in sars was a bat. and we think based on our analysis and the sequence of this virus that it also originated in a bat. >> reporter: where? >> well, probably somewhere in the middle east. >> reporter: health officials don't know much about how the virus spreads, but at this point, travel warnings have not been issued. >> i don't think we should be concerned in terms of travel to the middle east or to anywhere in the world right now, but to just be aware of it. most of the cases and illnesses have been associated with the elderly and those with pre-existing or severe underlying medical conditions. >> reporter: the world health organization is so concerned about this virus because there's no known treatment and no way to make a vaccine, not just yet. doctors are currently working on that. in the cases that have been found in eight countries, all have been linked to the middle east. mary snow, cnn, new york. >> those stories always terrify me, those, you know, unexplained, we don't know what it is and how it's killing people, but it is. there are only eight cases, but