Insecticidal Bed Nets and Filariasis Transmission in Papua New Guinea

Abstract

Global efforts to eliminate lymphatic filariasis are based on the annual mass ad- ministration of antifilarial drugs to reduce the microfilaria reservoir available to the mosquito vector. Insecticide-treated bed nets are being widely used in areas in which filariasis and malaria are coendemic. We studied five villages in which five annual mass administrations of antifilarial drugs, which were completed in 1998, reduced the transmission of Wuchereria ban- crofti, one of the nematodes that cause lymphatic filariasis. A total of 21,899 anoph- eles mosquitoes were collected for 26 months before and 11 to 36 months after bed nets treated with long-lasting insecticide were distributed in 2009. We evaluated the status of filarial infection and the presence of W. bancrofti DNA in anopheline mos- quitoes before and after the introduction of insecticide-treated bed nets. We then used a model of population dynamics to estimate the probabilities of transmission cessation. Village-specific rates of bites from anopheline mosquitoes ranged from 6.4 to 61.3 bites per person per day before the bed-net distribution and from 1.1 to 9.4 bites for 11 months after distribution (P<0.001). During the same period, the rate of detec- tion of W. bancrofti in anopheline mosquitoes decreased from 1.8% to 0.4% (P = 0.005), and the rate of detection of filarial DNA decreased from 19.4% to 14.9% (P = 0.13). The annual transmission potential was 5 to 325 infective larvae inoculated per person per year before the bed-net distribution and 0 after the distribution. Among all five villages with a prevalence of microfilariae of 2 to 38%, the probabil- ity of transmission cessation increased from less than 1.0% before the bed-net dis- tribution to a range of 4.9 to 95% in the 11 months after distribution. Vector control with insecticide-treated bed nets is a valuable tool for W. bancrofti elimination in areas in which anopheline mosquitoes transmit the parasite.