Some examples would be Hepatitis A, Yellow Fever, Typhoid Fever, Rabies - there's numerous diseases that people should be aware of and possibly vaccinated for if they are planning to travel. If there is no immunity and a traveler is exposed to some of these viruses, then you have a possibly life threatening illness.
Dr. John D. Cahill, M.D. is a physician and medical educator who founded the Center for Global Collaboration & Health Initiatives. While studying abroad in medical school and after his postgraduate medical training at Brown University, Dr. Cahill spent time in Southeast Asia & Africa.