Revisiting the basic reproductive number for malaria and its implications for malaria control

The prospects for the success of malaria control depend, in part, on the basic reproductive number for malaria, R₀. Here, we estimate R ₀ in a novel way for 121 African populations, and thereby increase the number of R₀ estimates for malaria by an order of magnitude. The estimates range from around one to more than 3,000. We also consider malaria transmission and control in finite human populations, of size H. We show that classic formulas approximate the expected number of mosquitoes that could trace infection back to one mosquito after one parasite generation, Z₀(H), but they overestimate the expected number of infected humans per infected human, R₀(H). Heterogeneous biting increases R₀ and, as we show, Z₀(H), but we also show that it sometimes reduces R₀(H); those who are bitten most both infect many vectors and absorb infectious bites. The large range of R₀ estimates strongly supports the long-held notion that malaria control presents variable challenges across its transmission spectrum. In populations where R₀ is highest, malaria control will require multiple, integrated methods that target those who are bitten most. Therefore, strategic planning for malaria control should consider R₀, the spatial scale of transmission, human population density, and heterogeneous biting.