken nerve endings, then works its way back from the bite site toward the spinal cord.
"Once it's in the central nervous system, it attaches to the brain," said Dr. William Schaffner, chairman of preventive medicine at Vanderbilt University Medical Center. "Then there is inflammation of the central nervous system, and a person will get interference in the way they think and eventually lapse into a coma."
Experts say that as soon as exposure to a rabid animal is suspected, it's important to consult a doctor and receive a post-exposure prophylaxis vaccine. The vaccine will prevent them from getting rabies, which is almost always fatal.
"Because the rabies virus takes weeks to incubate, there is time for the vaccine to prevent disease even when given after exposure to the virus," said David Topham, associate professor of microbiology and immunology at University of Rochester Medical Center. "The man's death could have been easily prevented if he'd sought treatment in time."
But as this vampire bat continues to make headlines, it's important to understand that there are bats already carrying the deadly rabies virus in the United States.
In 2009, U.S. health officials tested 30,000 bats from several dozen different species for rabies. Dr. John Williams of the department of pediatric infectious disease medicine at Vanderbilt said that 6 percent, or about one out of 15 bats, tested positive for rabies.
"A lot of times, people don't even recall being bit by a bat," said Williams. "The bites are small and not particularly painful. But even if someone handles a wild bat, they should receive the prophylactic vaccine because bats shed a lot of the virus through urine and other secretions. They don't even have to bite to infect."
In the report, the CDC concluded that vampire bats may expand and migrate because of climate changes.
"Expansion of vampire bats into the United States likely would lead to increased bat exposures to both humans and animals (including domestic livestock and wildlife species) and substantially alter rabies virus dynamics and ecology in the southern United States," the CDC wrote.
But experts said those changes are complex and difficult to predict.
"My concern about invoking climate change as the basis for predicting future increases in human illness is that it's a lot like the medieval clerics' claim that plague would come as a result of human sin: It's apocalyptic, it's irrefutable and it's easily turned into admonitions about individual behavior," said Philip Alcabes, a professor of public health at Hunter College.
"So let me say that expansion of the vampire bats' range might have to do with climate, but if so, it's complex," said Alcabes. "It is not going to depend on whether you recycle newspapers or not."
But he did note that scientists must understand a complex ecosystem when trying to understand an infectious organism.
"What's needed is more environmental monitoring, including information about prevalence of different viruses in various animal species as well as data on land use, weather and so forth," said Alcabes. "This would allow for a richer understanding of how transmission of viruses to humans, as in this unfortunate case, arises from changes in ecosystems."