The potential impact of integrated malaria transmission control on entomologic inoculation rate in highly endemic areas

Abstract

We have used a relatively simple but accurate model for predicting the impact of integrated transmission control on the malaria entomologic inoculation rate (EIR) at four endemic sites from across sub-Saharan Africa and the southwest Pacific. The simulated campaign incorporated modestly effective vaccine coverage, bed net use, and larval control. The results indicate that such campaigns would reduce EIRs at all four sites by 30- to 50-fold. Even without the vaccine, 15- to 25-fold reductions of EIR were predicted, implying that integrated control with a few modestly effective tools can meaningfully reduce malaria transmission in a range of endemic settings. The model accurately predicts the effects of bed nets and indoor spraying and demonstrates that they are the most effective tools available for reducing EIR. However, the impact of domestic adult vector control is amplified by measures for reducing the rate of emergence of vectors or the level of infectiousness of the human reservoir. We conclude that available tools, including currently neglected methods for larval control, can reduce malaria transmission intensity enough to alleviate mortality. Integrated control programs should be implemented to the fullest extent possible, even in areas of intense transmission, using simple models as decision-making tools. However, we also conclude that to eliminate malaria in many areas of intense transmission is beyond the scope of methods which developing nations can currently afford. New, cost-effective, practical tools are needed if malaria is ever to be eliminated from highly endemic areas.

Figure 1

A: Simulated between-site variations in the size of the infectiousness of the human reservoir κ. B: The lifetime malaria transmission capacity of individual vectors (L); C: Mosquito emergence rate relative to the size of the human population E/N_h; D: The entomologic inoculation rate (EIR); and E: The human biting rate (H_Bt). Baseline conditions are represented by empty bars and those of an integrated transmission control program by solid bars. For further details of definitions and units see Killeen and others.

Figure 2

Predicted between-site variations in vector survival per feeding cycle (P_f), blood-feeding preferences (Q), number of human bites per lifetime (b_h), number of infectious human bites per lifetime (β), sporozoite prevalence (S), and infectious bites per lifetime per bite on an infective human host (L) under baseline conditions (empty bars) and those of an integrated transmission control program (solid bars). See Killeen and others for further details of definitions and units.