Bats are now the primary source of U.S. rabies deaths

Rates of disease are quite low and, unlike elsewhere, seldom due to dog bites

Since the 1950s, bats and other wild animals have replaced dogs as the major U.S. source of human deaths from rabies.

ADAMDV18/Encyclopedia of Life (CC-BY-NC-4.0)

If you have a dog, it will likely have been vaccinated for rabies. But that wasn’t always true. For centuries, dog bites had been a leading source of transmitting the rabies virus. Starting in 1947, though, that began to change as the United States launched a massive campaign to have pet owners vaccinate their dogs. Since then, human rabies deaths due to dog bites and scratches have nosedived. A few Americans still get rabies each year. But these cases are now more likely to come from wild animals, a new study finds — especially bats. 

Emily Pieracci led the new study. She’s a veterinary epidemiologist — a disease detective. She works for the Centers for Disease Control and Prevention, or CDC, in Atlanta, Ga. Since 1960, her team found, bats have caused 62 of the 89 U.S. deaths from rabies. The researchers described their findings June 14 in Morbidity and Mortality Weekly Report.

What makes rabies such a scary disease is its lethality. Without quick treatment after being bit by an infected animal, the virus can move through someone’s body. Eventually it will settle in the brain. An affected person may become confused, delirious, anxious and unable to think clearly. Later, they may become unable to sleep and have hallucinations. It doesn’t matter what animal transmitted the virus, this infection “is fatal in over 99 percent of cases,” the CDC notes. Clearly, it says, this is “one of the world’s most deadly diseases.”

Fortunately, U.S. cases have been falling over the years. In the early 1900s, there were typically about 100 U.S. rabies deaths per year — mostly due to dog bites. Now the U.S. rate is closer to two per year (despite the U.S. population having more than quadrupled over that time). But a lot more people than that fear they could be at risk. The new analysis notes that an average of 55,000 Americans are “treated for potential rabies exposure each year.”

The move to bats

In 2015, CDC noticed that in the United States, bats were surpassing raccoons among animals that tested positive for rabies. The agency also noticed an uptick in the number of mass bat exposures. This is where 10 or more people are exposed to a possibly rabid bat. Such exposures most often occurred where bats had nested in homes, in dorms or around campgrounds. The vast majority of tested bats do not have rabies (usually no more than around 6 in every 100 do). Overall, CDC estimates that fewer than 1 percent of U.S. bats are likely to be infected.

Outside the United States, the risk of rabies can be far higher. Worldwide, CDC notes, some 59,000 people die from rabies each year! Almost all of these cases are due to dog bites. Not surprisingly, the new study notes, dogs are the second most common cause of rabies deaths in Americans who become infected overseas.

People often think infected dogs act aggressively. They worry that these are the dogs who lunge and bark, trying to attack people. In fact, infected animals can be timid and still bite, notes Pieracci. “You can’t tell whether an animal has rabies just by looking at it,” she notes.

In fact, rabid animals may be unusually fearless, she says. “A normal, healthy bat will not allow you to touch it,” she explains. So people should try to stay away from bats, Pieracci says — especially one that doesn’t try to flee from you.

In the wild, rabies also infects coyotes, raccoons, skunks and foxes. To limit these animals as vectors — sources of infection — the U.S. Department of Agriculture has begun a program to vaccinate coyotes, foxes and raccoons.

Carolyn Wilke is a staff writer at Science News for Students. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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