Heightened transmission of stable malaria in an isolated population in the highlands of Irian Jaya, Indonesia

Abstract

Malaria at an elevation of 1,500 meters is uncommon and is usually unstable when it occurs. To confirm reports of a recent increase in transmission of stable malaria in the Oksibil Valley, which is at an elevation of 1,250-1,500 meters in the Jayawijaya Mountains of Irian Jaya, Indonesia, five malariometric surveys were conducted in four villages between May 1990 and July 1991. A total of 3,380 blood smears, representative of 1,949 persons, was examined. Prevalence rates over the survey period were consistent in each of the four villages, averaging 10% for infants, 50% for children 1-4 years of age, 35% for those 5-9 years old, 28% for those 10-14 years old, and 16% for adults (greater than 15 years old). The spleen rate for the those less than five years old was 96%, with an average enlarged spleen score of 2.32. Plasmodium falciparum accounted for 55% of the infections in the valley, but P. vivax was the predominant species in those less than 10 years old. In the village of Kutdol at an elevation of 1,500 meters, P. malariae was identified in 43% of the positive smears. Four cases were diagnosed as P. ovale. Infection with P. falciparum without obvious clinical symptoms was common in both adults and children. Entomologic and epidemiologic data suggested that the recent upsurge in transmission coincided with the replacement of traditional village huts with the more modern social housing. This replacement required the extensive construction of drainage ditches, which inadvertently also served as additional vector breeding sites. We suspect that this manipulation of the environment, in an effort to improve the quality of life, created conditions conductive for heightened transmission of stable malaria.

PIP: Malaria at an elevation of 1500 meters is uncommon and is usually unstable when it occurs. To confirm reports of a recent increase in the transmission of stable malaria in the Oksibil Valley, at an elevation of 1250-1500 meters in the Jayawijaya Mountains of Irian Jaya, Indonesia, 5 malariometric surveys were conducted in 4 villages between May 1990 and July 1991. A total of 3380 blood smears from 1949 people was examined. Prevalence rates over the survey period were consistent in each of the 4 villages,with averages of 10% for infants, 50% for children 1-4 years old, 35% for those 5-9 years old, 28% for those 10-14 years old, and 16% for adults (over 15 years of age). The spleen rate for those less than 5 years old was 96%, with an average enlarged spleen score of 2.32. Plasmodium falciparum accounted for 55% of the infections in the valley, but P. vivax was the predominant species in those less than 10 years old. In the village of Kutdol, at an elevation of 1500 meters, P. Malariae was identified in 43% of the positive smears. 4 cases were diagnosed as P. ovale. Infection with P. falciparum without obvious clinical symptoms was common in both adults and children. Entomologic and epidemiologic data suggested that the recent upsurge in transmission coincided with the replacement of traditional village huts with more modern social housing. This replacement required the extensive construction of drainage ditches, which inadvertently also served as additional vector breeding sites. The authors suspect that this manipulation of the environment, while attempting to improve the quality of life, created conditions which were conducive for the increased transmission of stable malaria.