It's the summer months that provide plenty of good reasons for bats to be out and about, experts say.
"The majority of the bats in the U.S. are insect eating," French said. "Their food supply is most abundant in the late spring and early summer."
Pregnant females give birth around that time. By July or August most of the babies finish nursing and begin to leave the roost.
But the young fliers aren't yet skilled at navigating.
"They're much more likely than other bats to end up in the wrong place"like someone's bedroom"this time of year," French said.
Furthermore, people's summertime behavior, such as leaving windows open at night to cool their homes, can invite unintentional encounters.
"An ill bat could find its way into a house that would otherwise be shut," said Charles E. Rupprecht, who heads the rabies program at CDC.
Some kids and other vacationers spend the summer in rustic cabins that have structural holes large enough for bats to squeeze through, he adds.
"Camps are ideal roosts," Rupprecht noted. In effect, "people are inviting themselves into the bats' house. You're invading the bats' domain."
He urges people to exercise common sense and, for instance, not pick up a sick or wounded bat.
"Some people make the mistake of wanting to take care of it," he said.
But simply seeing a bat in one's home isn't usually cause for alarm.
"People sometimes mistakenly believe you couldn't feel a bat bite," French said.
"I've had lots of bat bites, and they hurt. They feel like sharp needle jabs. Any conscious adult is going to know if they're bitten."
Bat bites don't always leave a mark on the skin, so experts worry about possible rabies transmission when a person awakens to find a bat in his or her room.
Unattended children, mentally disabled people, or intoxicated adults might also not notice or properly report a bat bite.
Heat Waves and Hot Zones
Although some people have speculated that intense heat drives more bats indoors, there's probably no link between the recent incident in Virginia and this summer's heat wave, experts say.
But if summers continue to become consistently warmer, it could conceivably increase the frequency of human contact with bats.
That's in part because vampire bats, which now occupy tropical parts of Mexico, might move north under the right conditions, the CDC's Rupprecht says.
"You have to have the right kind of habitatrain forest-type habitat," French, of Bat Conservation International, noted. "[But] there are just too many factors to say if that could happen."
(See a multimedia feature on vampire bats, with photos, video, and more.)
If blood-feeding bats were to spread north, French's hometown of Austin might be among the places they'd end up.
"This is the place, of course, where we have 1.5 million bats right in the heart of the city," she said. "We have the biggest urban bat colony in the world."
And, she added, "we've never had a rabies case here."
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