Malaria, filariasis, dengue and many other human and animal diseases are transmitted by mosquitoes. During the Global Malaria Eradication Campaign, George Macdonald defined R0 for malaria and a described a basis for estimating it. (The name and notation originated in demography with Lotka). Vectorial capacity describes the vector-specific aspects of R0, including vector ecology, demography, bionomics, and behavior. A common practice is to model vector transmission as "quasi-direct," either implicitly or explicitly using approximation from a minimal mosquito model in which vectorial capacity is analogous to the contact parameter from directly transmitted disease models. I will discuss three problems with this approach.
First, vectorial capacity is inversely proportional to human population density, unlike density-dependent or frequency dependent transmission. Consistent with the corollary that high human population density dilutes transmission, malaria prevalence tends to be lower in urban areas. Second, confidence in quantitative estimates of R0 have been undermined by a discrepancy between entomological and epidemiological measures of malaria exposure. I'll show estimates of the key parameters, and present an analysis suggesting that heterogeneous biting explains the discrepancy, a fact that raises more questions than it answers. Third, disease control programs both create and ignore heterogeneity, and this can seriously undermine their success. A research agenda for the next ten years is to clarify which details matter for the dynamics and control of mosquito borne diseases, which details can be ignored, and which ones are like the nuisance mosquito buzzing in your ear.
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