How contagious is Ebola? And how worried should you be about the current outbreak?

Ebola cases have increased sharply each day since a public health emergency was declared. The latest figures report more than 600 suspected cases and 139 suspected-Ebola deaths. Most cases are in a remote province in northeastern Democratic Republic of Congo, an area affected by decades of conflict, with additional cases reported in Uganda’s capital. The World Health Organization identified the Ebola strain as rare and suggested the outbreak may have started months before it was detected. Ebola outbreaks have almost always begun in east or west Africa, and the Democratic Republic of Congo has detected the most outbreaks. The source of human infection remains uncertain, with suspicions focused on exposure to bats through bat meat or bat guano, including scenarios involving miners and caves. Spillover from an infected animal to a person can then lead to person-to-person spread.

"The number of Ebola cases has been growing and growing by a lot each day since the World Health Organization declared a public health emergency on Saturday. The latest toll? More than 600 suspected cases and 139 suspected-Ebola deaths. The vast majority of the cases are in a province in northeastern Democratic Republic of Congo a remote place struggling after decades of bloody conflict. There are also two cases in Uganda's capital."

"The World Health Organization has identified the strain of Ebola as a rare one and says the outbreak could have started months before it was detected. "This is an example of a perfect storm," says Dr. Abraar Karan, an infectious disease physician and faculty at Stanford University. Since it's been more than a decade since the large West Africa Ebola outbreak, here is what you need to know about this virus and what's on the minds of infectious disease experts as they look at the current outbreak."

"Geographically, this is easy to answer: Ebola outbreaks have almost always started in either east and west Africa. By far, the Democratic Republic of the Congo has detected the most outbreaks. This is its 17th since 1976. Exactly how humans pick up the virus remains a question mark. "We don't know for sure where it comes from but we have suspicions," says Karan, whose team has been studying Ebola and related viruses in Kenya for several years."

"The leading guess, he says, is that people get Ebola from eating bat meat or being exposed to bat guano or excrement. This could happen when miners go into caves. "A number of animals have also tested positive for antibodies, so certain types of deer called duiker that eat meat have been implicated. Non-human primates have shown antibodies," he says. What tends to happen is that one person gets it from an animal which is called a spillover and then that individual spreads it to other people."

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