Sea salt
In Southeast Asia, the medicated salt project at Pailin, on the Kampuchea-Thai border, demonstrated how drug resistance can develop when a large population of "P. falciparum" undergoing high transmission rates is exposed to intense drug pressure. The project was launched in 1960 and covered a population of approximately 20,000. Sea salt was mixed with pyrimethamine at a concentration of 0.05%. Between 1960 and 1961, 77 tons of medicated salt were distributed in the area. After widespread pyrimethamine resistance was reported, pyrimethamine was replaced by chloroquine. From 1961 to 1962, 75 tons of chloroquine were distributed. In two indicator districts, the parasite rates decreased from 40% to 7% and from 27% to 14%. Chloroquine resistant "P.falciparum" isolates were first detected in Pailin in 1962 which appeared to be widespread by 1966. However no survey was undertaken to document the prevalence in the area. The factors leading to the emergence and spread of drug resistance appear to have been the continuous introduction of non-immune migrants, attracted by the promise of quick wealth from mining of precious stones, and prolonged drug pressure resulting from individual drug consumption and mass drug administration. Unrelated to MDAs the emergence of artemisinin resistant "P.falciparum" strains was reported in Pailin in 2008, this may have been related to overuse of artemisinin derivatives including counterfeit drugs but was not related to programmatic MDAs.