The thick forests along the northern borders of Thailand are excellent breeding grounds for anopheles mosquitoes, which infect people with a disease-causing parasite. Rugged terrain and heavy rainfall limit the use of sprays to control the insect. Coupled with poor living environments and activities like mining which create new habitats for mosquitoes, these conditions have helped revive a scourge that Thailand all but eliminated 50 years ago - malaria. In 1997, for example, there were about 100,000 documented cases in the country. But the parasites aren't.
Some doctors even describe the border provinces as the global epicenter of malaria resistance.
Indeed, the first ever signs of immunity to the historic remedy, quinine, surfaced in the country in the late 1950s. Thailand, too, was where parasites began to show resistance to chloroquine, the cheapest and safest malaria drug. How super-virulent strains of malaria arise is not fully understood, but officials acknowledge that indiscriminate use of medicines is a contributing factor. The disease is caused by four types of plasmodium, a single-cell parasite transmitted via mosquitoes. These then travel to the liver, where they multiply and turn into a different kind of spore call merozoite.