you have to keep your options open. in terms of something new. if anything, we have learned to expect the unexpected basically. there are new diseases with new twists in terms of exposure, et cetera. i am more worried about the things we don't know about. >> knowing about these viruses is the first step. before some of these pathogens reach the lab, they come here. >> there are only a few people that have space here. david mckenzie has been taking us on this journey with a team of south african virus hunters. the last stop is here, a level 4 bio lab in south africa. the highest bio security level and the only lab of its kind on the after can continent.