There’s lots of ways of being a virus,” he tells us.

Some are relatively harmless and easily spread, like the cold virus. “Or you can take another strategy where you are not so nice to your host,” Mr. Zimmer says.

“That’s a risky strategy,” he points out. Every time a pathogen kills, it loses a place to live. So viruses sometimes also hang out in backup species – in Ebola’s case, probably bats.

And some evolve to move quickly from one host to another, like Ebola via body fluids.

“It performs this horrible trick of taking advantage of the way people care for their sick and honor their dead,” Mr. Zimmer says.

You are not likely to catch Ebola just by being in proximity with someone who has the virus; it is not airborne, like the flu or respiratory viruses such as SARS.

Instead, Ebola spreads through direct contact with bodily fluids. If an infected person’s blood or vomit gets in another person’s eyes, nose or mouth, the infection may be transmitted. In the current outbreak, most new cases are occurring among people who have been taking care of sick relatives or who have prepared an infected body for burial.

Health care workers are at high risk, especially if they have not been properly equipped with or trained to use and decontaminate protective gear correctly.

The virus can survive on surfaces, so any object contaminated with bodily fluids, like a latex glove or a hypodermic needle, may spread the disease.