Malaria is a serious vector borne disease that is endemic to the areas you mention. It is one of the top 3 causes of deaths from infectious diseases worldwide and a serious risk to travelers.
You should consult the CDC and US State dept websites to check up on specific information and prophylatic drug regamens for each specific country you plan to visit or stay in. A different drug may be required in a different area. You will need to be very specific about this.
And yes, buy the drugs in the US. Have a prescription with you as you travel.
Hope this helps