Hi, there's definitely anti malarial drugs readily available if you are in the Malaria infested or malaria prone regions.
For someone moving to a Malaria prone area, i definitely would recommend taking the anti malarial meds dosage at least a few days or a week prior to the visit. If the meds are not easily accessible then i'd recommend they start the dosage soon as they arrive.
i am not sure if anti Dengue meds are available, i think there in No.
Most important ways of prevention from both diseases would be to employ all measures to avoid mosquito bites. Personal protection and environmental protection are key. These are way more important in the long run than taking the anti malarial meds.
To the question in your title, my Magic 8-Ball says:
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