I don’t think there is any worst disease. Like Ebola, or any other diseases, we were able to make vaccine. So there isn’t any fatality-one hundred percentage disease (at least I think so) yet. But the virus will get stronger and stronger (develop or have evolution) as we find out the vaccine. It’s so unfair that diseases develop fast and also stronger but we need time to figure it out. It sounds quit strange, but if the environment totally changes, or our science technology develops, we might encounter totally new things, including new diseases. Those may be badly-disease that we can’t follow with now-days’ technology. So we don’t have the worst disease ‘yet’.