Photograph by Joel Sartore, National Geographic
Two thermal pictures show a bat's temperature lowering as a rabies infection takes hold (bright parts are warmer; right image is later). Images courtesy J.A. Ellison et al, CDC/USDA
Published December 19, 2012
A picture is worth a thousand words—or in the case of bats, a rabies diagnosis. A new study reveals that rabid bats have cooler faces compared to uninfected colony-mates. And researchers are hopeful that thermal scans of bat faces could improve rabies surveillance in wild colonies, preventing outbreaks that introduce infections into other animals—including humans.
Bats are a major reservoir for the rabies virus, according to the Centers for Disease Control and Prevention (CDC) in Atlanta. Previous research shows that bats can transmit their strains to other animals, potentially putting people at risk. (Popular Videos: Bats share the screen with creepy co-stars.)
Rabies, typically transmitted in saliva, targets the brain and is almost always fatal in animals and people if left untreated. No current tests detect rabies in live animals—only brain tissue analysis is accurate.
Searching for a way to detect the virus in bats before the animals died, rabies specialist James Ellison and his colleagues at the CDC turned to a captive colony of big brown bats (Eptesicus fuscus). Previous studies had found temperature increases in the noses of rabid raccoons, so the team expected to see similar results with bats.
Researchers established normal temperature ranges for E. fuscus—the bat species most commonly sent for rabies testing—then injected 24 individuals with the virus. The 21-day study monitored facial temperatures with infrared cameras, and 13 of the 21 bats that developed rabies showed temperature drops of more than 4ºC.
"I was surprised to find the bats' faces were cooler because rabies causes inflammation—and that creates heat," said Ellison. "No one has done this before with bats," he added, and so researchers aren't sure what's causing the temperature changes they've discovered in the mammals. (Related: "Bats Have Superfast Muscles—A Mammal First.")
Although thermal scans didn't catch every instance of rabies in the colony, this method may be a way to detect the virus in bats before symptoms appear. The team plans to fine-tune their measurements of facial temperatures, and then Ellison hopes to try surveillance in the field.
This study was published online November 9 in Zoonoses and Public Health.
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