Malaria is a big problem in Myanmar. Not in Yangon or Mandalay, because the malaria mosquito doesn't exist in urban environments. but the majority of the Myanmar population live in rural areas.
The World Health organisation says half a million in Myanmar have it. Medecins Sans Frontieres, who run clinics in Myanmar, say it's more like TEN MILLION!
WHO in Feb 2010 reported that tolerance to Artemisinin, the most effective anti-malarial drug, is showing up in Myanmar.
Best precaution: don't get bitten by mosquitoes in the first place. That has the added benefit of protecting you from Dengue Fever (which is on the rise worldwide). The mosquito that gives you Dengue Fever DOES exist in cities. This year there've been 900 cases in Yangon district and 6 people have died from it.
Bite prevention: wear long, loose-fitting, white sleeves and long trousers.Put DEET repellent on exposed skin. Use repellent coils in rooms (day and night) and sleep under bed nets treated with insect repellent. about 10 years ago