Daniel heard someone say the word Ebola at school. The room went quiet.

He wants to know why.

The answer turns out to be more complicated than most people expect. Because lots of diseases kill people. Measles kills hundreds of thousands every year. Tuberculosis kills over a million. Yet those names don't make a room go quiet the way Ebola does. So the fear was never just about the numbers.

Here is what Ebola actually is. It is a virus first identified in 1976 near the Ebola River in what is now the Democratic Republic of Congo. In some early outbreaks, more than half the people who caught it did not survive. That case fatality rate -- among the highest of any known virus -- was what immediately frightened doctors.

And then there is the part most people don't know.

Ebola does not spread through the air. It spreads thr ...