The epidemiology of malaria in the Papua New Guinea highlands: 6. Simbai and Bundi, Madang Province.

Although predominantly a lowland province, Madang also includes highland areas such as Simbai and Bundi along the northern highland fringe. While the malaria situation in the coastal lowlands has been studied in great detail, the current malaria situation in the highland fringe communities has not been studied in depth since the 1960s. A series of recent malariological surveys found that the malaria situation has changed little over the last 40 years in both Simbai and Bundi. In the Simbai area there is little malaria transmission in villages above 1400 m, with a prevalence rate (PR) of 2.5-4.2%. Below 1400 m, however, there is moderate to high transmission (PR 8.6-24.7%) with surprisingly little difference in prevalence rates between survey villages, despite large differences in altitude. Prevalence rates of malaria infection were low in all Bundi villages (2.5-8.5%) with most infections occurring in adolescents and adults, which indicates limited acquisition of effective immunity to malaria and the possibility that many infections are acquired when travelling to the highly malarious lowlands area. Based on spleen rates the lower Simbai area would be regarded as mesoendemic, and the upper Simbai and Bundi areas as hypoendemic. Only in the lower Simbai area is malaria a major cause of febrile illness. However, in all areas village mean haemoglobin (Hb) levels were highly correlated with the prevalence of malaria infections, while concurrent parasitaemia reduced individual Hb levels by 1.3 g/dl (CI95 [1.0-1.5], p < 0.001) and significantly increased the risk for moderate-to-severe anaemia (Hb < 8 g/dl) (adjusted odds ratio 5.6, CI95 [3.6-8.6], p < 0.001). Based on the survey results, areas of different malaria epidemiology are delineated and options for control in each area are discussed.