By Lena Sun

The Washington Post

BAT CAVE, QUEEN ELIZABETH NATIONAL PARK, UGANDA — By day, some of the most dangerous animals in the world lurk deep inside this cave. Come night, the tiny fruit bats whoosh out, tens of thousands of them at a time, filling the air with their high-pitched chirping before disappearing into the black sky.

The bats carry the deadly Marburg virus, as fearsome and mysterious as its cousin Ebola. Scientists know that the virus starts in these animals, and they know that when it spreads to humans it is lethal — Marburg kills up to 9 in 10 of its victims, sometimes within a week. But they don’t know much about what happens in between.

That’s where the bats come in. No one is sure where they go each night. So a team of scientists from the U.S. Centers for Disease Control and Prevention traveled here to track their movements in the hopes that spying on their nightly escapades could help prevent the spread of one of the world’s most dreaded diseases. Because there is a close relationship between Marburg and Ebola, the scientists are also hopeful that progress on one virus could help solve the puzzle of the other.

“We want to know where they’re going on a nightly basis,” said Jonathan Towner, 52, who heads a CDC team that specializes in how these deadly viruses are spread. If the animals are feeding on particular fruit trees, that information could identify communities most at risk and help prevent future outbreaks. “It’s much easier to put together a picture and say to local authorities, ‘Look, this could be potentially how the virus is spread, this is what the bats are doing.’”

U.S. officials are so concerned about Marburg becoming a global threat that the CDC is asking the Pentagon’s Defense Threat Reduction Agency to pay for the bat trackers, which each cost about $1,000. The CDC is hoping to track more of these Rousettus aegyptiacus bats in several other caves in Uganda.

Marburg’s potential to spread was made clear a decade ago when a pair of tourists on separate trips walked into the cave looking for adventure and walked out with the virus. A Dutch woman died 13 days after her visit. The other visitor, an American woman named Michelle Barnes, survived after a long, painful illness. The cave was closed to tourists in 2008.

Marburg was identified in 1967 when a shipment of infected African green monkeys from Uganda was sent to laboratories in Marburg and Frankfurt, Germany, and Belgrade, in then-Yugoslavia. Seven lab workers died within about a week. Since then, a dozen outbreaks have been reported, killing hundreds of people. Most took place near bat-infested caves or mines, including one last fall along Uganda’s eastern border with Kenya. Of four family members sickened, only one survived.

For the CDC scientists, success hinges on getting the tracking units, which are half the size of a pen cap, to stay on a bat body that is only about six inches long. A practice run in Atlanta with the same device on the same kind of bat in a special CDC laboratory failed. Trackers slipped off or were chewed by the bats.

“I have no idea how well this is going to go because it’s the first time we’ve tried it,” Towner said. “It could end up in total flames.”

Before you see the bats — about 50,000 live in the cave — you hear their squeaks and chatter and smell the ammonia from their guano, which covers the cave’s rocky floor. One false step can lead to a fall into a stream underneath.

Towner and CDC colleague Brian Amman, 54, discovered a decade ago that this Egyptian fruit bat is a natural reservoir for Marburg. That means the virus can live and grow inside the bats without harming the animal, and be excreted in its urine, feces or saliva.

The bat team includes CDC scientist Jennifer McQuiston and Luke Nyakarahuka, an epidemiologist at the Uganda Virus Research Institute, a longtime CDC partner. The CDC allowed a Washington Post reporter and photographer to accompany the team.

In a clearing of the Maramagambo Forest, the scientists’ workstation is a table under a tent. Curious baboons perch on nearby tree stumps. Black-and-white colobus monkeys peer from overhead branches. On a drive through the park in search of other bat roosts, the scientists’ Toyota Land Cruiser yields the right of way to a majestic waterbuck, its long, curved horns glinting in the sun.

Their task is to catch and glue trackers on 10 bats the first day, repeat the next day.

The tracking software has prompted a stream of curses from Amman. To test it again, McQuiston and Nyakarahuka each cup a tiny unit in their palms and jog around the clearing to simulate bats on the move.

“If it comes back and says zero, I don’t know what we’re going to do,” Amman mutters. Several minutes pass in silence. Then, ever so slowly, data points start to show up.

Towner and Amman suit up in special helmets and face shields connected to battery-powered respirators that muffle their voices. Underneath protective gowns they wear Kevlar-lined waist-high pants to guard against snake bites. On their hands are cut-resistant leather gloves, like those worn by law enforcement, over two pairs of medical gloves to protect against bat bites.

Amman, holding a net, heads to where Towner is pointing, veering far away from an enormous python. He returns with two bats, which go into a pillowcase Towner is holding. Each pillowcase will hold about five bats since bats don’t like to be alone.

Towner lifts the first bat out of a pillowcase, cradling it in his gloved hands. The bat is calm. Its big brown eyes blink, unaccustomed to the light. Towner squeezes a thin line of glue on its back, another line of glue on the tracker and presses down gently but firmly.

For several long seconds, no one utters a word.

Towner breaks the silence. “That’s on pretty good,” he says softly, flicking at the device.

“WOO-HOO!” Amman shouts, relief washing over his face. Up go his arms, signaling a touchdown.

“I’m so happy, Jon,” he gushes. “This is just better than Christmas.”

Now the scientists wait, unsure whether the batteries will last, whether the signal will be able to break through cloud cover to reach the satellite, whether technology will be able to capture this crucial flight of nature.

Amman calls after the bat: “Bring us back some data!”