AGE-SPECIFIC PREVALENCE OF PLASMODIUM-FALCIPARUM AMONG 6 POPULATIONS WITH LIMITED HISTORIES OF EXPOSURE TO ENDEMIC MALARIA

The age-specific prevalence of Plasmodium falciparum parasitemia among residents of six villages in northeastern Irian Jaya, Indonesia, has been measured for a period of five years. All study subjects were tran smigrants from Java living in Irian Jaya for three weeks to 72 months, depending upon the village and point of measurement. Fifteen separate estimates of prevalence were obtained from 4,554 Giemsa-stained thick blood films from 91 to 701 people (mean sample size = 304) among the six villages. The prevalence of parasitemia among people who had lived in Irian Jaya for less than one year did not decrease as a function o f age, except in one village at eight months. In contrast, after 16 mo nths to two years or more of residence, the prevalence of parasitemia decreased markedly with increasing age beyond 6-10 or 11-15 years. Soc ial, behavioral, or entomologic characteristics of these populations d id not explain the decreasing prevalence of parasitemia with age. An a ge-dependent naturally acquired protective immunity appeared to develo p in all of these villages after 1-2 years of exposure to hyperendemic malaria.