Changing patterns of forest malaria among the mobile adult male population in Chumkiri District, Cambodia.

Forest malaria remains a major problem in many parts of Southeast Asia and South America. In Cambodia, where a significant reduction of malaria morbidity and mortality has been observed in the last 20 years, the forest malaria situation was studied in Chumkiri District by analysing the available passive case detection data and conducting malariometric (n=1018) and questionnaire surveys (n=374) in four forest-fringe villages. There has been a decreasing trend of malaria incidence from 2001. Plasmodium falciparum was highly predominant and P. vivax was rare. The nearby-forest villages showed significantly higher parasite rates than the far-from-forest villages (9.0% vs. 1.2%, p<0.01). Malaria was highly restricted to the male adults but was nearly non-existent in other accompanying family members, including small children and females. Low income and working in forests were strongly associated with the malaria risk. Our results suggest that transmission has greatly reduced in forest-fringe villages, but remains active in forests, which is primarily maintained between the forest vector Anopheles dirus and ethnic minority inhabitants. Specific interventions directed to these previously neglected in-forest inhabitants to protect themselves and male adult villagers during their forest activities are necessary to achieve an ultimate goal of malaria elimination from Cambodia.