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Workers dressed in protective clothing outside a hospital in Uganda.

World Health Organization officials prepare to enter Kagadi Hospital in Uganda on July 28.

Photograph by Isaac Kasamani, AFP/Getty Images

Ker Than

for National Geographic News

Published July 31, 2012

A recent outbreak of the deadly Ebola virus in Uganda highlights the many unknowns of the highly contagious fever, experts say.

(See more health news.)

The latest Ebola occurrence is thought to have started in Uganda's western Kibaale District about three weeks ago, but was confirmed only last Friday.

The outbreak initially went undetected, because patients did not show typical Ebola symptoms, such as hemorrhaging, and because they had other illnesses, such as malaria, which complicated diagnosis, according to Ugandan officials.

Among the 14 dead are a medical clinic officer and her four-month-old baby, as well as 9 members from a single family. A dozen others suspected to be infected have been admitted to the local hospital, according to the Washington Post.

This is not the first time Ebola has struck Uganda: In 2007 an outbreak killed 42 people, and an epidemic in 2000 killed more than 200.

(Related: "Where Does Ebola Hide Between Epidemics?")

The virus is still so mysterious that no one knows how it originated, in which species it hides out between epidemics, or how to treat it. There's also a lack of understanding of how Ebola is transmitted, as Uganda's president demonstrated in a national address Monday.

"We discourage the shaking of hands, because that can cause contact through sweat which can cause problems ... and avoid promiscuity, because these sicknesses can also be transmitted through sex," Yoweri Museveni said in the address.

But the idea that Ebola can be spread by shaking hands—via sweat—is a myth, according to Joseph Fair, vice president of Metabiota, a San Francisco-based company that studies Ebola and other pathogens.

"Ebola is not currently known or thought to be transmitted by perspiration," Fair said. Ebola is transmitted by bodily fluids.

Overall, "being more aware of your surroundings and mindful of your contacts is always recommended if you live in the area of an outbreak."

Incredibly Lethal Virus

First reported in 1976 in the Democratic Republic of the Congo, Ebola is one of the most contagious known viruses. It's also incredibly lethal, killing up to 90 percent of its victims through widespread internal—and sometimes external—bleeding.

Initial symptoms can appear seemingly benign, and include vomiting, red eyes, stomach pains, and hiccups. (Take an infectious diseases quiz.)

Eventually the virus causes capillaries—tiny, branching blood vessels throughout the body—to leak, Fair explained.

"You essentially lose the junctures between your cell walls, so your capillaries are leaking. Once that happens, you lose blood pressure and you essentially die of shock ... It's an extremely uncomfortable death."

What's more, the few people who survive Ebola often find themselves treated as outcasts by neighbors who fear the survivors still carry the disease, even though the infection is not chronic like HIV.

"While HIV-prevention-and-education campaigns have been very effective, one unforeseen effect is that people think every infection is a chronic one that will be with you for life," Fair said.

(Also see "Ebola Killing Thousands of Gorillas, Study Says.")

Ebola Origins a Mystery

Discovering Ebola's host or hosts—called natural reservoirs—could also help scientists predict outbreaks and develop safety measures.

Some scientists have suggested that bats are Ebola's natural reservoirs, and there is some evidence to support this theory. For example, when researchers have injected bats with the Ebola virus in experiments, the bats have survived. (Related: "Fruit Bats Likely Hosts of Deadly Ebola Virus.")

But Ebola's protein structure also shares curious similarities with retroviruses carried by birds, leading some researchers to suspect the virus might have an avian origin.

One possible scenario is that Ebola evolved in birds in the distant past and was transmitted to bats, which now pass the virus on to humans and primates, said David Sanders, an Ebola researcher at Purdue University in Indiana.

It could even be that Ebola hides out in bats and birds.

"I am not opposing the idea that bats are a natural reservoir," Sanders said, "but I do not think birds have been or should be ruled out as a past host or even as a current host."

Ebola would not be the first virus to have a complicated past. The influenza virus, for example, originally infected only birds, but then jumped to humans, who might have then passed it on to pigs, Sanders said.

Now humans can catch the flu from both birds and pigs, as evidenced by the 2009 swine flu outbreak.

Ebola Vaccine on Horizon?

Despite being first reported nearly 40 years ago, there is still no treatment or cure for Ebola.

One reason is that Ebola is not a single virus but five different strains, or species. And as with influenza and HIV, each species of Ebola carries different surface proteins that can be targeted by our immune systems.

"Therefore, if you happen to mount an immune response against species 1 of Ebola, it would most likely not be protective against species 2, 3, 4, and 5," Sanders explained.

Sanders thinks the disease's limited scope is another reason no Ebola vaccine currently exists.

"How many Americans have died of Ebola? ... The answer is zero," he said. "We tend to focus on those diseases that affect us the most."

But the likelihood is greater that an Ebola vaccine might soon be developed, as the U.S. military is concerned Ebola could be used for bioterrorism.

"A lot of researchers have come into the field since 9/11," Sanders said. "It's clearly on the [U.S.] Department of Defense's radar."

(See "Ebola Cured in Monkeys—Hope for Humans?")

And it's not just the U.S. military that's interested in biodefense, Metabiota's Fair noted. Other federal agencies, including the U.S. Department of Agriculture, the National Institutes of Health, and the Department of Homeland Security have increased their biodefense budgets in the wake of 9/11. The European Union, Japan, and other countries have followed suit.

If military-funded research does lead to the successful development of an Ebola vaccine, it could ultimately benefit countries such as Uganda when the next natural outbreak strikes, the experts say.

"There's little doubt in my mind that advances in vaccines that are biodefense-oriented will have implications for defense against natural [Ebola] outbreaks," Sanders said.

"This is the way science works. You focus on one particular approach, but there are spin-offs for other things."

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