With global travel, diseases uncommon in the developed world are increasingly being seen. I am fascinated by infectious diseases, one of my favorite movies being "Outbreak," so ID news tends to catch my attention. One that recently made headlines was Marburg hemorrhagic fever, contracted by a tourist in Uganda. He likely caught it when he visited a python cave and encountered fruit bats. The virus, a member of the filovirus family which includes Ebola, was only discovered in 1967 - ironically, it was transmitted by African green monkeys imported for research and to prepare polio vaccines. Check the CDC page for more details on the background and symptoms.
It's pretty scary to think how unprepared the medical field is for rare, contagious diseases from the third world. So many viral infections start out with flu-like symptoms that the person would not be treated or quarantined, and it would be easy to transmit the disease to other people. With an incubation period of 5-10 days, plenty of people could become infected.
With global warming, in addition to global travel, I'm confident we will begin seeing more tropical diseases, particularly those carried by insect vectors. The range of mosquitoes capable of transmitting Dengue has spread across the southern United States, the Hemipteran responsible for Chaga's disease may be able to spread north from Mexico, and West Nile Virus is already found across the country. Cases of Dengue fever have occurred endemically in Texas. It will be interesting to see how the geography of tropical diseases continues to evolve.