What Causes Infectious Diseases to Strike? Since the seventies, many knew diseases have been dicovered in many different parts of the world. The new diseases are all of an infectious nature, meaning that they are viral infections, not bacterial infections. The main difference between viral diseases such as Marburg and Ebola and other viral diseases like Inlfuenza is how unpredictaable they are. The newest infectious diseases are not seasonal. They occur in swift deadly waves called outbreaks. While hundreds of scientists have documented the effect of outbreaks and the different circumstances under which they occur, no conclusive evidence has been gathered