Bats are now the primary source of U.S. rabies deaths | Science News for Students

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
Jul 3, 2019 — 6:45 am EST
a bat hanging on a tree

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.

Power Words

(more about Power Words)

anxious     (n. anxiety) A feeling of dread over some potential or upcoming situation, usually one over which someone feels he has little control.

bat     A type of winged mammal comprising more than 1,100 separate species — or one in every four known species of mammal.

Centers for Disease Control and Prevention, or CDC     An agency of the U.S. Department of Health and Human Services, CDC is charged with protecting public health and safety by working to control and prevent disease, injury and disabilities. It does this by investigating disease outbreaks, tracking exposures by Americans to infections and toxic chemicals, and regularly surveying diet and other habits among a representative cross-section of all Americans.

coyote     This relatively long-legged member of the dog family (Canis latrans) is sometimes referred to as the prairie wolf. It is, however, notably smaller and its build more scrawny than a true wolf. Found from Alaska down into Central America, coyotes have lately expanded their range into all 50 U.S. states. Many now hang out in urban areas where they have no predators and can easily dine on rodents and scavenge trashed food.

epidemiologist     Like health detectives, these researchers figure out what causes a particular illness and how to limit its spread.

infect     To spread a disease from one organism to another. This usually involves introducing some sort of disease-causing germ to an individual.

infection     (adj. infectious) A disease that can spread from one organism to another. It’s usually caused by some type of germ.

rabies     (adj. rabid) A virus that is transmitted from mammals such as bats, raccoons, skunks and dogs — sometimes to people. Rabies is found on every continent except Antarctica, and is spread by contact with the saliva of an infected host. A vaccine exists. Without a vaccination, nearly every infected person will die.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

vector     (in medicine) An organism that can spread disease, such as by transmitting a germ from one host to another.

veterinary     Having to do with animal medicine or health care.

virus     Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.

Citation

Report: E. Pieracci et al. Vital Signs: Trends in Human Rabies Deaths and Exposures — United States, 1938 – 2018. Centers for Disease Control and Prevention. Morbidity and Mortality Weekly Report. Vol. 68, June 14, 2019, p. 524. doi: 10.15585/mmwr.mm6823e1.