Because it is a virus, it is very different than pertussis which is a bacteria. (If your dog gets kennel cough, it is usually a form of bacterial purtussis.) Bacteria can be carried by many hosts and live in the natural world itself. The smallpox virus needed a human host. Unless Russia or the US CDC goes rogue and tries to use the variola virus as a bioweapon, you are probably pretty safe from it. It's really not something to loose sleep worrying about. Other germs? yes. But not this one.