The epidemiology of malaria in the Papua New Guinea highlands: 1. Western Highlands Province

Despite a resurgence of malaria in many Papua New Guinea highlands and highlands fringe areas after the cessation of control activities in the early 1980s the malaria situation in these areas has received little attention. A series of cross-sectional surveys were therefore carried out to provide accurate and up-to-date information on the prevalence of malaria and the risk of epidemics and to propose adequate malaria control strategies. Studies in 24 villages in Western Highlands Province found the prevalence of malarial infections to be strongly correlated with altitude, ranging from 1.6% at altitudes of 1500-1800 m to over 30% in villages below 900 m. Malaria outbreaks were observed at the end of the rainy season. All four human malaria species were present with P. falciparum infections clearly dominating. The relative importance of P. vivax increased with altitude, while both P. malariae and P. ovale were rare. Many infections were of low density. While malaria is an important source of febrile illness in endemic areas below 1500 m altitude, only few observed or reported fevers are due to malarial infections in higher, nonendemic areas. Rates of enlarged spleens, mean haemoglobin levels and the prevalence of anaemia (Hb <7.5 g/dl) were strongly linked to the level of malaria found in each community and were associated with both altitude and concurrent malarial infection. Based on the survey results, areas of different malaria epidemiology are delineated and options for control in each area are discussed.

Complex patterns of malaria epidemiology in the highlands region of Papua New Guinea

A cross-sectional malaria survey of the Pabrabuk area in the Western Highlands Province found that all 4 human malaria species were present in a single village, with an overall parasite prevalence rate of 27%. Plasmodium falciparum was the most frequently detected infection (14%) followed by P. vivax (11%), P. malariae (5%) and P. ovale (3%). 10 of the 51 infections were mixed. Anopheles punctulatus was the most frequent vector species in the area, but both An. farauti no. 6 and An. karwari were also present in low numbers. This diversity in both parasite and vector populations indicates that complex malaria patterns are found in Papua New Guinea even at the moderate transmission levels found in low-lying inter-montane valleys.