Spatial variation of Anopheles-transmitted Wuchereria bancrofti and Plasmodium falciparum infection densities in Papua New Guinea

Abstract

The spatial variation of Wuchereria bancrofti and Plasmodium falciparum infection densities was measured in a rural area of Papua New Guinea where they share anopheline vectors. The spatial correlation of W. bancrofti was found to reduce by half over an estimated distance of 1.7 km, much smaller than the 50 km grid used by the World Health Organization rapid mapping method. For P. falciparum, negligible spatial correlation was found. After mass treatment with anti-filarial drugs, there was negligible correlation between the changes in the densities of the two parasites.

Figure 1

Spatial variation of a) W. bancrofti and b) P. falciparum in parts of Urim and Urat census districts, East Sepik Province. The scale is in kilometres with an arbitrary origin near the centre of the study area (142.7°E, 3.6°S). Each hexagon represents one hamlet, with the shading showing the quartile of the standardized parasite density ratio. For W. bancrofti, the 0, 25, 50, 75 and 100th percentiles are 0.27, 0.56, 1.02, 1.71 and 4.3 respectively. For P. falciparum they are 0.43, 0.94, 1.27, 1.80 and 11.64. The curve plotted against the vertical axis shows the rate at which correlation in mean parasite density decays with distance. The solid lines in the body of the map show unpaved roads, and the dashed line indicates the division of villages between the two census districts.