We haven't had any problems in those areas, but take your (AUTAN) Insect and Mozzie spray, with you because things from the chemists over there can be mega expensive, espcialy headach type drugs etc.
For full protection and to set your mind at ease you can go to your doctors and make an appointment with the practice nurse who will give you a jab to cover the lot, I had one years ago and I think it was free.
Enjoy your trip.
Have done the places you are going. and never took any tablets. you will only be in one place for a day and the only thing i would take is insect repellent if going into a rain forest or jungle.
We are doing similar cruise in this area in a couple of weeks and our GP's advice is no problems as long as you don't venture into the swamps and jungle! The beaches and touristy places are mozzy free ....usually .Just use repellent wipes etc.
We have been to the same places as well and only took an insect repellent we were fine.
Take a good insect repellant - should contain 'deet' and you will be fine.