US Malaria Casualties and Chemoprophylaxis during the Vietnam War.

Malaria caused mass casualties among US military personnel during the Vietnam War, resulting in as many hospitalizations as combat wounds in 1965. Its military impact was magnified because nearly all the disease-related casualties came from front-line units, particularly the infantry, with rates exceeding 10 per 1,000 man-days of exposure. The imperfect chemoprophylaxis using chloroquine-primaquine tablets developed during the Korean War proved inadequate. Adding daily dapsone was more effective but resulted in rare cases of agranulocytosis and at least eight deaths. After Vietnam, malaria in US military members, especially relapsing malaria due to Plasmodium vivax, caused thousands of infections in the United States, although indigenous transmission was rarely observed. Although severe malaria resulted in 78 known deaths in the US Army (and 46 in the US Marines), the real military issue was lost days due to illness, averaging more than 1 month per malaria case and at least 200,000 lost man-days per year. Malaria's potential to produce mass casualties in soldiers remains, especially during deployments to New Guinea or sub-Saharan Africa.