July 16, 2009—Vampire bats in Peru are increasingly biting people, and a National Geographic Society researcher is trying to find ways to stem the resulting spread of deadly rabies. (The National Geographic Society owns National Geographic News.)

Video by Public Television's Wild Chronicles, from National Geographic Mission Programs

Unedited Transcript

MUCH LIKE THEIR MYTHICAL NAMESAKES VAMPIRE BATS MUST FEAST ON FRESH BLOOD EVERY 2-3 DAYS OR DIE OF STARVATION.

THEY SEEK OUT WARM-BLOODED MAMMALS THRIVING OFF DOMESTIC LIVESTOCK LIVING IN THE TROPICAL REGIONS OF SOUTH AND CENTRAL AMERICA.

MOST VICTIMS NEVER FEEL A THING AND THE BITE ITSELF IS SUPERFICIAL.

BUT INCREASINGLY BATS ARE TARGETING HUMANS AND THE ENCOUNTERS ARE TURNING DEADLY.

THE BATS ARE BLAMED FOR RABIES OUTBREAKS IN PERU AND NATIONAL GEOGRAPHIC GRANTEE DANIEL STREICKER IS RESEARCHING THE ENVIRONMENTAL CAUSES AND EXTENT OF THE DISEASE.

"Vampire bats are kind of the perfect storm of different ecological characteristics. On the one hand these bats are feeding on larger mammals which are susceptible to rabies and in order to feed on these animals, to drink their blood, they have to bite and biting is also the main route of transmission of the rabies virus."

STREICKER IS SURVEYING VAMPIRE BATS FROM THE AMAZON RAINFOREST TO THE FARMS ALONG THE VALLEYS OF THE ANDES MOUNTAINS.

VAMPIRE BATS ARE NATIVE TO PERU BUT 500 YEARS AGO SETTLERS IMPORTED AN IDEAL FOOD SOURCE CATTLE.

AND AS THE NUMBER OF LIVESTOCK INCREASES AND SPREADS ACROSS THE COUNTRY SO TOO DOES THE POPULATION OF VAMPIRE BATS.

TODAY LARGE COLONIES THRIVE NEAR AREAS DEVOTED TO RANCHING.

YET DESPITE THE BURGEONING BAT POPULATION ITS RARE FOR PEOPLE LIVING IN THESE AGRICULTURAL AREAS TO BECOME INFECTED WITH RABIES.

RABIES IS A FRIGHTENING AND DEADLY DISEASE.

THE CLASSIC FORM OF THE DISEASE TURNS EVEN DOCILE CREATURES INTO AGGRESSORS THAT FOAM AT THE MOUTH.

BUT THE STRAIN FOUND IN VAMPIRE BATS IS DIFFERENT. ITS KNOWN AS PARALYTIC OR DUMB RABIES CAUSING DISORIENTATION, MUSCLE WEAKNESS AND EVENTUALLY DEATH.

TO LEARN MORE HE MUST TURN THE TABLES. THIS TIME ITS A HUMAN TAKING BLOOD FROM A VAMPIRE.

WORKING AT THE CENTERS FOR DISEASE CONTROL AND PREVENTION OR CDC IN ATLANTA STREICKER ADDS A LAB STRAIN OF THE RABIES VIRUS TO BLOOD SAMPLES HE COLLECTED FROM VAMPIRE BATS IN PERU.

AFTER AN INCUBATION PERIOD THE TEST RESULTS WILL SHOW WHICH BATS HAD BEEN EXPOSED TO THE RABIES.

UNDER THE MICROSCOPE FLUORESCENT GREEN DYE INDICATES NO ANTIBODIES PRESENT MEANING THE BAT WAS FREE OF DISEASE.

BUT IF THE RESULTS COME BACK CLEAR THE BAT HAS ANTIBODIES AND STREICKER KNOWS THE BAT WAS EXPOSED TO RABIES IN THE RECENT PAST.

"This is an important test for us because it allows us to first determine whether the virus is present or absent in a bat population. But finally we can ask some questions at the population level. Specifically asking things like, as you have more livestock in a given area do you see a higher proportion of bats that have been exposed to this virus?"

PRELIMINARY RESULTS INDICATE THAT VAMPIRE BATS FROM AGRICULTURAL AREAS MAY ACTUALLY HAVE A HIGHER RATE OF INFECTION THAN DO BATS FROM OTHER PARTS OF THE COUNTRY.

SO WHY THEN DO SO FEW PEOPLE WHO LIVE NEAR CATTLE RANCHES FALL ILL WITH RABIES IF THERE ARE SO MANY BATS AROUND INFECTED WITH THE DISEASE?

STREICKER BELIEVES THAT THE LIVESTOCK ACT AS A BUFFER BATS PREFER PASSIVE HERDS TO PEOPLE REDUCING THE ATTACKS ON PEOPLE.

BUT AS VAMPIRE BAT POPULATIONS INCREASE AND MORE LIVESTOCK BECOME INFECTED THIS COULD POSE A GREATER RABIES THREAT FOR PEOPLE IN THE FUTURE.

THE SAME THEORY MAY EXPLAIN WHY HUMAN RABIES IS MORE COMMON IN PERUS AMAZON RAINFOREST.

HERE DEVELOPMENT SUCH AS LOGGING, MINING AND ROAD CONSTRUCTION HAS WIPED OUT VAST TRACKS OF HABITAT & REDUCED WILDLIFE POPULATIONS.

AND SINCE THEIRS NOT MUCH LIVESTOCK IN THIS AREA THE BATS TURN TO ANOTHER FOOD SOURCE --- HUMANS.

THERE MAY BE FEWER INFECTED BATS BUT THEY BITE PEOPLE MORE FREQUENTLY.

COULD THIS BE WHY THE DISEASE IS FAR MORE COMMON HERE THAN IN THE ANDES?

THERES MUCH MORE TO LEARN ABOUT HOW WIDESPREAD RABIES IS AMONG THE COUNTRYS BAT POPULATION.

"What we dont know is how this disease is persisting in the vampire bats. And as a correlative to that we dont know where it is in vampire bats. So again much more widespread, potentially it is always present in these bat populations."

STREICKER WILL CONTINUE TO COLLECT DATA HOPING HIS RESEARCH WILL EVENTUALLY HELP PREDICT WHERE PEOPLE WILL NEED TO BE VACCINATED.

THE MORE HE LEARNS ABOUT THIS FRIGHTENING DISEASE THE BETTER THE CHANCE WE MAY SOMEDAY BE ABLE TO CONTROL IT.