Abstract
The efficiency of malaria transmission between human and mosquito has been shown to be influenced by many factors in the laboratory, although their impact in the field and how this changes with disease endemicity are unknown. Here we estimate how human–mosquito transmission changed as malaria was controlled in Dielmo, Senegal. Mathematical models were fit to data collected between 1990 and the start of vector control in 2008. Results show that asexual parasite slide prevalence in humans has reduced from 70 to 20%, but that the proportion of infectious mosquitoes has remained roughly constant. Evidence suggests that this is due to an increase in transmission efficiency caused by a rise in gametocyte densities, although the uneven distribution of mosquito bites between hosts could also contribute. The resilience of mosquito infection to changes in endemicity will have important implications for planning disease control, and the development and deployment of transmission-reducing interventions.
Highlights
The efficiency of malaria transmission between human and mosquito has been shown to be influenced by many factors in the laboratory, their impact in the field and how this changes with disease endemicity are unknown
There are many possible reasons for this trend[1,2,3,4,5,6,7,8,9,10], the data suggest that it may be in part caused by an increase in gametocyte density in gametocyte-positive patients
Over the course of the study, the increase in gametocyte density is comparable to the increase in transmission efficiency predicted by the model
Summary
The efficiency of malaria transmission between human and mosquito has been shown to be influenced by many factors in the laboratory, their impact in the field and how this changes with disease endemicity are unknown. These include hosts anaemia[1], immunity[2] and drug treatment[3]; parasite (gametocyte) density[4], maturity[5] and clone diversity[6]; and mosquito size[7], microbial gut flora[8], environment[9] and immune response[10] among others These explanatory variables are rarely collectively measured, making it difficult to predict how transmission efficiency changes between locations and following the introduction of control interventions. The Dielmo Project in Senegal started in 1990 and has regularly estimated human and mosquito prevalence in the same village for the last 23 years[15,16] These data provide a unique data set to test whether human–mosquito transmission efficiency has changed as malaria has been controlled. Results indicate that as malaria has been successfully controlled transmission efficiency has increased, possibly through an increase in gametocyte density in infected individuals
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