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Malaria was eradicated and the Republic of Korea (ROK) declared "malaria free" in 1979. However, in 1993, a temperate strain of vivax malaria, expressing both latent and nonlatent disease populations, re-emerged near the demilitarized zone (DMZ), rapidly spread to civilian sectors near the DMZ, and increased exponentially in ROK military, veteran, and civilian populations through 1998. Malaria among all ROK populations decreased 5-fold from a high of 4142 cases in 2000 to a low of 826 cases in 2004, before increasing again to 2180 cases by 2007. Each malaria case in the ROK is reported in the metropolitan area/province where the diagnosis is made, which may be at some distance from the area where infection occurred. Therefore, it is difficult to ascertain transmission sites since approximately 60% of vivax malaria in Korea is latent with symptoms occurring >1 month to 24 months after infection. A review of case diagnosis for civilian, veteran, and military populations shows that nearly all malaria south of Gyeonggi and Gangwon Provinces is the result of veterans exposed in malaria high-risk areas along the DMZ and returning to their hometowns where they later develop malaria. Thus, malaria currently remains localized near the DMZ with limited transmission in provinces south of Seoul and has not spread throughout Korea as previously hypothesized. This report describes the reemergence of vivax malaria cases in civilian and military ROK populations and U.S. military personnel and assesses variables related to its transmission and geographic distribution.

Malaria is a significant health threat to U.S. combat forces that are deployed to malaria-endemic regions. From 1979, when the Republic of Korea (ROK) was declared malaria free, malaria did not present a health threat to U.S. forces deployed to Korea until the early 1990s. In 1993, a temperate strain of vivax malaria expressing both latent (long prepatent incubation periods of usually 6-18 months after infection) and nonlatent (short prepatent incubation periods < 30 days after infection) disease reemerged near the demilitarized zone (DMZ) and once again presented a primary health threat to U.S. military populations in the ROK. Following its reemergence, malaria rates increased dramatically through 1998 and accounted for > 44% of all malaria cases among U.S. Army soldiers from 1997 to 2002. More than 60% of all Korean-acquired malaria among U.S. soldiers was identified as latent malaria. Nearly 80% of all latent malaria attributed to exposure in Korea was diagnosed in the U.S. or other countries where soldiers were deployed. These data illustrate the requirement for a comprehensive malaria education program, especially for those soldiers residing or training in malaria high-risk areas, to inform soldiers and providers of the risk of developing malaria after leaving Korea.