Predicting mosquito infection from Plasmodium falciparum gametocyte density and estimating the reservoir of infection

Thomas S Churcher,María-Gloria Basáñez,Martin Walker,Chris Drakeley,Petra Schneider,André Lin Ouédraogo,Teun Bousema

doi:10.7554/elife.00626

Abstract

Transmission reduction is a key component of global efforts to control and eliminate malaria; yet, it is unclear how the density of transmission stages (gametocytes) influences infection (proportion of mosquitoes infected). Human to mosquito transmission was assessed using 171 direct mosquito feeding assays conducted in Burkina Faso and Kenya. Plasmodium falciparum infects Anopheles gambiae efficiently at low densities (4% mosquitoes at 1/µl blood), although substantially more (>200/µl) are required to increase infection further. In a site in Burkina Faso, children harbour more gametocytes than adults though the non-linear relationship between gametocyte density and mosquito infection means that (per person) they only contribute slightly more to transmission. This method can be used to determine the reservoir of infection in different endemic settings. Interventions reducing gametocyte density need to be highly effective in order to halt human-mosquito transmission, although their use can be optimised by targeting those contributing the most to transmission. DOI:http://dx.doi.org/10.7554/eLife.00626.001.

Highlights

The malaria parasite is transmitted among humans by anopheline mosquitoes
In the human malaria parasite Plasmodium falciparum, mosquito infection is thought to increase with the number of gametocytes ingested by the mosquito (Jeffery and Eyles, 1955; Graves et al, 1988; Bousema and Drakeley, 2011)
The complex shape of the relationship between gametocyte density and mosquito infection elucidated here will influence our understanding of the population dynamics of falciparum malaria and will determine the success of transmission-reducing interventions

Summary

Introduction

The malaria parasite is transmitted among humans by anopheline mosquitoes. In the human malaria parasite Plasmodium falciparum, mosquito infection is thought to increase with the number of gametocytes ingested by the mosquito (Jeffery and Eyles, 1955; Graves et al, 1988; Bousema and Drakeley, 2011). Difficulties arise because estimates of gametocyte density have relied on microscopy, which may miss up to 80% of parasites (Dowling and Shute, 1966). More sensitive molecular methods such as Pfs25mRNA quantitative nucleic acid sequence–based amplification (QT-NASBA) have been developed (Schneider et al, 2004). Unlike conventional microscopy, this technique enables gametocyte densities to be quantified over the entire epidemiologically relevant range

Methods

Results

Conclusion