Abstract
Mosquito feeding assays are important in evaluations of malaria transmission-reducing interventions. The proportion of mosquitoes with midgut oocysts is commonly used as an outcome measure, but in natural low intensity infections the effect of oocyst non-rupture on mosquito infectivity is unclear. By identifying ruptured as well as intact oocysts, we show that in low intensity P. falciparum infections i) 66.7–96.7% of infected mosquitoes experienced oocyst rupture between 11–21 days post-infection, ii) oocyst rupture led invariably to sporozoite release, iii) oocyst rupture led to salivary gland infections in 97.8% of mosquitoes, and iv) 1250 (IQR 313-2400) salivary gland sporozoites were found per ruptured oocyst. These data show that infectivity can be predicted with reasonable certainty from oocyst prevalence in low intensity infections. High throughput methods for detecting infection in whole mosquitoes showed that 18s PCR but not circumsporozoite ELISA gave a reliable approximation of mosquito infection rates on day 7 post-infection.
Highlights
Mosquito feeding assays are important in evaluations of malaria transmission-reducing interventions
The presence or intensity of oocysts observed on mosquito midguts, which for P. falciparum can be reliably detected by microscopy as early as day 6 PI6, is commonly used as an operationally attractive outcome measure that may be amendable for high throughput processing by immunological or molecular methods
Gametocyte culture material was diluted with uninfected blood to achieve oocyst intensities that are in line with the 1–5 oocysts typically observed in natural P. falciparum infections
Summary
Mosquito feeding assays are important in evaluations of malaria transmission-reducing interventions. The presence or intensity of oocysts observed on mosquito midguts, which for P. falciparum can be reliably detected by microscopy as early as day 6 PI6, is commonly used as an operationally attractive outcome measure that may be amendable for high throughput processing by immunological or molecular methods. This requires that the detection of any number of oocysts should reasonably predict their likelihood of causing mosquito infectivity[2]. The impact of oocyst arrest in low intensity infections might decrease the reliability of oocyst prevalence as an indicator of infectivity because it could lead to the total failure of sporozoite release
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