Stay away from pools of standing water, areas where garbage is present, and typically any other place mosquito's are prevelant. Had a dengue scare in PR a year ago.... it is treatable but better to not get it.
Seriously, Doug and all the other JC'ers here: I am not a MD, however I had the opportunity to listen to my own Flight Surgeon followed by USAF Bio-Environmental Health specialists and DOS Regional Medical Officers (RMOs) at the US Embassies in Tanzania and Ghana before and during my trip to Africa last year.
I highly recommend that if you are going to be in a country where you might even be a little bit worried about what you can catch that you contact the US Embassy responsible for the country to which you are travelling to regarding your plans and specifically ask to speak with the RMO (Regional Medical Officer) with your concerns and precautions you should take. Better yet, have your doctor/AME contact the RMO for a consult. The RMOs for my countries worked in concert with my flight surgeon to ensure I had the correct malaria prophylaxsis and post-exposure treatment.
When I deployed, I worked with some indiviuals from several other government agencies who had access to the same health care system and the RMOs I had access to. At least four people from these OGAs contracted malaria during this trip and they were not on the phrophylaxsis I was on. My flight surgeon attributes it to the work he/she did with the RMO.
So the bottom line: When you are going abroad for travel or work, include the US Embassy team (especially the RMO) in your research. They exist to help all American Citizens have a successful journey.